Vibrational relaxation of HCN by 3He, 4He, H2, HD, D2, CH4 and C2H6

Abstract

The tuned output from an optical parametric oscillator has been used to excite HCN to its (011) and (101) levels for measurements of collisionally induced vibrational energy transfer. Using an HCN ‘cold-gas filter’ to distinguish between the time-resolved infrared fluorescence from the initially prepared state and that from HCN(001), rate constants have been measured at 297 ± 4 K for the removal of HCN molecules from the levels (011), (101) and (001) in collisions with ³He, ⁴He, H₂, HD, D₂, CH₄ and C₂H₆. The results are discussed in relation to: (a) the likely mechanisms for relaxation in these systems and (b) the possibilities of operating HCN vibrational transition lasers pumped either by exothermic reactions of CN radicals in which a hydrogen atom is transferred and vibrationally excited HCN produced or by vibrational-to-vibrational energy transfer from H₂.