Dynamics of the H+HCl gas-phase reaction: absolute reactive cross-section for Cl(2P3/2) atom formation

The reaction of atomic hydrogen with HCl was studied in the gas phase using the laser photolysis/vacuum–UV laser-induced fluorescence (LP/VUV–LIF) `pump-and-probeʹ technique. Translationally energetic H atoms with an average energy of Ecm=1.0 eV in the (H–HCl)–center-of-mass system were generated by laser photolysis of H2S at 248 nm. Doppler profiles of nascent Cl(2P3/2) atoms produced in the reactive collision of the H atoms with room temperature HCl molecules were measured under single collision conditions by VUV–LIF. For the H+HCl→H2+Cl(2P3/2) reaction an absolute reaction cross-section σR(1.0 eV)=(0.34±0.05) Å2 was determined by means of a photolytic calibration method using the 248 nm laser photolysis of PCl3 as reference for well-defined concentrations of Cl atoms. Small amounts of Cl in the (2P1/2) excited state were observed in the H+HCl experiments. An upper limit of (0.02±0.01) Å2 was measured for the Cl∗(2P1/2) formation cross-section in the H+HCl reaction at 1.0 eV.