+ Vibrational energy transfer between I2„B 3⌸0u , ␯Ј = 21… and He at very low temperatures: Impulsive versus complex formation mechanisms assisted by tunneling through the centrifugal barrier

IVÁN CABANILLAS-VIDOSA; CARLOS A. RINALDI; PINO, GUSTAVO; J.C.FERRERO

JOURNAL OF CHEMICAL PHYSICS

AMER INST PHYSICS

Año: 2008 vol. 129 p. 303 - 312

0021-9606

21−⌬The temperature dependence of the state-to-state vibrational relaxation rate constant ͑k␯ ␯͒ for collisions between I2͑B , ␯Ј = 21͒ and He at very low kinetic energies was studied. The fluorescence from I2͑B , ␯Ј = 21− ⌬␯Ј͒ with ⌬␯Ј = 1 – 5 indicates that in the temperature range of 0.6– 8.2 K these 21−⌬ states are populated by only one collision with He. The behavior of k␯ ␯ with temperature can be divided into two groups. The group with quantum changes ⌬␯Ј = 1 – 3 shows scattering resonancesin the low temperature region, with a general monotonical decrease of the rate constant with temperature, suggesting the importance of van der Waals interactions. This behavior is supported bythe calculation of the probability of tunneling through the centrifugal barriers. For collisions in which 4–5 quanta are lost in a single event, there are no evidences of scattering resonances and thevalues of the relaxation rate constants could be determined only at the highest temperatures of this study. This suggests that relaxation occurs via impulsive collisions. The branching ratios for eachchannel are also temperature dependent and this behavior also suggests that the energy transfer mechanism changes with ⌬␯Ј