B.A. 1967, Connecticut
M.S. 1968, Ph.D. 1972, Yale
Postdoctoral Fellow, 1972-73, Harvard
Visiting Professor, 1982-83, MIT
Collision dynamics of electronic energy transfer
We are studying collisions of metastable (electronically excited) neon, argon, krypton, and xenon atoms with water molecules in a molecular beam apparatus. The total quenching cross sections are measured by suitable monitor reactions that isolate individual electronic states of the metastable atoms, a new technique pioneered in our laboratory. The energy-dependent quenching cross section provides insight into the nature of the long-range forces between excited atoms and ground-state molecules. For reactions that produce luminescent products, we obtain the energy-dependent product formation cross sections as well. Comparison of the formation cross section with the total quenching value reveals details of the strength of the nonadiabatic interaction that gives rise to a specific energy transfer channel. The vibrational and rotational distribution of the fluorescing fragment is obtained by higher resolution spectral measurements. Geometric features of the excited potential energy surface on which the reaction occurs are inferred from the observed internal energy distribution.
A plot of the quenching cross section for Ar* colliding with water molecules vs. relative velocity is shown in the below figure.
plot of the quenching cross sectionSimple inverse power fits are given for each data set. For Ar*(J=2) at low velocities, the observed power (0.713) is close to that predicted by the orbiting model (0.667) based on a long-range r to the minus 6 potential. At high velocities, the cross sections flatten as seen by extrapolation of the low velocity fit. The J=0 cross sections are lower than J=2, which is very unusual. The J=0 state is higher in energy and normally more easily quenched. The nature of the long-range correlation of potential curves to the J=2 and J=0 states of Ar* with water may explain this behavior. The velocity range for J=0 is restricted because of a limitation in the monitor method for Ar*. The data were obtained by Don Mueller.
Absolute Quenching Cross Section for Collisions Between Ar(3P2,0) and H2O J. Chem. Phys. 89, 7031-7033 (1988) Stephen Novicki and John Krenos
Molecular Beam Study of the Ne*(3s3P2,0) + O2(X3Σg-) Reaction: Absolute Quenching and O*(3p5P, 3p3P) Product Cross Sections J. Phys. Chem. 97, 2106-2112 (1993) Don Mueller and John Krenos
Molecular Beam Study of the Collisions of State-Monitored, Metastable Noble Gas Atoms with O2(X3Σg-) J. Chem. Phys. 106, 3135-3145 (1997) Dawn Rickey and John Krenos
Study Guide for Atkins and Jones's Chemical Principles: The Quest for Insight W. H. Freeman and Company, New York, 1999, 450 pages John Krenos and Joseph Potenza
Book Review of Chemical Kinetics and Reaction Dynamics, by P. L. Houston J. Chem. Educ. 78, 1466 (2001) John Krenos
Study Guide for Atkins and Jones's Chemical Principles: The Quest for Insight Second Edition, W. H. Freeman and Company, New York, 2001, 476 pages John Krenos and Joseph Potenza
Reaction of Metastable Ar*(3P2) and Kr*(3P2) Atoms with Water Vapor: Excitation Functions for Electronic Quenching Collisions J. Phys. Chem. B 106, 8142-8147 (2002) Don R. Mueller and John Krenos
Book Review of Why Chemical Reactions Happen, by J. Keeler and P. Wothers J. Chem. Educ. 81, 201-202 (2004) John Krenos
Study Guide for Atkins and Jones's Chemical Principles: The Quest for Insight Third edition, W. H. Freeman and Company, New York, 2004, 750 pages John Krenos and Joseph Potenza (Includes a Solutions Manual)
Study Guide for Atkins and Jones's Chemical Principles: The Quest for Insight Fourth Edition, W. H. Freeman and Company, New York, 2007, 799 pages John Krenos and Joseph Potenza (Includes a Solutions Manual)
Book Review of Physical Chemistry (four volumes) I. Thermodynamics, II. Statistical Mechnaics, III. Kinetics, and IV. Quantum Mechanics, by H. Metiu J. Chem. Educ. 85, 206-207 (2008) John Krenos
Improving Student Success in University General Chemistry: Results of a New Chemistry Placement Program Proceedings of the ChemEd 2009 Conference Radford University Press, Abstract, page 96 (2009) John Krenos, Joseph Potenza, Donald Siegel, and Lewis Hirsch