Collision energy dependence of the cross sections for the dissociative excitation reactions: Rg(3P0,2) +NH3→Rg+NH(A 3Π, c 1Π)+H2 (Rg=Ar, Kr)

Abstract

The integral cross sections for the title reactions were determined for the relative collision energies between 0.3 and 1.4 eV by applying arc-heating metastable rare gas beams to a crossed molecular beam–time-of-flight (TOF) energy selection technique, in which product fluorescence intensities from both NH(A 3Π–X 3Σ−) and NH(c 1Π–a 1Δ) bands were monitored. With Ar(3P0,2 ) excitation, the relative branching fractions of nascent NH(A 3Π) and NH(c 1Π) formation were found to be invariant with the collision energy within the experimental error. With Kr(3P0,2) excitation, however, no apparent NH(c 1Π–a 1Δ) emission was observed, only emission from NH(A 3Π) was observed. The absolute cross section for formation of these nascent NH radicals was also determined. Collision energy dependence of the cross section for the reaction Ar (3P0,2) +NH3→Ar(1S0)+NH(A 3Π,c 1Π)+H2 was found to be negative, whereas that for the reaction Kr(3P0,2 )+NH3→Kr(1S0)+NH(A 3Π)+H2 showed positive dependence in the collision energy range studied. Possible mechanisms for the formation of NH(A 3Π,c 1Π) from Rg(3P0,2)+NH3 are discussed.