Collision energy dependence of the cross sections for the electronic excitation transfer reactions: Rg(3P0,2)+N2(X 1Σg)→Rg(1S) +N2(C 3Πu) (Rg=Ar, Kr)

Abstract

The collision energy dependence of the integral cross sections for the title reactions were determined using crossed molecular beams and time-of-flight energy selection techniques. Applying arc-heated rare gas atom beams, the relative collision energies of metastable Ar(3P0,2) and Kr(3P0,2) atoms were selected between 0.4 and 2.5 eV for Ar(3P0,2)+N2, and 0.6 and 1.7 eV for Kr(3P0,2)+N2 systems. The negative energy dependence of the cross sections for the prototype reaction Ar(3P0,2)+N2 agrees well with the results of Parr and Martin in the overlapped energy range (0.4–0.8 eV). The absolute cross sections were determined by normalizing our cross sections to the ones of Parr and Martin. As to the endoergic Kr(3P0,2)+N2 reaction, the product fluorescence from N2(C 3Πu–B 3Πg) was also observed. The total cross section for this reaction exhibits a steep increase near the threshold for each component state [ΔH(3P0)=0.47 and ΔH(3P2)=1.12 eV] and then tends to level off. Assuming the component ratio Kr(3P2)/Kr(3P0) to be statistical in the arc-heated beams, the cross section for each reaction was evaluated by convolution analysis. The post-threshold cross sections for these processes are one to two orders of magnitude smaller than those obtained for Ar(3P0,2)+N2 reaction. The higher reactivity found for Kr(3P2) than for Kr(3P0) is consistent with the quenching rates of Ar(3P0) and Ar(3P2) by N2 obtained by Piper, Velazco, and Setser [J. Chem. Phys. 59, 3323 (1973)]. The present findings suggest that the same type of interaction is also effective for these collision-induced nonadiabatic Kr(3P0,2)+N2 processes as the one, such as spin-orbit interaction, which is applicable between Ar(3P0,2) and N2.