Experimental and theoretical reaction cross sections for the H+HCl system

The dynamics of the gas-phase reaction of H atoms with HCl has been studied experimentally employing the laser photolysis/vacuum-UV laser-induced fluo rescence (LP/UV-LIF) "pump-and-probe" technique and theoretically by means of quasiclassical trajectory (QCT) calculations performed on two versions o f thr new potential energy surface of Bian and Werner [Bian. W.; Werner, H. -J, J. Chem. Phys. 2000, 112,220]. In the experimental studies translationa lly energetic ii atoms with average collision energies of E-col = 1.4 and 1 .7 eV were generated by pulsed laser photolysis of H2S and HBr at 222 nm, r espectively. Ground-state Cl(P-2(3/2)) and spin-orbit excited Cl*(P-2(1/2)) atoms produced in the reactive collision of the H atoms with room-temperat ure HCl were detected under single collision conditions by VUV-LIF, The mea surements of the Cl* formation spin-orbit branching ratio phi (Cl)* (1.4 eV ) = [Cl*]/[Cl + Cl*] = 0.07 +/- 0.01 and phi (Cl)*(1.7 cV) = 0 19 +/- 0.02 revealed the increasing importance of the nonadiabatic reaction channel H HCl --> H-2 + Cl* with increasing collision energy. To allow for compariso n with the QCT calculations, total absolute rractiun cross sections for chl orine atom formation, sigma (R)(1.4 eV) = (0.35 +/- 0.16) A(2) and sigma (R )(1.7 eV) = (0.13 +/- 0.06) Angstrom (2), have been measured using a photol ytic calibration method. In addition, further QCT calculations have been ca rried out for the H + DCl isotope reaction which can be compared with the r esults of previous reaction dynamics experiments of Barclay et al. [Barclay , V. J,; Collings, B, A.; Polanyi. J. C.; Wang, J. Ii. J. Phys. Chem. 1991, 95, 2921].