EXCITED ELECTRONIC STATES OF THE SIF2 RADICAL STUDIED BY RESONANCE-ENHANCED MULTIPHOTON IONIZATION SPECTROSCOPY AND AB-INITIO METHODS

SiF2 radicals have been produced by the gas-phase reaction of SiH4 wit h F atoms in a flow reactor and detected by mass-resolved resonance en hanced multiphoton ionisation (REMPI) spectroscopy. Two band systems a re observed. One, a series of one-photon resonances in the wavelength range 210-230 nm, we associate with the previously documented <(A)over tilde B-1(1)><--<(X)over tilde (1)A(1)> transition. The observed long progression in the excited state bending mode, nu(2), reflects the in crease in equilibrium bond angle that accompanies this electronic tran sition. We also identify three:two-photon resonances in the wavelength range 315-325 nm. Two we can definitely associate with the <(B)over t ilde B-1(2)><--<(X)over tilde (1)A(1)> transition. Polarisation studie s show the third resonance: to involve an excited state of (1)A(1) sym metry. Guided by the results of companion ab initio calculations we pr esent evidence for and against assignment of this feature as the (vibr onically induced) (B) over tilde<--<(X)over tilde 3(0)(1)> band, or as a hitherto unidentified (1)A(1)<--<(X)over tilde (1)A(1) electronic o rigin. The calculations also enable prediction of the term values of a further eight, as yet unobserved, excited slates of SIF2.