Pl. James et al., RATE COEFFICIENTS FOR THE VIBRATIONAL SELF-RELAXATION OF NO(X-2-PI, V=3) AT TEMPERATURES DOWN TO 7 K, Chemical physics letters, 276(5-6), 1997, pp. 423-429
Infrared-ultraviolet double resonance (IRUVDR) experiments have been i
mplemented in the super-cold environment provided by a CRESU (Cinetiqu
e de Reaction en Ecoulement Supersonique Uniforme) apparatus. This met
hod has enabled us to measure rate coefficients for the vibrational se
lf-relaxation of NO(X (2) Pi; upsilon = 3), i.e. NO(upsilon = 3) + NO
--> NO(upsilon < 3) + NO. Using different Laval nozzles, results have
been obtained at six different temperatures between 85 and 7 K. The ra
te coefficients increase strongly as the temperature is lowered. The e
ndothermicity of single quantum vibrational-vibrational (V-V) energy e
xchange (Delta E/hc = 55.9 cm(-1)) means that the rate of this process
must decrease markedly at the lowest temperatures of our experiments.
Therefore, the high relaxation rates which are observed must be due t
o vibrational-translational (V-T) energy transfer. It is proposed that
this process is efficient because of the transient formation of(NO)(2
) collision complexes in which intramolecular vibrational energy trans
fer occurs at rates competitive with re-dissociation of the dimer to N
O(upsilon = 3) and NO(upsilon = 0). (C) 1997 Elsevier Science B.V.