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.