Solvation Dynamics in Water: 2. Energy Fluxes on Excited- and Ground-State Surfaces

This series' first installment introduced an approach to solvation dynamics focused on expressing the emission frequency shift (following electronic excitation of, and resulting charge change or redistribution in, a solute) in terms of energy fluxes, a work and power perspective. This approach, which had been previously exploited for rotational and vibrational excitation-induced energy flow, has the novel advantage of providing a quantitative view and understanding of the molecular-level mechanisms involved in the solvation dynamics via tracing of the energy flow induced by the electronic excitation's charge change or redistribution in the solute. This new methodology, which was illustrated for the case in which only the excited electronic state surface contributes to the frequency shift (ionization of a monatomic solute in water), is here extended to the general case in which both the excited and ground electronic states may contribute. Simple monatomic solute model variations allow a discussion of the (sometimes surprising) issues involved in assessing each surface's contribution. The calculation of properly defined energy fluxes/work allows a more complete understanding of the solvation dynamics even when the real work for one of the surfaces does not directly contribute to the frequency shift, an aspect further emphasizing the utility of an energy flux approach.