@article {61395178,
title = {CASSCF-wave packet ab initio prediction of electronic and vibrational spectra: Application to the A({\^A}{\texttwosuperior}Pi) reverse arrow X({\^A}{\texttwosuperior}. sigma. /sup +/) absorption of C2H at 3000 K},
journal = {J. Chem. Phys.},
volume = {82},
year = {1985},
pages = {5064},
abstract = {The combination of a b i n i t i o calculation of electronic wave functions with a wave packet calculation of the nuclear motion is used, within the Born{\textendash}Oppenheimer approximation to compute the vibrational and electronic absorption of a polyatomic molecule. A particular virtue of this approach is that high as well as low temperature spectra are both calculable. This method is applied to C2H, for which the complete active space self-consistent field (CASSCF) method is used to determine full Born{\textendash}Oppenheimer potential surfaces. Using the assumption that the A(2Π) {\textleftarrow} X(2Σ+) absorption can be written as the sum of the A(2 A{\textquoteright}) {\textleftarrow} X and A(2 A{\textquoteleft}) {\textleftarrow} Xabsorptions, the spectra are determined to 60 cm- 1 resolution at a temperature of 3000 K. As a result of the large thermal bending amplitude at 3000 K, the calculated spectra are broad and have little resolved structure. Two bands are resolvable, one is due to the A(2 A{\textquoteleft}) {\textleftarrow} Xabsorption and is centered at 5500 cm- 1, while the other is due to A(2 A{\textquoteright}) {\textleftarrow} Xabsorption and is centered at 9500 cm- 1. The dramatic blue shift of the A(2 A{\textquoteright}) {\textleftarrow} X band results from the combination of the large X state thermal bending amplitude and high bending frequency of the A(2 A{\textquoteright}) state. We also determine the X state pure vibrational absorptionspectrum and show it to be of much lower intensity than the pure electronic spectrum.},
url = {http://dx.doi.org/10.1063/1.448628},
author = {J. R. Reimers and K. R. Wilson and E. J. Heller and S. R. Langhoff}
}