Collisional efficiencies for vibrational energy relaxation of C6F14 and C8F18: Dependence on deactivator mass

Abstract

Rate coefficients, kVT, for the deactivation of vibrationally excited C6F14 and C8F18 with average excitation energies ranging from 5000 to 30 000 cm−1 were measured via time resolved optoacoustics for a series of 13 deactivators. Relative collision efficiencies (β=kVT/kHS=〈〈ΔE〉〉/〈E〉), an intrinsic measure of the deactivator, were calculated. The average energy removed per collision, 〈〈ΔE〉〉, was linear with 〈E〉 since β was found to be independent of energy for all deactivator-substrate combinations. The trends for the deactivators with the 6 and 8 carbon atom substrates were similar except that β was ∼15% smaller for the larger substrate. The efficiency for the rare gases increases from helium to neon to argon and then decreases to krypton followed by a slight leveling off for xenon. This trend with deactivator mass was also observed for the polyatomic deactivators studied. The rapid rise and slow fall in β vs mass can be simulated by an encounter between the deactivator and a diatomic substrate containing a pseudo atom with a mass of ∼30 amu.