Laser Stimulation andObservation of Simple GasPhase Radical Reactions

Abstract

Experiments on the effect of selective vibrational, translational and orientations excitation of reactants in bimolecular reactions can give important insights into the microscopic dynamics of elementary chemical reactions. The information obtained in such experiments can be compared with the results of theoretical calculations of the reaction dynamics based on ab initio potential energy surfaces and is also of basic interest to improve the kinetic data used in detailed chemical kinetic modelling. Rotational and vibrational energy transfer between H2 and H0 has been studied directly using Raman excitation combined with time resolved CARS spectroscopy. The competition between reactive and inelastic channels was investigated for reactions of atoms with vibrationally excited H2 and HCI molecules. Selective vibrational excitation was achieved by using infrared laser or Raman-pumping. The reaction products were detected by time resolved atomic line resonance absorption mass-spectrometry and CARS-spectroscopy. Insome cases information on the contributions of adiabatic and non-adiabatic reactive pathways could be obtained. The reaction H + O2-OH + O has been studied using translationally hot H atoms at various energies. Absolute total reactive cross-sections, nascent rotational state distributions and information on the distribution of orientations of the OH angular momentum vector using polarized dissociation and analysis laser sources have been obtained.