The Brownian Oscillator Model for Solvation Effects in Spontaneous Light Emission and Their Relationship to Electron Trans fer

The Brownian oscillator model for the coupling of solvent motions to a solute’s electronic transitions is applied to the calculation of absorption, relaxed fluorescence, and unrelaxed total emission (Raman and fluorescence) band shapes of a diatomic molecule in solution. The band shapes and the ratios of sharp scattering to broad fluorescence are explored as a function of the laser detuning from resonance, the parameters describing the solvent oscillator, and the excited-state lifetime, and direct comparisons with the stochastic theory, which does not contain the solvent-induced Stokes shift, are made. The relationship between the optical band shapes and the nuclear FranckCondon factor for nonphotochemical electron transfer processes is also discussed within the Brownian oscillator model for the solvation coordinate. The limits of applicability of the “high-temperature” limit for the Brownian oscillator are established.