Collisional quenching and energy transfer of NO (D 2Σ +, v′ = 0)

Abstract

We report, in this paper, the rate constants for electronic quenching of NO (D 2Σ +, v′ = 0) by gases He, Ar, Xe, NO, N 2, O 2, CO 2, N 2O, CF 4, and SF 6. The experiments were carried out by exciting the (0, 0) band of the D 2Σ +–X 2Π transition at 187.5 nm, and detecting the (0, 2) band fluorescence at 206 nm under various pressures of quenching gases. Based on the derived half quenching pressures and the known radiative lifetime of the excited state, the quenching rate constants were determined. Rate constants are all near gas kinetic and are in the following order: SF 6 > CO 2 > N 2O > O 2 > NO > N 2 > Xe > CF 4 > He > Ar. Our rate constants are comparable with the existing literature data. For N 2, the resonant energy transfer between NO (D) and N 2 was investigated. We observed quenching and enhanced fluorescence processes caused by the energy transfer between the excited states. Such pressure dependent processes could cause the disagreement among previous investigators. We also employed the collision complex model to derive the potential well depths of the van der Waals (vdw) complexes. Calculations were made by involving empirical kinetic data for the quenching gases as well as the experimental quenching cross-sections. Results show deep vdw potential wells for NO (D) with the gases studied here. Among all data, the potential well depths for noble gases are smaller compared with other reactive gases. The calculated results are then compared with the experimental well depths of NO(D)Ar.