Improvements in a Curvilinear Internal Coordinate Model for the CH Stretching and Bending Vibrations in Trihalomethanes

✍ Scribed by E. Kauppi

• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 451 KB
• Volume: 167
• Category: Article
• ISSN: 0022-2852
• DOI: 10.1006/jmsp.1994.1238

✦ Synopsis

The interactions between the (\mathrm{CH}) stretching and bending vibrations in (\mathrm{CH} X_{3})-type symmetrictop molecules have been studied. The previous curvilinear internal coordinate vibrational Hamiltonian (E. Kauppi and L. Halonen, J. Chem. Phys. 90, 6980-6992, 1989) has been improved by including contributions arising from the nonlinearity of the redundancy relation between the curvilinear internal coordinates. This affects the anharmonic kinetic energy terms of the pure (\mathrm{CH}) bending Hamiltonian. Vibrational energy levels have been calculated variationally. The model has been applied to data for (\mathrm{CHF}{3}, \mathrm{CHCl}{3}, \mathrm{CHBr}{3}), and (\left(\mathrm{CF}{3}\right){3} \mathrm{CH}). The potential energy parameters have been optimized by a nonlinear least-squares method using vibrational term values as data. In the cases of (\mathrm{CHF}{3}, \mathrm{CHCl}{3}), and (\mathrm{CHBr}{3}) data for both ({ }^{12} \mathrm{C}) and ({ }^{13} \mathrm{C}) isotopomers have been treated with one set of isotope invariant potential energy parameters. Good fits have been obtained by using five or six adjustable parameters. The values for the quartic bending force constants change considerably from the values obtained by ignoring the nonlinear redundancy contributions.

(c) 1994 Academic Press, Inc.