Experimental and theoretical study of intramultiplet transitions in collisions of C([sup 3]P) and Si([sup 3]P) with He.

We present a combined theoretical and experimental study of intramultiplet transitions in collisions of C([SUP3]P) and Si([SUP3]P) with He. Relaxation rate constants have been measured using the CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme) technique at 15 K for C([SUP3]P) + He and over the 15-49 K temperature range for Si([SUP3]P) + He. Three sets of interaction potentials have been generated for the [SUP3]Σ[SUP-] and [SUP3]∏ electronic states of CHe and SiHe systems. Quantum-mechanical calculations have been performed on these potential curves for the spin-orbit relaxation and excitation. Cross sections and rate constants are very sensitive to the interaction potential. For the Si([SUP3]P) + He system, an overall good agreement between the theoretical and experimental rate constants is found with the best quality interaction potential, while for the C([SUP3]P) + He system experimental rate constants are much smaller than the theoretical ones. [ABSTRACT FROM AUTHOR]