Conservation of the Kr+(2P1/2) state in the reactive quenching of Kr(5s′[1/2]) atoms by halogen-containing molecules

Abstract

The second metastable state of Kr, 5s′[1/2]0, was generated from the first metastable state, 5s[3/2]2, by optical pumping in a flow reactor. Under optimum conditions, the entire Kr(5s[3/2]2) concentration could be removed with more than 40% conversion to the Kr(5s′[1/2]0) state, which is stable in He carrier gas. The Kr(5s′[1/2]0) and Kr(5s[3/2]2) states have the Kr+(2P1/2) and Kr+(2P3/2) ion cores, respectively, as do the Kr+X−(D) and Kr+X−(B,C) states. The reactions of a series of fluorine-, chlorine-, and bromine-containing molecules, RX, with the Kr(5s′[1/2]0) and Kr(5s[3/2]2) atoms were studied by measuring the total quenching rate constants and by observing the KrX(B,C,D) product emission spectra. In contrast to the Kr(5s[3/2]2) atoms, which give KrX(B and C) products, the Kr(5s′[1/2]0) atoms have a high propensity to give KrX(D) plus a lesser amount of KrX(B), depending on the reagent, as products. Discrimination against KrX(C) formation by reactions of Kr(5s′[1/2]0) atoms is severe. The reactions with F2, NF3, and N2F4 exhibit the highest conservation of the Kr+(2P1/2) core, and these Kr(5s′[1/3]0) reactions give ≳70% KrF(D). The total quenching constants of Kr(5s′[1/2]0) atoms generally are equal to those for Kr(5s[3/2]2), but the branching fractions for KrX* formation from Kr(5s′[1/2]0) atoms generally are smaller than for Kr(5s[3/2]2) atoms. A correlation diagram based on conservation of Kr+ ion-core state and Ω=0− is developed to discuss these trends and the reactions of the Xe(6s′[1/2]0 and 6s[3/2]2) atoms. Due to the absence of KrX(C–A) emission from the Kr(5s′[1/2]0) atom reactions, the KrX(B–A) and Kr(D–A) transitions could be observed and the radiative branching ratios to the X and A states were assigned.