We present a rigorous and comprehensive theoretical treatment of the vibrational dynamics of benzene–H₂O and benzene–HDO dimers, where the quantum bound-state calculations of the coupled intra- and intermolecular vibrational states of the dimers are complemented by the quantum simulations of their infrared (IR) and Raman spectra utilizing the computed eigenstates. Apart from taking benzene to be rigid, the methodology for the nine-dimensional (9D) vibrational quantum calculations introduced in this study is fully coupled. The approach yields the intramolecular vibrational fundamentals and the bend (ν₂) overtone of H₂O and HDO in the complex, together with the low-lying intermolecular vibrational states in each of the intramolecular vibrational manifolds considered. Following the recently introduced general procedure [P. M. Felker and Z. Bačić, J. Chem. Phys. 151, 024305 (2019)], the full 9D vibrational Hamiltonian of the dimer is divided into a 6D intermolecular Hamiltonian, a 3D intramolecular Hamiltonian, and a 9D remainder term. A 9D contracted product basis is constructed from the low-energy eigenstates of the two reduced-dimension Hamiltonians, and the full vibrational dimer Hamiltonian is diagonalized in it. The symmetry present in the dimers is exploited to reduce the Hamiltonian matrix to a block diagonal form. Guided by the findings of our earlier study referenced above, the 6D intermolecular contracted bases for each symmetry block include only 40 eigenstates with energies up to about 225 cm⁻¹, far below the stretch and bend fundamentals of H₂O and HDO, which range between 1400 cm⁻¹ and 3800 cm⁻¹. As a result, the matrices representing the symmetry blocks of the 9D Hamiltonian are small for the high-dimensional quantum problem, 1360 and 1680 for the H₂O and HDO complexes, respectively, allowing for direct diagonalization. These calculations characterize in detail the H₂O/HDO intramolecular vibrations, their frequency shifts, and couplings to the large-amplitude-motion intermolecular vibrational sates. The computed IR spectra of the two complexes in the OH-stretch region, as well as the intermolecular Raman spectra, are compared to the experimental spectra in the literature.

中文翻译：

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苯-H2O和苯-HDO：使用紧凑型碱基的柔性H2O / HDO分子内振动激发和二聚体的分子间状态及其红外和拉曼光谱的全九维量子计算

我们对苯-H ₂ O和苯-HDO二聚体的振动动力学进行了严格而全面的理论处理，其中，二聚体的分子内和分子间耦合振动态的量子束缚态计算与分子间的量子模拟相辅相成。利用计算出的本征态获得其红外（IR）和拉曼光谱。除了将苯定为刚性以外，本研究中介绍的九维（9D）振动量子计算方法是完全耦合的。该方法产生的分子内振动基本面和弯曲（ν ₂的1H）泛音₂复合物中的O和HDO，以及所考虑的每个分子内振动歧管中的低层分子间振动状态。遵循最近引入的一般程序[PM Felker和Z.Bačić，J。Chem。物理 151，024305（2019）]，将二聚体的完整9D振动哈密顿量分为6D分子间哈密顿量，3D分子内哈密顿量和9D剩余项。从两个降维哈密顿量的低能本征态构造9D合同乘积基础，并且将完整的振动二聚体哈密顿量对角化。利用二聚体中存在的对称性将汉密尔顿矩阵简化为块对角线形式。根据我们前面引用的我们先前研究的结果，每个对称块的6D分子间收缩碱基仅包含40个本征态，能量高达225 cm ^-1，远低于H ₂ O和HDO的拉伸和弯曲基本能在1400 cm ^-1和3800 cm之间^-1。结果，代表9D哈密顿量对称块的矩阵对于高维量子问题较小，对于H ₂ O和HDO络合物则分别为1360和1680 ，从而允许直接对角化。这些计算详细描述了H ₂ O / HDO分子内振动，它们的频率偏移以及与大幅度运动分子间振动状态的耦合。将OH拉伸区中两种络合物的计算红外光谱以及分子间拉曼光谱与文献中的实验光谱进行了比较。