| Product state distributions for reactive and inelastic scattering in the simplest neutral bimolecular reaction, H + D2, have been measured as functions of collision energy. The experimental measurements employ the photoinitiated reaction technique with resonant enhanced multiphoton ionization (REMPI) detection. A mixture of HBr and D2 is supersonically expanded from a pulsed nozzle into a vacuum chamber. The HBr is photolyzed with a pulsed, tunable UV laser, and the collision energy can be altered by changing the laser wavelength. After a 20 ns delay in which single collisions occur, the inelastically scattered products D2(nu', j') or the reaction products HD((nu ',j') are state-selectively ionized via (2+1) REMPI. The ionized products are detected mass-spectrometrically, and the ion current is converted into a partial cross section for forming individual quantum states. Calibrations and correction factors, including measured and calculated values of the quantum state dependence of the REMPI line strengths, are discussed.; Rotational distributions have been measured for inelastically scattered products D2(nu' = 1, 2, j ') and for reaction products HD(nu' = 2, 3, j') in the collision energy range 1.3--1.9 eV. These measurements are analyzed quantitatively and qualitatively. In a quantitative sense, the experimental results are compared with full dimensionality quantum mechanical calculations on an accurate potential energy surface. Experiment and theory agree nearly quantitatively for inelastic scattering over the entire collision energy range in both vibrational manifolds. For reactive scattering, agreement is excellent in the lower vibrational manifold; in the higher vibrational manifold, however, the calculated distributions are systematically too cold, with the discrepancy becoming more pronounced at higher collision energy. Possible errors in the potential energy surface (the Born-Oppenheimer diagonal correction) and in the dynamical calculations (the geometric phase effect) are considered as causes for this disagreement.; In a more qualitative sense, trends in the state distributions are compared for reactive and inelastic scattering. In reactive scattering, the distributions are considerably hotter rotationally for higher collision energies and considerably colder rotationally in the higher vibrational manifold. In inelastic scattering, however, the trends are extremely weak and reversed in direction. With the aid of quasiclassical trajectory calculations, physical models of dynamics that might explain these results are discussed. |
