An ab initio study of the molecular structure and vibration-rotation spectrum of the triplet radical HCCN |
| |
Authors: | Per -Åke Malmquist Roland Lindh Björn O. Roos Stephen Ross |
| |
Affiliation: | (1) Department of Theoretical Chemistry, Chemical Centre, University of Lund, P.O.B. 124, S-221 00 Lund, Sweden;(2) Department of Chemistry, University of Alberta, T6G 2G2 Edmonton, Alberta, Canada |
| |
Abstract: | The bent triplet cyanocarbene H-C-C N and the linear triplet allene H-C=C=N have been studied by the CASSCF and CI methods, using a DZP basis. Relaxation of all geometrical parameters for the CASSCF energy results in a bent molecule with CCH angle 133° and a barrier to linearity of 6.4 kcal/mol, which was lowered to 2.3 kcal/mol in a subsequent CI calculation. The Davidson correction lowered it further to 1.8 kcal/mol.A 26-term analytical potential energy surface (PES) was fitted to CASSCF, CI, and Davidson corrected CI energies in 94 different geometries. Using these three potentials, the semi-rigid bender model predicts a CCH bending frequency of 782, 505, and 503 cm–1, resp., which compares favourably with an experimentally observed IR transition line at 458 cm–1. For the deuterated species, the corresponding frequencies are 610, 407, and 402 cm–1, to be compared with two possible absorption lines at 405 and 317.5 cm–1.The PES was then parametrized by adding a variable CCH angle dependence, and a comprehensive vibration-rotation spectrum was calculated variationally, using the exact 4-atom vibration-rotation kinetic Hamiltonian, for a range of barrier heights. Comparison with experiment indicates a barrier in the range 1±0.5 kcal/mol.Dedicated to Professor J. Koutecký on the occasion of his 65th birthday |
| |
Keywords: | HCCN Vibration-rotation Potential energy surface |
本文献已被 SpringerLink 等数据库收录! |
|