CO(a 3Π), Its Production, Detection, Deactivation, and Radiative Lifetime

Abstract

This paper describes the first reported observation of the CO Cameron bands (a 3Π→X 1Σ+) produced from CO through photon absorption processes. The technique depends on quasiresonance fluorescence processes involving d 3Δ↔X 1Σ+ and a′ 3Σ+↔X 1Σ+ transitions and subsequent radiation from these triplet levels to the a 3Π state. From experiments in which the exciting lamp is pulsed, time decay measurements permit evaluation of the quenching rate constants for CO(a 3Π) by CO, NO, O2, H2, and CO2. The radiative lifetime of CO(a 3Π) has been obtained by use of the quenching rate constants, the intensities of the a 3Π populating transitions, and the Cameron band intensities, and it has an average value of 4.4±1.1 msec. Transfer of electronic energy takes place from CO(a 3Π) to NO, resulting in production of two radiating states, NO(A 2Σ) and NO (B 2Π), with approximate efficiencies of 23% and 10%, respectively. Either of these may be used as a monitor of the CO(a 3Π) state. Quenching of CO(a 3Π) by N2 leads to production of N2(A 3Σu+), but rate constants will have to be evaluated as a function of the degree of CO(a 3Π) vibrational excitation.