Radiative Lifetime and Quenching Rate Constants of PF(b1.SIGMA.+) and Tests for an Electronic to Vibrational Energy Transfer Quenching Mechanism

Abstract

A dc discharge in a dilute flow of PF[sub 3] in He was used as a source of PF(b[sup 1][Sigma][sup +]) molecules in a flow reactor to measure the radiative lifetime and quenching rate constants for 38 reagent molecules at 300 K. The concentration of PF(b[sup 1][Sigma][sup +]) in the reactor was about 2 x 10[sup 8] molecule cm[sup [minus]3]. The decay rate of the PF(b[sup 1][Sigma][sup +]) concentration was monitored from the intensity of the PF(b-X) transition, and the radiative lifetime was measured to be 9.7 [+-] 1.2 ms. The quenching rate constants are small, except for O[sub 2] and Cl[sub 2], and in the range 10[sup [minus]12]-10[sup [minus]14] cm[sup 3] molecule[sup [minus]1] s[sup [minus]1]. The dependence of the other rate constants on properties of the reagent is consistent with an electronic-to-vibrational (E-V) quenching mechanism, and this was confirmed by studying several isotopic pairs of molecules, such as H[sub 2]/D[sub 2], H[sub 2]O/D[sub 2]O, and CH[sub 3]CN/CD[sub 3]CN. The quenching rate constants are compared to predictions of a model for E-V energy transfer. The reaction with O[sub 2] proceeds by electronic energy transfer to give O[sub 2](b[sup 1][Sigma][sup +]). 39 refs., 9 figs., 3 tabs.