Ab initio molecular orbital theory is used to determine if the molecular ion HOC+ is linear (as are the isoelectronic species HCN, HNC, HCO+, etc.), or if it is quasilinear. Near the Hartree-Fock limit the molecule is either linear, or very close to linear. Electron correlation favors the linear geometry, leading to the unequivocal prediction of a linear molecule. Detailed comparisons between HOC+ and isoelectronic HNC show an apparent lack of convergence in the bending potential for the former which is remedied by the addition of f functions to the basis set. The HOC+ potential energy surface is computed in the bending and bend-stretch coordinates and fit to an analytical function. Use of this function to compute the rotation-vibration energies results in improved agreement with experiment relative to previous potentials by nearly two orders of magnitude, as documented in the accompanying paper.

Frequencies of pure rotational transitions of isotopic species of water, H217O, and H218O were measured in the 1-5 THz region with a high-precision far-infrared spectrometer using a tunable radiation source. Measured frequencies of more than 100 spectral lines for each species provide an excellent frequency standard for the far-infrared region. Molecular parameters based on a Watson-type Hamiltonian have been obtained to reproduce the observed frequencies. Copyright 1999 Academic Press.

The pi --> pi* and n --> 5s absorption spectra of selenoformaldehyde, CH2Se and CD2Se, are reported. Both spectra are diffuse. The pi --> pi* transition extends from 243 to 210 nm with an extensive Franck-Condon profile and intensity maximum estimated at 230 nm. The Rydberg n --> 5s transition is superimposed on the pi --> pi* system. While still diffuse, the system is less extensive and shows an intensity maximum at 235 nm. The corresponding Rydberg transition of the deuterated species is blue shifted by 140 cm-1. Copyright 1999 Academic Press.

The (1 0(0) 5)1,2 --> (1 0(0) 4)1,2 and (1 0(0) 6)1,2 --> (1 0(0) 5)1,2 emission bands of 12C16O2 have been recorded near 4.5 µm by Fourier transform spectroscopy of a CO2 + N2 mixture excited by dc discharge. The spectroscopic parameters of the (1 0(0) v3)1,2 vibrational states with v3 = 0-6 have been obtained from a global rotational analysis of the six (1 0(0) v3)1,2 --> (1 0(0) (v3-1))1,2 emission bands (v3 = 1-6). The (1 0(0) 5)1,2 vibrational states of both 12C16O2 and 13C16O2 have been observed by direct absorption from the vibrational ground state by Intracavity Laser Absorption Spectroscopy near 12 700 and 12 400 cm-1, respectively. The rovibrational energy levels obtained by the two experimental techniques are discussed and compared with those calculated in the framework of the effective operator approach. Copyright 1999 Academic Press.

We have recorded the infrared absorption spectrum of pyrrole at 0.005 cm-1 spectral resolution using a Fourier transform interferometer. The rotational analysis of the symmetric out-of-plane C-H bend 22(1)0 fundamental band at 722.132993(5) cm-1 was performed, allowing 6760 lines to be assigned. These lines were fitted simultaneously to literature data on nu1 [A. Mellouki, R. Georges, M. Herman, D. L. Snavely, and S. Leytner, Chem. Phys. 220, 311-322 (1997)] and microwave lines [G. Wlodarczak, L. Martinache, J. Demaison, and B. P. Van Eijck, J. Mol. Spectrosc. 127, 200-208 (1988)]. A set of rotation parameters was determined for the ground state in Ir and IIIr representations, together with vibration-rotation constants for the v1 = 1 and v22 = 1 vibrational states. The fine structure in the strongest of the hot bands in that range was highlighted by division, from the experimental data, of the spectrum of the 22(1)0 band, computed using the vibration-rotation parameters. The rotational assignment of 930 lines in the strongest hot band was performed. The 22(1)024(1)1 vibrational assignment is proposed, leading to x22,24 = 1.90 cm-1. The transition dipole matrix element for the 22(1)0 band is estimated to || || = 2 x 10(-4) D. Copyright 1999 Academic Press.

From high-resolution infrared spectra of 14N12C12C14N, 14N13C13C14N, and 15N12C12C15N, we find that the levels 1000(0)0(0), 1000(0)1(1), 1000(0)2(0,2), and 1000(0)3(1,3) have very pronounced perturbations. Our analysis shows that these perturbations are due to a vibrational resonance among the levels 1000(0)0(0), 0102(0)2(0), and 0102(0)2(2) in the one case, and equivalent levels with one or more additional quanta of nu5 in the other three cases. The resonance constant for the perturbation involving nu1 is 0.25 cm-1. It has the dependence on v5 and l5 that is expected for the sextic potential constant, K124455, although it seems too large for such a high-order constant. The Deltal (or Deltak) = 2 interaction between, for instance, 1000(0)0(0) and 0102(0)2(2e) is shown to be primarily due to the l-type resonance mixing of the 0102(0)2(0) and 0102(0)2(2e) states. The resonance is nearly "turned off" for the 1000(0)2(0,2) and 1000(0)3(1,3) states of 14N13C13C14N because there are no level crossings between the interacting states and the band centers are too far away to have an obvious effect, although careful analysis shows that the perturbation can be seen in their effective centrifugal distortion constants. The spectrum of 15N12C12C15N shows level crossings only in the case of the 1000(0)1(1), 1000(0)2(0,2), and 1000(0)3(1,3) states. Copyright 1999 Academic Press.

The Raman spectrum of cyanogen 13C214N2 has been investigated at nearly Doppler resolution by means of a stimulated Raman technique. The regions around the bandheads of the nu1 (2260 cm-1) and nu2 (835 cm-1) vibrations have been recorded. Besides the fundamentals, hot bands arising from v5 = 1-3 and v4 = 1 have been observed. A number of strong perturbations have been detected. The spectra have been analyzed and rotational constants for the excited states have been obtained. Computer simulations of the Raman contours have been carried out as a test of the assignments. A few weak DeltaJ = -2 lines have also been observed in the nu1 region.

High-resolution (up to 0.0016 cm-1 unapodized) room temperature and collision-cooled (at approximately 100 K) mid-infrared (1000-1300 cm-1, 7.7-10 µm) absorption measurements of the nu3 and nu9 vibrational bands of difluoromethane (CH2F2, HFC-32) vapor were made with a Fourier transform spectrometer. A ro-vibrational analysis of over 900 infrared transitions has yielded quartic rotational constants, and the C-type Coriolis coupling xic39 = 0.28802(11) cm-1. The results are compared with a previous analysis [J. Matuszeski and M. Marshall, Spectrochim. Acta. A 52, 1069-1077 (1996)] of a jet-cooled spectrum. Copyright 1999 Academic Press.

The eigenstate-resolved, high-resolution (5 MHz) infrared spectrum of the asymmetric &dbond;CH2 hydride stretch of isobutene has been measured using an electric resonance optothermal spectrometer (EROS). This vibrational band near 3087 cm-1 was rotationally assigned with ground state microwave-infrared double-resonance spectroscopy. IVR rates from rotationally homogeneous IVR multiplets at values of total angular momentum, J ranging from J = 0 to J = 3 and Ka values of Ka = 0 to Ka = 2, were obtained. The average IVR lifetime for this vibrational mode is 105 ps and independent of rotational state. The experimental state density of the rotationless 000 vibrational state, approximately 150 states/cm-1, is in good agreement with the direct count result of 99 states/cm-1 using the C+3 v multiply sign in circle C-3 v (G36) molecular symmetry group. The lineshape profiles of the IVR multiplets are investigated in order to elucidate information concerning the dependence of IVR rates on the symmetry of the torsional wavefunction. We find that there is a common IVR rate among the various torsional symmetries. IVR lifetimes observed in the present study are compared to other asymmetric ethylenic hydride stretch IVR rates measured in our laboratory. Copyright 1999 Academic Press.

The pure rotational spectrum of the less stable conformer of methyl vinyl ether has been measured in an electric-resonance optothermal spectrometer. Analysis of the microwave spectrum shows that the less stable conformer is effectively planar with a low barrier between two gauche forms of the conformer. The rotational constants for the high-energy conformer, obtained from a least-squares fit to a threefold barrier internal rotation Hamiltonian are A = 39 192.490(26) MHz, B = 4527.5496(39) MHz, and C = 4181.2146(43) MHz. The threefold barrier to internal rotation is determined to be V3 = 427.516(71) cm-1. The dipole moment for the conformer has been measured using the Autler-Townes splitting of states in a strong, resonant microwave field. The dipole moment is µtot = 1.9(2) D [µa = 1.3(1) D, µb = 1.4(1) D]. The effectively planar structure of the conformer and the magnitude of the dipole moment are in good agreement with previous ab initio calculations. The experimentally determined threefold barrier to methyl rotation of the present study also agrees well with the value calculated from ab initio methods, 515 cm-1. Copyright 1999 Academic Press.

High-resolution vibration-rotation spectra of gas-phase deuterobromoacetylene have been recorded in the 240-990 cm-1 infrared region. The analyzed band systems are rich in hot bands and have a high density of lines. Five band systems and a total of 124 vibration-rotation bands of the isotopic species DCC79Br and DCC81Br have been rotationally analyzed. Accurate rotational parameters and vibrational wavenumbers for 33 vibrational states of each species have been obtained from the rotational analysis. l doubling and rotational l resonance have been observed on some states and the respective resonance parameters have been obtained through nonlinear least-squares optimization. A Fermi resonance block model with perturbation terms has been used for the analysis of the vibrational states. With optimized parameters, the model produces root-mean-square deviations of observed - calculated wavenumbers of about 0.3 cm-1 for both isotopic species. Copyright 1999 Academic Press.

Emission spectra have been recorded for hot water at temperatures up to 1550 degreesC. Separate spectra have been recorded in the 800-1900 and 1800-2500 cm-1 range. Assignments are made using a linelist generated from high accuracy, variational nuclear motion calculations, and energy differences. The spectra contain many hot bending transitions of the form (0n0)-(0n-10), where states up to n = 6 have been assigned. Detailed analysis shows that the spectra contain lines from 34 separate vibrational bands including other hot bending transitions and the difference bands (030)-(100), (110)-(020), (011)-(020), (100)-(010), (040)-(110), (040)-(011), (120)-(030), (012)-(030), (011)-(100), (110)-(001), and (101)-(110), all of which have not been observed previously. From a total of 8959 lines recorded, 6810 have been assigned; 4556 of these lines are new. These spectra represent the first detection of the (060) vibrational band, for which a band origin of 8870.54 +/- 0.05 cm-1 is determined. The (050) band origin is confirmed as 7542.40 +/- 0.03 cm-1. The assignments extend the range of J and Ka values observed for the bending states, particularly for (050) and (060), where 63 and 27 different rotational levels, respectively, have now been observed; 53 frequencies given in HITRAN are corrected. Copyright 1999 Academic Press.

The far-infrared spectrum of formamide (HCONH2) has been recorded at high resolution and over 9000 vibration-rotation lines assigned. Molecular parameters from the rovibrational analyses of the unperturbed 12(1)0 out-of-plane vibration band have been obtained for the ground state and the excited state. An analysis of the complicated resonance system between the 9(1)0, 11(1)0, and 12(2)0 bands has also been carried out. The mid-infrared spectrum of formamide has been recorded at low resolution and assignments for the fundamental, combination, and overtone bands in this region are given. The Large Amplitude Motion (LAM) of the out-of-plane mode has been reanalyzed using the new parameter set. Copyright 1999 Academic Press.

We have observed rotational transitions of propionitrile (C2H5CN) in the 8-200 GHz region and assigned 208 transitions with J

Line positions and line intensities of the nu1, nu3, and 2nu4 bands of 14NH3 were analyzed using line positions from 0.0054 cm-1 apodized resolution FT spectra recorded at Orsay and using line intensities from 0.011 cm-1 unapodized resolution FT spectra recorded at Kitt Peak National Observatory. About 2110 lines with J'

The Fourier transform gas-phase infrared spectra of the two lowest Coriolis-perturbed nu7 and nu9 bands of deuterated formic acid HCOOD and DCOOD have been measured with a resolution of ca. 0.003 cm-1. Combined analysis of the assigned IR transitions and all the available rotational data have allowed the determination of the band centers, rotational and centrifugal distortion parameters, and Coriolis coupling terms. Standard deviations of the IR transitions are 0.000246 cm-1 for HCOOD and 0.000209 cm-1 for DCOOD. Determined band centers are nu0(nu7) = 558.2723 cm-1, nu0(nu9) = 508.1321 cm-1 for HCOOD and nu0(nu7) = 554.4397 cm-1, nu0(nu9) = 492.2254 cm-1 for DCOOD. Copyright 1999 Academic Press.

Infrared spectra of a carbon dioxide sample enriched with oxygen-17 have been recorded with a resolution of about 0.0025 cm-1 in the region of the laser bands near 10 and 9 µm, using the long path difference Fourier Transform Spectrometer of the LPMA in Paris. The two laser bands of the 16O12C17O and 17O12C18O species have been analyzed for the first time. Line intensities for several isotopic species have been measured in this region and the rotationless transition dipole moments and Herman-Wallis coefficients of the corresponding bands have been reported. In particular intensities, alternation in the spectra of 17O12C17O has been analyzed. Copyright 1999 Academic Press.

The energy eigenvalue expression for a diatomic vib-rotor with the simple Kratzer potential De[(r - re)/r]2 {xmathmode}approximates poorly most of the anharmonic and rotation-vibration interaction terms, as shown by its expansion in a Dunham-type series and comparison with experimentally determined Dunham Yij coefficients. To correct this behavior, the expression was modified by terms dependent on the vibrational and rotational quantum numbers built directly into the formula. The formula thus modified turns out to be a useful alternative to the Dunham expansion for not-too-long progressions or sequences of rovibrational bands as it provides a precision of fit better or at least comparable to the Dunham series with the same number of adjustable parameters. Application of this modified energy expression to individual bands (such as fundamental bands) is shown to yield accurate estimates for equilibrium rotational constants Be and equilibrium internuclear distances re which are in many cases better than values obtained from standard power series analyses of single bands. Useful estimates are also obtained for the zero-order vibrational frequencies omegae and for the positions of the lower overtone or combination bands. Such information is otherwise not accessible from a conventional analysis of an individual band. Copyright 1999 Academic Press.

From the topological structures of the following classes of tetrahedral fullerenes-(1) Cn(h, h; -i, i), Cn(h, 0; -i, 2i), Cn(2h + i, -h + i; i, i), Cn(h - i, h + 2i; -i, 2i), and Cn(h, i; 0, i) for Td symmetry; (2) Cn(h, k; k, h), Cn(h, k; -h - k, k), and Cn(h, k; -h, h + k) for Th symmetry; (3) Cn(h, k; i, j) for T symmetry-we have obtained theoretically the formulas for the numbers of their IR and Raman active modes for all of the tetrahedral fullerenes through the decomposition of their nuclear motions into irreducible representations by means of group theory. Copyright 1999 Academic Press.

The rotational spectrum of bis(difluoromethyl) ether (CF2HOCF2H) has been observed and analyzed using both a conventional Stark-modulated microwave spectrometer and a pulsed molecular beam Fabry-Perot cavity microwave (FTMW) spectrometer. The lowest energy conformer studied here has a (hydrogen) syn-anti conformation. The high sensitivity of the FTMW spectrometer permits observation and analysis of the 13C, 18O, and 2H isotopomers in natural abundance. The electric dipole moment was measured for the normal species and found to be µa = 5.020(7) x 10(-30) C. m [1.505(2) D], µb = 0.19(4) x 10(-30) C. m [0.056(11) D], µc = 0.48(2) x 10(-30) C. m [0.144(7) D], and µT = 5.047(10) x 10(-30) C. m [1.513(3) D].

Rotational spectra of seven isotopomers of the weakly bound complex NeCO2, i.e., NeCO2, 22NeCO2, Ne13CO2, 22Ne13CO2, Ne18O13CO, Ne17OCO, and 22Ne17OCO, were measured using a pulsed molecular beam Fourier transform microwave spectrometer. Rotational and centrifugal distortion constants as well as the nuclear quadrupole coupling constants of 17O in Ne17OCO and 22Ne17OCO were determined. The obtained constants were used to derive structural and force field information. The parameters obtained are discussed, and compared with those of other, previously measured, rare gas-CO2 complexes. The 17O nuclear quadrupole coupling constants were analyzed and interpreted in terms of the angular anisotropy of the intermolecular potential energy surface. Copyright 1998 Academic Press.

The fine and hyperfine structure of the (0, 0) band of the B2Sigma+u-X2Sigma+g system of 14N+2 has been measured using fast-ion-beam laser spectroscopy. Rotational transitions with 0 /= 3, together with the complete rotational line profiles for N" < 5, were used to determine the spin-rotation constants and the Fermi and dipolar hyperfine constants for the B and X states. This is the first time the hyperfine constants for v" = 0 have been measured for gas-phase N+2. Copyright 1998 Academic Press.

A Dunham treatment of an effective Hamiltonian for diatomic molecules in 2Sigma states that includes contributions of the Born-Oppenheimer breakdown has yielded an expression for vibrational-rotational energy by an expansion in powers of (v + (1/2))i[N(N + 1)]j-k(N'/2)k, where N' is N for the J = N + (1/2) spin-doublet state and -(N + 1) for the J = N - (1/2) state and k = 0, 1, ellipsis, j. Analytic expressions for the expansion coefficients Y*vJijk provide a potential model appropriate for the spectral fits for molecules in 2Sigma states. The expansion coefficients Y*vJij0 for the k = 0 terms are exactly the same as the Y*vNij coefficients given for 1Sigma states, the Dunham coefficients Yij modified by the contributions of the Born-Oppenheimer breakdown, provided that a spin contribution originating from off-diagonal electronic corrections of the electronic part of the spin-orbit interaction can be ignored. Spin-rotation energy is given by the terms with coefficients Y*vJijk (k >/= 1). There are no Y*vJijk (k >/= 2) terms in the previously known methods of analysis for 2Sigma molecules. The present potential model is applied to the reported vibrational-rotational spectra of CaH and all spectral lines of 40CaH and 40CaD isotopomers are fitted to a single set of molecular constants simultaneously with significantly smaller standard deviations. Copyright 1998 Academic Press.

The Q-branch lines of pure HD were measured at densities ranging from 1 to 7 Amagat at 304.6 K. Each profile was fitted to the well-known Rosenkranz expression to extract the size of the asymmetry due to line mixing as well as to the linewidth. Line mixing and broadening coefficients were obtained by fitting the asymmetries and widths to a straight line as a function of gas density. Apart from a single existing measurement for the Q(0) line, our mixing coefficients are the first direct measurements of the asymmetry due to line mixing in HD. Our broadening coefficients are consistent with the best earlier measurements but are an order of magnitude more precise. Agreement is found with some existing semiclassical calculations of broadening. We have fitted our HD broadening coefficients to a variety of empirical energy gap laws. Our conclusions are that none of the exponential gap law (EGL), the modified exponential gap (MEG) law, and the statistical power gap (SPG) law successfully models our broadening coefficients. We present a modified version of the EGL and the MEG laws, which are successful in reproducing the experimental results. Using the fitted parameters of the new gap law, we have calculated the relaxation matrix of HD at room temperature. With this relaxation matrix, we have simulated the Q-branch spectrum at a number of densities between 49.1 and 490 Amagat and compared the results with previous high-density measurements. At all densities and frequencies, the simulated spectral intensity was found to agree with the measured strength within about 5% of the peak of the spectrum. In addition, the comparison provides evidence of a nonlinear vibrational dephasing shift in HD. Copyright 1998 Academic Press.

The pure rotational spectrum of AsD2 in the 2B1 ground electronic state was measured in the frequency region of 268-398 GHz by microwave spectroscopy. The AsD2 radical was generated in a free-space cell by dc-glow discharge of a gaseous mixture of D2 and He over arsenic powder. Fifty fine and hyperfine components of nine rotational transitions were measured and analyzed by least-squares methods determining the detailed molecular constants of AsD2: the rotational constants, the centrifugal distortion constants, the spin-rotation coupling constant with the centrifugal distortion terms, and the hyperfine coupling constants associated with the arsenic and deuterium nuclei. The harmonic force field of AsH2 was determined from the centrifugal distortion constants, the equilibrium vibrational frequency of nu2 mode of AsH2, and the inertial defects of AsH2 and AsD2. The harmonic force field was used to calculate vibrational corrections to the rotational constants of both species and thus the zero-point average structures for both species were derived; AsH2: rz(AsH) = 1.53436(15) Å, thetaz(HAsH) = 90.695(20) degrees, and AsD2: rz(AsD) = 1.52902(13) Å, thetaz(DAsD) = 90.722(17) degrees, where the errors in parentheses are due to residual inertial defects of the corrected moments of inertia. From the difference between the rz structures for AsH2 and AsD2 the re structure of AsH2 is estimated to be re(AsH) = 1.5158(6) Å, thetae(HAsH) = 90.79(8) degrees. Copyright 1998 Academic Press.

Fluorescence spectra of lanthanum monoiodide excited by the Ar+ 501.7-nm laser line have been observed and analyzed. Seven (sub)states are characterized. Preliminary rovibrational data are obtained for the four low-lying states (I-IV). The first two can be ascribed as X1Sigma and a3Delta: III does have Omega = 1, and IV is possibly 1Delta. The 11 laser-excited levels are tentatively grouped into three entities. Copyright 1998 Academic Press.

The intracavity laser spectroscopy (ILS) technique has been shown to be a very sensitive method for observing absorption spectra. By considering quantitative results (line-strengths and pressure broadening coefficients) obtained using the ILS method with a dye laser, the technique has been shown to provide quantitative information that is in excellent agreement with the values afforded by use of more traditional methods for acquiring absorption spectra. A similar investigation has been conducted for an ILS system based on a Ti:sapphire laser. Presented here are quantitative results for water vapor transitions occurring around 795 nm. Line intensities are determined as a function of water vapor pressure and effective path length (i.e., generation time). The line-strengths are compared with values determined by R. A. Toth [J. Mol. Spectrosc. 166, 176-183 (1994)] who used a multipass cell and the Fourier transform spectrometer at the Kitt Peak National Observatory. The good agreement between the results demonstrates that quantitatively accurate data can be obtained using the ILS technique with a Ti:sapphire laser. Copyright 1998 Academic Press.

Previously identified, measured, and rotationally assigned but unpublished J = 0-1 and 1-2 microwave a-dipole lines for excited states of the torsion for CH2DOH and CHD2OH are given torsional assignments for the first four excited states. The troublesome assignments were for the K-1 = 0 lines of the o2 state of CH2DOH and the e2 state of CHD2OH, where a resonance is found for the J0J levels. The assignment for these states was facilitated by combination differences with the b- or c-dipole intratorsional state transitions, relative intensities, and FIR combination differences for the e2 and e3 states of CH2DOH. A few new b- and c-dipole assignments are reported for o2 of CH2DOH and e2 of CHD2OH. Transitions for these two states have been analyzed to estimate the strength of the resonant interaction and energy difference for the levels involved and to estimate how well the theory is predicting the K-1-dependent torsional energy levels. The empirically determined DeltaB and DeltaC from nonrigidity for each species for the four excited states should prove helpful for future calculations of vibration-internal rotation-overall rotation interactions in these molecules. Copyright 1998 Academic Press.

The spectrum of TaS between 4000 and 20 000 cm-1 has been recorded in emission from a microwave discharge with a resolution between 0.011 and 0.025 cm-1. Seventeen electronic transitions have been rotationally analyzed. Fifteen of these have the ground state, 2Delta, as the lower state and two of them are transitions between excited states. The ground state has been fitted to a Hund's case (a) Hamiltonian. Effective molecular constants have been determined for the excited states, which are mainly described as Hund's case (c). Perturbations that have been found in the excited states are discussed. Transitions between states that are connected neither to the ground state nor to any of the other 14 electronic states of this work have been found. No analysis is presented for these transitions, but some of their characteristic features are described. Copyright 1998 Academic Press.

The Fourier transform infrared spectrum of SF6 was recorded in a supersonic expansion jet of an SF6/argon mixture. The SF6:Ar seeding ratio was 2:3. The instrumental bandwidth was 0.005 cm-1. A globar source and an MCT detector were used. A rotational temperature of approximately 30 K was achieved. The nu2 + nu6 combination band of 32SF6 was analyzed using a modified version of the spherical top data system (STDS) programs developed in Dijon. A very good fit was obtained for this band with an rms of 0.0036 cm-1. The effective Hamiltonian was developed up to fourth order for the nu2 + nu6 part, to second order for the nu2 and ground state parts, and to first order for the nu6 part. Five hundred twenty-one transitions were assigned, 40 of them reaching the F2u forbidden sublevel. The positions of the two F1u and F2u sublevels are found to be 991.276 and 989.487 cm-1, respectively. The nu3 band of the 33SF6 and 34SF6 isotopomers were also analyzed. Parameters and simulations are presented. A first detection of the nu3 Q branch of 36SF6 (0.02% natural abundance) is reported. Copyright 1998 Academic Press.

The A2Pi-X2Sigma+ Deltav = 0 sequence of BeD was observed in the 19 500-20 800 cm-1 spectral region using a Fourier transform spectrometer. The emission spectrum was excited in a Be hollow cathode discharge lamp with a He/D2 gas mixture. The observed lines were assigned to the 0-0 to 6-6 bands. The Deltav = -1 sequence was too weak to be seen in our Fourier transform spectra. We therefore used a previously recorded but unpublished arc emission spectrum to identify the 0-1 to 5-6 Deltav = -1 bands. Consequently, all of the diagonal bands could be linked together and the vibrational intervals determined. The Deltav = 0 and Deltav = -1 data were fitted together in a global fit and effective constants derived. Using the information available from the study of the C2Sigma+-X2Sigma+ system [R. Colin, C. Drèze, and M. Steinhauer, Can. J. Phys. 61, 641 (1983)], the v = 8-12 vibrational levels of the ground state were added in a Dunham fit. A set of Dunham Y constants was determined for the X2Sigma+ state along with traditional equilibrium parameters for the A2Pi excited state. The equilibrium bond lengths were found to be 1.341742(5) Å for the ground state and 1.33309(4) Å for the excited state. A reanalysis of the previously published A2Pi-X2Sigma+ 0-0 to 3-3 Deltav = 0 bands of BeT [D. De Greef and R. Colin, J. Mol. Spectrosc. 53, 455-465 (1974)] was also performed. Copyright 1998 Academic Press.

The complexes of SO3 with HF, HCl, and HBr have been studied by microwave spectroscopy. In all three systems, the halogen atom approaches the SO3 on or near its C3 axis, and the vibrationally averaged structure is that of a symmetric top. The S-X bond lengths are 2.655(10), 3.1328(57), and 3.2339(85) Å for the HF, HCl, and HBr complexes, respectively, and in all three systems the out-of-plane distortion of the SO3 is negligible. In HF-SO3, the hydrogen points away from the SO3 and hyperfine structure in the DF complex gives an average angle of 47.7 degrees with respect to the vibrationally averaged C3 axis of the complex. In the HCl and HBr complexes, however, the HX unit is nearly parallel to the SO3 plane. In HCl-SO3, the HCl forms a 72.8 degrees angle with the average C3 axis of the complex, with the proton tilting slightly toward the SO3. In HBr-SO3, the average orientation of the HBr is 73.0 degrees off the symmetry axis of the complex, but the direction of the tilt (toward or away from the SO3) is not determined. Although the hydrogen halides react with SO3 in bulk to produce halosulfuric acids, these gas-phase complexes are much like weakly bound dimers. Copyright 1998 Academic Press.

The high-resolution infrared bands centered at 769 and 1043 cm-1 for 1,2,4-triazine C3H3N3 have been analyzed, using the full asymmetric rotor Hamilton of Watson in A-reduced form using IIIr-representation. All the ground state rotation constants and three of the quartic centrifugal distortion constants could be determined with high precision from a simultaneous analysis of the two bands. The standard deviation of fit was 0.00077 cm-1. The upper state constants for the two bands have been determined with similar precision. The ground state rotational constants obtained from the present analysis are very similar to those predicted from the ab initio study of the equilibrium structure. This strongly suggests that the similarity in several of the ring bond lengths, predicted in the latter, is indeed real. Copyright 1998 Academic Press.

Rotational spectra of six isotopomers of the van der Waals dimer Ne-N2O, namely 20Ne-14N14NO, 22Ne-14N14NO, 20Ne-14N15NO, 22Ne-14N15NO, 20Ne-15N14NO, and 22Ne-15N14NO, were measured in the frequency range between 5 and 18 GHz using a pulsed beam cavity Fourier transform microwave spectrometer. The spectra are those of prolate asymmetric rotors and are in accord with a T-shaped structure of the complex. Both a- and b-type transitions were measured. Nuclear quadrupole hyperfine patterns of the rotational transitions due to the 14N nuclei were observed and analyzed. The rotational and centrifugal distortion constants were determined, as well as the quadrupole coupling constants chiaa and chibb, for both terminal and central 14N nuclei. The distance from the center of mass of the N2O subunit to the Ne atom and the angle between this distance and the N2O axis were derived from the rotational constants. The structural parameters indicate that the Ne atom is on average closer to the O atom than to the terminal N atom. Copyright 1998 Academic Press.

The N = 2-1 pure rotational transition of the ND radical (X3Sigma-) near 1 THz was measured with the Cologne terahertz spectrometer. The ND radical was produced in a dc discharge of a flowing mixture of deuterated ammonia and helium. Frequencies of five strong fine-structure transitions with associated hyperfine components were precisely measured and analyzed to determine a complete set of accurate molecular constants, e.g., the rotational and centrifugal distortion constants B0 = 263265.4735(45) MHz and D0 = 14.62876(74) MHz, together with the fine and hyperfine constants. Based on these constants, the rotational frequencies of ND up to 4 THz were predicted with the aim to guide future astronomical searches. For completeness we also include similar predictions for NH. Copyright 1998 Academic Press.

The SiH2D2 asymmetric top has nine vibrational modes, five of them forming a pentad strongly perturbed by Coriolis interactions. High-level ab initio calculations of SiH2D2 have been performed which yield numerous spectroscopic parameters related to the harmonic and anharmonic force fields. The bending pentad comprising nu4(A1), nu7(B1), nu5(A2), nu9(B2), and nu3(A1) has been studied by high-resolution Fourier transform spectroscopy; the region 600-1050 cm-1 has been investigated with a resolution of ca. 4 x 10(-3) cm-1. Raman BOXCARS spectroscopy has been used for the infrared inactive nu5 band. The Raman apparatus function was 0.0054 cm-1. Assignments of about 4000 transitions including all bands have been made, mostly employing ground state combination differences techniques, and a global fit has been performed. The fundamentals nu4 (681.624 cm-1), nu7 (742.640 cm-1), nu5 (842.381 cm-1), nu9 (859.750 cm-1), and nu3 (942.741 cm-1) are strongly coupled by A-, B-, and C-type Coriolis interactions, and ab initio predictions of these interaction parameters were used to set up a network of interactions that was refined by the experimental data. The global standard deviation for the entire body of data is 7.1 x 10(-4) cm-1. Satisfactory synthetic spectra which are very sensitive to relative signs of dipole moment derivatives and Coriolis interaction constants were obtained with the guidance of ab initio calculations. Finally, fair to good agreement of experimental and ab initio calculated molecular parameters was obtained. For the first time, a complete analysis of the pentad of SiH2D2 in the 10-16 µm region has been carried out. A full set of rovibrational parameters is given for these five interacting levels, including first and second order Coriolis interaction constants. Copyright 1998 Academic Press.

The absorption spectrum of methanol vapor has been recorded at room temperature from 3200 to 4200 cm-1 with a 1.24-M path-difference Fourier transform spectrometer. Over 10 000 transitions to the torsion-rotation states n, tau J, K of the OH stretching fundamental band nu1 have been assigned, thereby greatly expanding the results of previous investigations. Approximately 4000 of the cleaner lines have been used to determine 665 excited state torsion-rotation levels with principal torsional quantum number n = 0 as well as 494 levels with n = 1, 286 levels with n = 2, and 14 levels with n = 3. These levels correspond to 86 values of the quantum numbers n, tau, K. Most of the levels of a given n, tau, K are perturbed resulting in irregular P-, Q-, and R-branch series. The J = 0 origins for 64 values of n, tau, K have been fitted and a value of 410 cm-1 obtained for the hindering potential barrier. This is in agreement with a previous study of grating spectra but is lower than that obtained in more recent analyses of n = 0 <-- 0 transitions observed for K

The temperature dependence of lineshift and broadening of the rovibrational transitions R(18) and R(20) of the CO fundamental band, perturbed by Ar, N2, O2, and H2, have been measured with high frequency accuracy and at temperatures between 160 and 270 K in steps of 20 K. A wavelength stabilized tunable diode laser spectrometer has been combined with a low temperature long path cell of 134 m absorption length and 1 m basis length. For all measurements the CO pressure was below 0.1 mbar to avoid self-shift and self-broadening. In case of line broadening the temperature dependence is quite well reproduced by an exponential relation, b(T) = b(T0)(T/T0)-n. For all foreign gases, the exponent n has been obtained (0.53

A six-dimensional variational code, recently presented for the determination of the rovibrational energy levels of formaldehyde, has been used to refine a quartic potential surface of thioformaldehyde and simultaneously to optimize its geometry. The parameters have been adjusted to obtain as good agreement as possible with the known J = 0 vibrational energy levels and the corresponding observed J = 1 rotational lines of both H2CS and D2CS, where known. This is a highly nonlinear problem, and it is not possible to refine separately the geometry and force field. We have simultaneously optimized the HCS bond angle, the quadratic force field, and a partial cubic and quartic force field. Fermi and Coriolis resonances have been reproduced. The predicted geometry is CH = 1.0856 Å, CS = 1.6110 Å, HCS = 121.88 degrees. Predictions are made for overtones and combination bands of H2CS and D2CS. Furthermore, a prediction is made for the unobserved fundamental nu5 of D2CS, which lies very close to 3nu6. Copyright 1998 Academic Press.

Eight emission spectra of CO2 + N2 mixtures excited by dc discharge were recorded using a Fourier Transform Spectrometer (Bruker Spectrometer 120HR) with a resolution of 0.003 cm-1 in the 4.5-µm region. Results (wavenumbers, band centers, spectroscopic constants) concerning 13 new vibrational transitions which have not been observed earlier and which occur between highly excited levels (hence their very small population) are reported. The derived spectroscopic parameters allow the reproduction of the experimental wavenumbers with a RMS < 3 x 10(-4) cm-1. Copyright 1998 Academic Press.

The band absorbance and line absorbance of R branch transitions are obtained from high-resolution Fourier transform measurement of silane and germane local mode overtones (n000), n = 1-5, under proper sample pressures and absorption lengths. The absorption coefficients of these overtones are derived by linear least-squares fitting. The relative intensities of overtones can be satisfactorily reproduced with the bond dipole model containing two adjustable parameters. Copyright 1998 Academic Press.

Ar-broadening coefficients are measured for 29 lines of CH3F in the RQ0 and RQ6 branches of the nu6 band, using a tunable diode-laser spectrometer. The collisional widths obtained by fitting Rautian profiles to the measured shapes of the lines are significantly larger, especially for the overlapping lines at low-J values, than those obtained from Voigt profiles. The broadening coefficients for the lines belonging to the same low-J transitions (J = 7-10) appear to be greater in the RQ0 branch than in the RQ6 branch. Comparisons have been made with calculated results based on a semiclassical model including adjustable potential parameters. Copyright 1998 Academic Press.

The J = 1-0 to 4-3 spectral lines of SD+3 were measured in the 152-610 GHz region using a source-modulated microwave spectrometer. The SD+3 ion was generated in a free space absorption cell by a hollow-cathode discharge in a gas mixture of D2S and D2. The rotational constant B0 and the centrifugal distortion constants DJ and DJK were determined from the measured frequencies. A vibration-rotation analysis was carried out and the rz structures of SH+3 and SD+3 were derived from their zero point averaged rotational constants, expressed as SH+3: rz = 1.36512(22) Å and thetaz = 94.098(26) degrees, and SD+3: rz = 1.36086(16) Å and thetaz = 94.1211(195) degrees, where the difference between thetaz(HSH) and thetaz(DSD) was assumed to be the same as that between thetaz(HPH) of PH3 and thetaz(DPD) of PD3. From the shift between the rz structures of SH+3 and SD+3, the re structure of SH+3 was estimated to be re = 1.35001(113) Å, thetae = 94.181(135) degrees. Copyright 1998 Academic Press.

A total of 6071 transition wavenumbers of the nu2, nu3, nu5, and nu6 fundamental bands of H313CF and 1689 frequencies of the rotational transitions in the v2 = 1, v3 = 1, v5 = 1, and v6 = 1 vibrational states have been fitted simultaneously by taking into account various Coriolis interactions, l-type interactions, and alpha-resonance terms between and within the vibrational states. The standard deviation of the fit using 75 parameters was final sigma = 7.63 x 10(-5) cm-1 for the infrared data and 0.150 MHz for the rotational data. The possibility of obtaining a quantitative fit of the very precise data of high-resolution Fourier transform and submillimeter-wave spectroscopy for a semirigid symmetric top molecule is discussed. Copyright 1998 Academic Press.