Large rotational energy release in collision-induced SiF C2Δ-B2Σ+ valence-Rydberg transfer

Distinct rotational population distributions were prepared in SiF C2Δ, ν = 0 radicals by laserexcitation. Collisions with H2 or N2 transferred a fraction of the C2Δ molecules to the lower-lying B2Σ+ state. B-X fluorescence spectra revealed the nascent rotational populations in the predominant B2Σ+, ν′ = 0 level. An unusually large fraction of the available energy is released as SiF rotation, supplementing the initial SiF rotational angular momentum. There is greater SiF B2Σ+ product rotation for N2 than for H2. A simple impulsive model is capable of rationalising these observations, consistent with previous vibrationally resolved measurements and the valence-Rydberg character of the transition.