Reaction of Rb(5(2)D, 7(2)S) with H-2

The nascent quantum state distributions of the RbH product resulting from t he reaction of Rb(5(2)D(3/2,5/2), 7(2)S(1/2)) with H-2 are determined using a laser pump-probe technique. For the three investigated reactions, the na scent RbH product molecules are found to populate the lowest three vibratio nal (upsilon = 0, 1, and 2) levels of the ground electronic state. The rela tive vibrational populations an determined to be (0.42, 0.31, 0.27) for the Rb(5(2)D(3/2)) + H-2 reaction, (0.42, 0.33, 0.25) for the Rb(5(2)D(5/2)) H-2 reaction, and (0.45, 0.32, 0.23) for the Rb(7(2)S(1/2)) + H-2 reaction , each corresponding to a high vibrational temperature. The nascent RbH rot ational temperatures are found to be slightly below the cell temperature. B y comparing the spectral intensities of the RbH action spectra with those o f pertinent Rb atomic fluorescence excitation spectra, the relative reactiv ity with H-2 for the three studied atoms is in an order of Rb(7(2)S(1/2)) > Rb(5(2)D(3/2)) > Rb(5(2)D(5/2)). The relative fractions ([fv], [f(R)], [f( T)]) of average energy disposal are derived as (0.17, 0.04, 0.79) for the R b(5(2)D(5/2)) case, (0.17, 0.04, 0.79) for the Rb(5(2)D(5/2)) case, and (0. 14, 0.03, 0.83) for the Rb(7(2)S(1/2)) case, all having a major translation al energy release and a minor rotational energy release. All of the above r esults support the assumption that the Rb*-H-2 reaction occurs primarily in a collinear C-infinity upsilon collision geometry by a harpoon mechanism, in which the crossing between the ionic Rb+H2- energy surface and the neutr al Rb*-H-2 energy surfaces plays a very crucial role. A further comparison with two previous results reveals that the average vibrational disposal [f( v)] in MH changes dramatically as the excited alkali atom M* is varied from K* to Rb* and to Cs*. The [f(v)] value for the (K* + H-2) system is close to the prior distribution limit, but it becomes smaller and smaller for the (Rb* + H-2) system and for the (Cs* + H-2) system.