POLARIZATION EFFECTS IN ELECTRONICALLY INELASTIC-COLLISIONS - SIFC2-DELTA-2-]SIFB2-SIGMA(+)+H-2(H)

Linearly polarised laser excitation was used to prepare aligned, elect ronically excited samples of SiF molecules. Selected, spectroscopicall y isolated bandheads in the B-X and C-X systems were excited, and appr opriate bands resolved in the dispersed fluorescence. The observed deg ree of polarisation anisotropy, R, of B-X(3,2) fluorescence from the d irectly excited SiFB(2)Sigma(+), v = 3 state agreed, within experiment al error, with the theoretical prediction. The value of R for C-X(0,0) fluorescence from the SiFC(2)Delta, v = 0 level excited in the presen ce of H-2 land Ar carrier) was reduced from the theoretical prediction , consistent with previous observations of partial rotational redistri bution under these conditions. As also previously established, collisi ons with H-2 induce SiFC --> B transfer. The SiFB(2)Sigma(+), v' = 0 p roduct was found to be significantly less polarised than the SiFC(2)De lta, v = 0 population from which it was produced. Two simple classical models were developed for the degree of depolarisation based on alter native assumptions about the spatial distribution of the additional an gular momentum, Delta J, imparted during the collision process, relati ve to the initial J. Both predict a degree of depolarisation consisten t with the experimental observations in this case. We note that there exists in principle an impulsive dynamical limit in which the product state will remain partially aligned regardless of the relative magnitu des of J and Delta J. (C) 1998 Elsevier Science B.V. All rights reserv ed.