Vibrational relaxation of HCN(001) by the noble gases, O2, N2 and CO

Abstract

The tuned output from an optical parameteric oscillator has been used to excite HCN to its (00⁰1) level for measurements of vibrational energy transfer. By observing time-resolved infrared fluorescence from the (00⁰1) level in the presence of different collision partners, the following rate constants (k/cm³ molecule^–1 s^–1) were obtained at 297 ± 4 K: k_He=(6.4 ± 0.4)×10^–15; k_Ne=(6.3 ± 0.6)×10^–15; k_Ar=(6.5 ± 0.5)×10^–15; k_Kr=(7.1 ± 0.7)×10^–15; k_O2=(1.34 ± 0.05)×10^–14; k_N2=(2.2 ± 0.2)×10^–14; k_CO=(3.3 ± 0.2)×10^–14.

It is argued that, in all cases, relaxation from the (00⁰1) level is rate-determining and that the dominant process is probably transfer into neighbouring levels, such as (12⁰0), associated with the ν₁ and ν₂ modes.