Determination of 0–0-Transition Frequencies from Diffuse Vibronic Spectra

Abstract

The equality of the probabilities of direct and inverse vibronic transitions between the initial and final elementary quantum Franck–Condon states in the adiabatic approximation is taken as the equality of the probabilities of one electronic transition in which only the initial and final elementary vibrational ensembles exchange places. The transition frequencies will have mirror symmetry with respect to the 0–0-transition frequency ν0. Accounting for this and selecting hot molecules in the anti-Stokes regions with the initial state in thermal equilibrium leads to a restoration of the known relation for the transition cross sections σ(ν) in the form [σ(ν)/ν] exp (±hν/2kT) = 𝜑[(ν – ν0)2], where ″+″ denotes emission; ″–″, absorption. Examples of using the relation to determine ν0 from absorption, fluorescence, and phosphorescence spectra are given and compared with ν0 obtained by jet-cooling.