Imaging H abstraction dynamics in crossed molecular beams: Cl + ROH reactions

Abstract

The crossed beam reactions of ground state Cl(²P_3/2) atoms with alcohols (CH₃OH, C₂H₅OH and 2-C₃H₇OH) have been studied using the technique of velocity map imaging (VELMI). The corresponding hydroxyalkyl radical was detected via single photon ionization using 157 nm laser light. The double differential cross sections were obtained at collision energies of 8.7 kcal mol⁻¹ for methanol, 6.0 and 9.7 kcal mol⁻¹ for ethanol and 11.9 kcal mol⁻¹ for 2-propanol. In all cases, the scattering was predominantly in the backward–sideways direction suggesting direct rebound dynamics, with varying amounts of sideways scattering. In the case of methanol, the angular distributions were predominantly in the sideways–backward direction with respect to the incoming alcohol beam. Scattering was into the backward hemisphere at the lower collision energy for ethanol, with enhancement of sideways scattering with an increase in collision energy. Isopropanol gave scattering predominantly in the backward direction. Coupling between the translational energy and angular distributions was particularly significant for ethanol at the lower collision energy. All of the translational energy distributions peaked at about 6 kcal mol⁻¹ and on average 30–40% of the available energy was deposited into product translation for all the alcohols studied. These results are contrasted with previous H abstraction studies performed on Cl–hydrocarbon systems.