Single water solvation dynamics in the 4-aminobenzonitrile–water cluster cation revealed by picosecond time-resolved infrared spectroscopy

Abstract

The dynamics of a solvent is important for many chemical and biological processes. Here, the migration dynamics of a single water molecule is triggered by the photoionization of the 4-aminobenzonitrile–water (4ABN–W) cluster and monitored in real time by picosecond time-resolved IR (ps TRIR) spectroscopy. In the neutral cluster, water is hydrogen-bonded to the CN group. When this CN-bound cluster is selectively ionized with an excess energy of 1238 cm⁻¹, water migrates with a lifetime of τ = 17 ps from the CN to the NH₂ group, forming a more stable 4ABN⁺–W(NH) isomer with a yield of unity. By decreasing the ionization excess energy, the yield of the CN → NH₂ reaction is reduced. The relatively slow migration in comparison to the ionization-induced solvent dynamics in the related acetanilide–water cluster cation (τ = 5 ps) is discussed in terms of the internal excess energy after photoionization and the shape of the potential energy surface.