Determination of bond lengths of polyatomic species using vibrational frequencies

Abstract

Structural parameters of excited molecules and ions play a significant role in understanding the bonding nature and related properties of these species. In the present study, the modified Badger's and Hershbach and Laurie's equations, and the potential energy distribution (PED) method in the symmetry coordinate representation as proposed recently are applied to determine bond lengths of selected types of polyatomic molecules and ions in the form of A 2BC ( C 2v), A 2B 2 ( D ∞h), AB 2C ( C ∞ v ), A 4B 2 ( D ∞h) and A 6B 6 ( D 6h). These species include H 2CO, H 2CS, ClCS, C 2H 2, C 2F 2, C 2Cl 2, C 2Br 2, C 2I 2, C 2N 2, HCCCl, HCCBr, C 4H 2, C 4N 2 and C 6H 6. The results obtained compare favorably with experimental values and those from theoretical works of molecular orbital calculations and Franck-Condon analyses. The newly proposed methods require only a very small amount of observed data including vibrational frequencies of the two related electronic states and one of the two geometries. These algorithms are simple and fast in structure elucidation in contrast to other theoretical procedures.