Regularities in the resonance Raman overtone spectrum from the third excited state of chrysene

Abstract

The frequency doubled 514 nm line of the argon laser at 257 nm is shown to fall exactly in the 0–1 absorption band of the third electronic absorption band of chrysene. Resonant Raman scattering from this vibronic state shows three strong Raman bands in the fundamental region (900–1700 cm−1) as well as bands in the overtone and combination region (2500–5000 cm−1). Only the fundamental at 1384 cm−1 shows overtone bands and it also shows combination bands with the other two. The intensity of all of the Raman bands as well as the absorption spectrum is calculated from vibronic theory on the assumption that one band (1384 cm−1) is greatly displaced in the excited state and the large Franck–Condon factors from this band helps to enhance the intensity of the other two bands which are only slightly displaced. Since the third electronic state wave function has a single node which divides the long axis of the molecule, it is suggested that the 1384 cm −1 vibration also has a single node and thus the vibration is a longitudinal stretching of the chrysene molecule.