Solvent effects are important for understanding solution-phase chemical reactions, but solvent dynamics and the way they couple to solutes can change during the course of the reaction. Surprisingly, very few studies have explored how solvent effects can change during the course of a reaction that explores a wide range of solvent configurations, such as solution-phase bond-breaking and bond-formation. This study explores solvent dynamics during the course of a bond-breaking reaction, focusing on the photodissociation of Na2+ in liquid Ar as a paradigm system for which the solute chemical bond can be treated quantum mechanically. We find that the solvent dynamics shows two discrete changes when the solute atoms are 6.0 Å (100 fs after excitation) and 7.0 Å (170 fs after excitation) apart as a result of caging and the degeneracy between electronic states, respectively. We also find that the solvent dynamics immediately following excitation are driven by relative Ar motions both above and parallel to the bond-axis as a result of the rapidly dissociating dimer, something that is an entirely quantum mechanical effect. Our results show that the dissociating molecule can encounter discrete changes in solvent environment and that these fluctuations cause nonequilibrium dynamics to differ greatly from those seen at equilibrium.

Discrete changes in solvent dynamics in the bond-breaking of Na2+ in liquid Ar via photodissociation

ACS Spring 2022

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