Ab initio calculation of a global potential, vibrational energies, and wave functions for HCN/HNC, and a simulation of the A-tilde-X-tilde emission spectrum
Abstract
We present a potential energy surface for the HCN/HNC system which is a fit to extensive, high quality ab initio, coupled-cluster calculations. The new surface is an improved version of one that was reported previously by us [J. A. Bentley, J. M. Bowman, B. Gazdy, T. J. Lee, and C. E. Dateo, Chem. Phys. Lett. 198, 563 (1992)]. Exact vibrational calculations of energies and wave functions of HCN, HNC, and delocalized states are done with the new potential using a new method, which combines a truncation/recoupling method in a finite basis representation procedure with a moveable basis to describe the significant bend-CH stretch correlation. All HCN and HNC states with energies below the energy of the first delocalized state are reported and characterized. All delocalized states up to 18 347 cm-1 above the HCN zero-point energy and higher energy localized HCN states are also reported and characterized. Vibrational transition energies are compared with all available experimental data on HCN and HNC, including high CH-overtone states up to 23 063 cm-1. We also report a simulation of the ÖX∼ stimulated emission pumping (SEP) spectrum, and compare the results to experiment. The simulation is performed within the Franck-Condon approximation, and makes use of 400 even-bend wave functions for the ground electronic state, and a realistic vibrational wave function for the first excited bend state in the excited à state. The potential for the à state is slightly modified, relative to one implied by a previously reported force field, to improve agreement with the experimental fundamentals for the à state. In addition, the Östate wave function is adjusted slightly to improve agreement with the SEP spectrum. We also report Franck-Condon factors for odd bending states of HCN, with one quantum of vibrational angular momentum, in order to compare with the recent assignment by Jonas, Yang, and Wodtke [J. Chem. Phys. 97, 2284 (1992)], based on axis-switching arguments of a number of previously unassigned states in the SEP spectrum.
- Publication:
-
Journal of Chemical Physics
- Pub Date:
- July 1993
- DOI:
- 10.1063/1.465809
- Bibcode:
- 1993JChPh..99..308B
- Keywords:
-
- Emission Spectra;
- Hydrocyanic Acid;
- Vibrational Spectra;
- Wave Functions;
- Angular Momentum;
- Electron Transitions;
- Franck-Condon Principle;
- Molecular Structure;
- Potential Energy;
- Quantum Chemistry;
- Atomic and Molecular Physics