Measurement of the HD(v '=2,J '=3) product differential cross section for the H+D-2 exchange reaction at 1.55 +/- 0.05 eV using the photoloc technique

We describe a time-of-flight apparatus that uses core extraction to determi ne nascent product laboratory velocity distributions from which differentia l cross sections may be deduced. We emphasize the characterization of the i nstrument, the reaction conditions, and the calibration procedure. For this purpose, we have measured H-atom velocity distributions from HBr photolysi s, as well as the H-2(v(')=4,J(')=1) velocity distribution arising from the H+HBr reaction under quasi-monoenergetic collision conditions at 1.9 eV. C ollisional energy spread and reagent internal state distributions were dete rmined from the rotational and translational temperatures of the HBr photol ytic precursor and the D-2 diatomic reagent. The differential cross section for H+D-2-->HD(v(')=2,J(')=3)+D at 1.55+/-0.05 eV is presented and found t o peak near 145 degrees+/-10 degrees with an approximate full width at half maximum (FWHM) of 40 degrees. (C) 1999 American Institute of Physics. [S00 21-9606(99)00724-2].