Ultrafast dynamics of acetone–water clusters: the influence of solvation

Abstract

The ultrafast dynamics of acetone clusters and mixed clusters of acetone and water have been investigated using the pump-probe technique employing a femtosecond laser system coupled to a reflectron time-of-flight mass spectrometer. Studies using an excitation wavelength of 407 nm have revealed that solvation by both acetone and water molecules has a pronounced influence on the dynamics of acetone excited to the 5d Rydberg state. The lifetime of the excited acetone moiety was found to increase substantially from <100 fs in the case of the acetone molecule to a few picoseconds for both pure acetone and mixed acetone–water clusters. The significant slowing of acetone photodissociation is discussed as a possible influence on the lifetime of atmospheric acetone and it is concluded that the number density of acetone water complexes is too low to alter the overall photolysis rate of tropospheric acetone. However, at higher altitudes, where temperatures are lower, complex solvated acetone may become a more significant factor.