Theoretical investigation of the relaxation of the bending mode of CH2(X) by collisions with helium.

We have earlier determined the dependence on the bending angle of the interaction of the methylene radical (CH2) in its X3B1 state with He [L. Ma, P. J. Dagdigian, and M. H. Alexander, J. Chem. Phys. 136, 224306 (2012)]. By integration over products of the bending vibrational wave function, in a quantum close-coupled treatment we have calculated cross sections for the ro-vibrational relaxation of CH2(X). Specifically, we find that cross sections for a loss of one vibrational quantum (vb = 21 and 10) are roughly two orders of magnitude smaller, and those for a loss of two vibrational quanta (vb = 20) four orders of magnitude smaller, than those for pure rotational relaxation. In addition, no clear cut dependence on the energy gap is seen. [ABSTRACT FROM AUTHOR]