Electronic-to-vibrational energy transfer efficiency in the O(1D)–N2 and O(1D)–CO systems

Abstract

With the aid of a molecular resonance fluorescence technique, which utilizes optical pumping from the v=1 level of the ground state of CO by A1Π-X1Σ+ radiation, we have investigated the efficiency of E-V transfer from O(1D) to CO. O(1D) is generated at a known rate by O2 photodissociation at 1470 Å in an intermittent mode, and the small modulation of the fluorescent signal associated with CO(v=1) above the normal thermal background is interpreted in terms of the E-V transfer efficiency. The CO(v=1) lifetime in this system is determined mainly by resonance trapping of their fundamental band, and is found to be up to ten times longer than the natural radiative lifetime. For CO, (40 ± 8)% of the O(1D) energy is converted into vibrational energy. By observing the effect of N2 on the CO(v=1) fluorescent intensity and lifetime, it is possible to obtain the E-V transfer efficiency for the system O(1D)–N2 relative to that for O(1D)–CO. The results indicate that the efficiency for N2 is (83 ± 10)% of that for CO. In both cases the initial vibrational distribution remains unspecified. The relatively high efficiency of the O(1D)–N2 reaction implies that it is the sole source of the N2 vibrational temperature in the earth's upper atmosphere.