Theoretical Calculations on Vibrational Frequencies and Absorption Spectra of S1 and S2 States of Pyridine

Abstract

AbstractThree harmonic potential‐energy surfaces of 1A1, 1B1, and 1B2 singlet states of pyridine have been obtained by using ab initio method. Geometric properties and force fields of these states have been determined with the complete‐active‐space self‐consistent‐field (CASSCF) theoretical method. Vibrational frequencies of two excited states have been assigned on the basis of the potential energy distribution from normal mode analysis. The resulting properties are used to simulate the experimental absorption spectrum. From the spectral simulation the totally symmetric vibrations with large Huang‐Rhys factors have been identified as ν12 and ν6a modes in the 1B1 state; ν1 and ν12 modes in the 1B2 state, indicating that these modes have strong vibronic coupling between ground and excited states.