Electronic energy transfer from metastable argon atoms to krypton atoms

Abstract

The interaction between metastable argon atoms (3P2,0) and krypton atoms has been studied at room temperature using the flowing afterglow technique. Measurements of the emission intensities from the excited-krypton levels show that only Kr(5p[3/2]2) and Kr(5p[3/2]1) are primary products from Ar* (3P2). The pressure dependence of the emission intensities from other 5p krypton states shows that these are produced by collisional cascade from the 5p[3/2]2,1 levels; some rate constants for these cascade processes are reported. Absorption measurements using the 123.6 nm resonance transition of Kr demonstrate that the emitting Kr(5s 3P1) state carries no excess translational energy; therefore, it must be produced only via radiative cascade from Kr(5p) levels. Thus Ar (3P2) excitation rate constants of 5.6 and 0.65×10−12 cm3 molecule −1⋅sec−1 are established for excitation to Kr(5p[3/2]2) and Kr(5p[3/2]1), respectively. The Ar(3P2)+Kr reaction can serve as a reference for obtaining rate constants for excitation of other species via comparison of relative emission intensities and the technique is even useful in the vacuum ultraviolet if the appropriate branching ratio for the radiative cascade from 5p[3/2]2,1 to Kr(5s 3P1), established here as 0.301±0.006, is utilized. The emission from Kr* also can serve as a reference for determining absolute emission rates if [Ar(3P2)], [Kr], and the emission intensities are simultaneously measured. Quenching of Ar(3P0) by Kr gave an Ar–Kr* excimer emission, which peaks around 756.5 nm, emission from Kr(5p[1/2]0) at 758.7 nm, and formation of lower Kr(5p) states or deactivation to lower Ar(4s) states. Based upon the pressure dependence of these emission intensities, the excimer is formed by a fast three-body reaction with Ar* (3P0), and Kr(5p[1/2]0) is excited both by a slow two-body reaction with Ar(3P0) (∼3.4×10−15 cm3 molecule−1⋅ sec−1) and by bimolecular quenching of the excimer.