Vibrational energy transfer between I2(B3ƒÀ+ou, v¡¦=21) and He at very low temperatures: impulsive vs complex formation mechanisms assisted by tunneling through the centrifugal barrier

I. CABANILLAS VIDOSA; C. A. RINALDI; G. A. PINO; J. C. FERRERO

JOURNAL OF CHEMICAL PHYSICS

American Institute of Physics

Año: 2008 vol. 129 p. 144303 - 144309

0021-9606

The temperature dependence of the state-to-state vibrational relaxation rate constant  (k21 - dv´) for collisions between I2(B, v´ = 21) and He at very low kinetic energies was studied. The fluorescence from I2(B, v´ = 21 - dv´) with dv´ = 1 - 5 indicates that in the temperature range of 0.6 - 8.2 K these states are populated by only one collision with He. The behavior of k21 - dv´ with temperature can be divided into two groups. The group with quantum changes dv´ = 1 - 3 shows scattering resonances in 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 by the 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 the values 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 each channel are also temperature dependent and this behavior also suggests that the energy transfer mechanism changes with dv´.