Chemical Applications of Metastable Argon Atoms. IV. Excitation and Relaxation of Triplet States of N2

Abstract

An argon flow system containing about 0.01% of metastable argon atoms (3P2,0) in the absence of other energy carriers is described and characterized. The interaction of these metastable atoms with nitrogen gives radiative transitions of N2 from C(3Πu) → B(3Πg) → A(3Σu+) and finally A(3Σu+) → X(1Σg+). Absolute-intensity measurements, high-resolution spectra, and pressure-dependence data show that independent channels exist for production of C(3Πu) and B(3Πg). Unusual nonequilibrium populations of the rotational levels, the three spin sublevels, and the λ-doublet levels were found for the N2(C3Πu) state. Possible mechanisms responsible for producing these populations are discussed. Study of the dependence of these populations upon pressure permitted evaluation of collisional relaxation within the various levels of N2(C3Πu). It was shown that rotational relaxation mainly occurs by ΔK = ± 1 with a rate constant of 7.4 × 1013 cm3 mol−1·sec−1. The rate constant for electronic quenching of N2(C3Πu) by argon is less than 2 × 1011 cm3 mol−1·sec−1. Relaxation among the three spin sublevels was found to be slower than rotational relaxation.