Vibrational excitation of carbon monoxide following quenching of the a3Π state

Abstract

Vibrationally excited CO, produced from the flash photo-excitation of carbon monoxide, has been observed in the ν″= 1 progression of the fourth positive system (A¹Π–X¹Σ⁺) in the vacuum ultra-violet. Experiments with the appropriate optical filters indicate that the observed vibrational energy results from electronic energy transfer from CO(a³Π), directly excited by absorption of light from the photoflash in the far ultra-violet via the Cameron bands (a³Π–X¹Σ⁺). The efficiency of conversion of this electronic energy to vibration in ν″= 1 is estimated to be about 20%. Vibrational excitation of CO by infra-red absorption is unimportant in this system. No products of photolysis could be detected either spectroscopically or by their effect on the relaxation of CO(ν″= 1). The decay of CO(ν″= 1) was monitored in the presence of Ar, H₂, N₂ and O₂ and the number of collisions for deactivation measured. These were 1.6 × 10⁶, 4.9 × 10⁵, 5.1 × 10⁴ and ∼10⁸ for H₂, N₂, O₂ and CO itself, respectively. Relaxation in CO is controlled almost entirely by spontaneous emission. The decay of CO(ν″= 1) is discussed in terms of the theories for vibration-translation relaxation and vibrational exchange.