Resonance enhanced multiphoton ionisation of the SiF radical: a reinvestigation

We report multiphoton ionisation spectra of ground (X2Π) state SiF radicals, resonance enhanced at the two-photon energy by the v′ = 1 level of the C″2Σ+ excited state, at much higher resolution than hitherto. An earlier suggestion by Dulcey and Hudgens that the anomalous intensity of the C″-X (1,0) two-photon transition might be attributable to additional, accidental, resonance enhancement at the one-photon energy by levels of the A2Σ+, ν′ = 0 state is confirmed, and the double resonance enhancement analysed in detail. A similar accidental double resonance enhancement, involving levels of the A2Σ+, ν′ = 1 state at the one-photon energy, is proposed to explain the observed fragmentary pattern of lines associated with the C′2Π-X (5,0) two-photon transition.