The relaxation of HCN(101) by V-T,R and V-V energy transfer

• Published in: Chemical physics 1984-09, Vol.89 (1), p.141-150
• Main Authors: Cannon, B.D., Francisco, J.S., Smith, I.W.M.
• Format: Article
• Language: English
• Subjects: Atomic and molecular collision processes and interactions; Atomic and molecular physics; Exact sciences and technology; Physics; Scattering of atoms, molecules and ions
• ISSN: 0301-0104
• DOI: 10.1016/0301-0104(84)85304-5

Tuned output from an optical parametric oscillator has been used to excite HCN directly to its (101) level. Using a cold gas filter to distinguish between the time-resolved fluorescence from HCN(101) and that from HCN(001), rate constants for relaxation from both levels have been obtained for a number of collision partners: (i) He, Ne, Ar, Kr and Xe, and (ii) HCN, N 2, O 2, CO, H 2, D 2, CO 2, N 2O, OCS, C 2H 2 and CH 4. HCN(101) is relaxed about five times faster than HCN(001) by the rare gases, the rate constants (cm 3 molecule −1 s −1) at 298±4 K being: k 101 He = (3.9±0.35)×10 −14, k 101 Ne = (3.2±0.2)×10 −14, k 101 Ar = (2.6 5±0.18)×10 −14, k 101 Kr = (2.4 5±0.25)×10 −14 and k 101 Xe = (3.0 5±0.25)×10 −14. The similarity of the relaxation rates with different noble gases indicates that the major process is a near-resonant transfer of HCN, presumably to the (03 11) level. With the molecular collision partners, it is more difficult to assign a predominant mechanism, except in the case of CO and OCS, where it appears that near-resonant intermolecular vibrational-vibrational (V-V) energy transfer of the ν 1 quantum is important.