NORMAL COORDINATE ANALYSES OF SIX ELECTRONICALLY EXCITED NON-LINEAR $XY_{2}$ MOLECULES.

Author Institution: Thermodynamics Research Center, Department of Chemistry Texas A \& M UniversityFor most of the electronically excited non-linear triatomic molecules, the antisymmetric stretching frequencies are not observed. In order to predict the molecular force fields and the unobserved fundamental frequencies, a normal coordinate treatment has been carried out for certain electronically excited bent triatomic molecules; namely, $H_{2}O(^{1}B_{1}), D_{2}O(^{1}B_{1}), ClO_{2}(^{2}A_{2}), SO_{2}(^{2}B_{1}, ^{1}B_{2}, ?), SO^{18}_{2}$ $(^{1}B_{2})$. The FG matrix method employing the most general quadratic potential function of the valence force type was used. The technique of separation of high and low frequencies was used for the $XO_{2}$ type molecules; but the calculated $F_{11}$'s were corrected using the following relation developed for the ground state species: $\% error = 10.2092 (G_{ts}G^{-1}_{ss}G_{s't'})+3.2094.$ The two main and two cross-term potential constants for all these molecules were determined. The bond stretching constants were fixed by comparison with the reliable data for corresponding diatomic molecules in the ground and excited states and triatomic molecules in the ground states. In turn the antisymmetric stretching frequenceies ($cm^{-1}$) for these molecules were predicted. They are as follows: $H_{2}O(^{1}B_{1})-3258; D_{2}O(^{1}B_{1})-2389; ClO_{2}(^{2}A_{2})-769; SO_{2}(^{2}B_{1})-1315; SO_{2}(^{1}B_{2}-1108; SO_{2}(?)-1219; SO^{18}_{2}(^{1}B_{2})-1061; NO_{2}(^{2}B_{2})-1083$