Experimental Study On Collisional Energy Transfer In Pure Rubidium And Rb-H₂ System

(1) The quantum state population distributions of the RbH product resulting from the reaction Rb(62D)with H2 are determined using a laser pump-probe technique in a crossed heat-pipe oven. For the investigated reaction,the nascent RbH product molecules were found to populate the lowest two vibrational (v=0,1) levels of the ground electronic state but could not be detected in any higher vibrational state. Rotational distributions of RbH products obtained for v=0 and 1 state appear to be monomodal,peaking in J=8-10. A plot of logarithm of relative population of states J divided by the degeneracy factor (2J+1) against J(J+1) was yielded. The linearity of the plot establishes the Boltzmann form for rotational distribtions. The nascent RbH rotational temperatures are found to be slightly below the cell temperature.In contrast,the hot vibrational temperatures are observed.The relative vibrational population are determined to be 0.65 for v″=0 and 0.45 for v″=1. The avera ge vibrational and rotational energy release can be computed. The relative fractions , and of average energy disposal are derived as 0.038,0.132 and 0.830,having a major translation energy release. All of the above result support the assumption that the Rb-H2 reactive collision occurs primarily in a collinear geometry and not an insertion. By comparing the spectal intensities of the RbH action spectra,the relative reactivity with H2 for the three studied atoms is in an order of Rb(72S)> Rb(52D)>Rb(62D).(2) At different Rb densities,Rb vapor was irradiated in a glass fluorescence cell with pulses of radiation from a pumped-laser, populating Rb2(B1∏u)state by single-photon absorption. Energy transfer in Rb2(B1∏u)+Rb(5S) collision is studied using methods of atomic and molecular fluorescence. The decay signal of time-resolved fluorescence from B1∏u→X1∑g+ transition was monitored.The effective lifetimes of the B1∏u state can be resolved. The plot of reciprocal of effective lifetimes of the B1∏u state against Rb densities yielded the slope that indicated the total cross section for deactivation and the intercept that provided the radiative lifetime of the state. The radiative lifetime 23.5ns for the B1∏u is obtained. The cross section for deactivation of the Rb2(B1∏u) molecules by collisions with Rb atoms isσ3=(4.33±0.14)×10-15cm2. At the different Rb densities, the time-integrated intensities of the resulting Rb emission lines I(5 P 3/2→>5 S 1/2) and I(5 P 1/2→5 S 1/2) were measured. The absolute values for Rb2(B1∏u)+Rb-Rb2(X1∏g+)+Rb(5 PJ) collisional transfer cross sections have been obtained. The cross sections areσ31=(2.86±0.13)×10-16cm2 (for transferring to 5 P1/2)andσ32=(8.30±0.38)×10-16cm2 (for transferring to 5 P3/2),respectively.