Infrared Laser-Induced Heterogeneous Reactions: Fluence-dependent Branching Ratios in 2-Propanol with CuO

Abstract

The heterogeneous decomposition of 2-propanol vapor in the presence of CuO solid can be induced by irradiation with a pulsed CO2 laser. The reaction produces both propene and acetone. In contrast, the homogeneous multiphoton-induced decomposition of 2-propanol vapor yields only propene. The branching ratio ([hydrocarbon]/[acetone]) in the heterogeneous experiments has been examined as a function of laser pulse energy. While the yield of acetone increases monotonically with increasing fluence, yields of hydrocarbon show two distinctly different regimes of fluence dependence. Reactions have been run with both d8 and h8 2-propanol and on 1:1 mixtures. Neither reaction channel shows significant isotopic selectivity over a range of experimental conditions. This data will be discussed in light of a model that involves energy deposition in the solid, followed by either heterogeneous reaction of adsorbed material or energy transfer and subsequent multiphoton excitation of the alcohol vapor.