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The Singlet–Triplet Separation in CF 2 : State‐of‐the‐Art Ab Initio Calculations and Franck–Condon Simulations Including Anharmonicity
Author(s) -
Chau Footim,
Mok Daniel K. W.,
Lee Edmond P. F.,
Dyke John M.
Publication year - 2005
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200500114
Subject(s) - anharmonicity , chemistry , singlet state , ab initio , wave function , atomic physics , ab initio quantum chemistry methods , potential energy , triplet state , molecular physics , physics , excited state , quantum mechanics , molecule , organic chemistry
Geometrical parameters, vibrational frequencies and relative electronic energies of the X̃ 2 B 1 state of CF 2 − and the X̃ 1 A 1 and ã 3 B 1 states of CF 2 have been calculated. Core‐electron effects on the computed minimum‐energy geometries and relative electronic energies have been investigated, and relativistic contributions to the computed relative electronic energies calculated. Potential energy functions of the X̃ 2 B 1 state of CF 2 − and the X̃ 1 A 1 and ã 3 B 1 states of CF 2 have been determined, and anharmonic vibrational wavefunctions of these states calculated variationally. Franck–Condon factors including anharmonicity and Duschinsky rotation have been computed and used to simulate the ã–X̃ emission spectrum of CF 2 determined by S. Koda [ Chem. Phys. Lett. 1978 , 55 , 353] and the 364 nm laser photodetachment spectrum of CF 2 − obtained by R. L. Schwartz et al. [ J. Phys. Chem. A 1999 , 103 , 8213]. Comparison between theory and experiment shows that the theoretical approach benchmarked in the present study is able to give highly reliable positions for the CF 2 (X̃ 1 A 1 )+ e ←CF 2 − (X̃ 2 B 1 ) and CF 2 (ã 3 B 1 )+ e ←CF 2 − (X̃ 2 B 1 ) bands in the photoelectron spectrum of CF 2 − and a reliable singlet–triplet gap for CF 2 . It is therefore concluded that the same theoretical approach should give reliable simulated CCl 2 (X̃ 1 A 1 )+ e ←CCl 2 − (X̃ 2 B 1 ) and CCl 2 (ã 3 B 1 )+ e ←CCl 2 − (X̃ 2 B 1 ) bands in the photodetachment spectrum of CCl 2 − and a reliable singlet–triplet gap for CCl 2 .