Vibrationally resolved shape resonant photoionization of SiF4

We have measured vibrationally resolved fluorescence from SiF+4(D̃ 2A1) photoions to determine the vibrational branching ratio σ[v=(1,0,0,0)]/σ[v=(0,0,0,0)] in the excitation energy range 22<hν<70 eV. The branching ratio shows pronounced enhancements at hν=25 and 45 eV. The deviation from Franck–Condon behavior at higher energy (hν=45 eV) is attributed to a shape resonance and it appears that a shape resonance is also responsible for the lower energy feature (hν=25 eV). However, the present results in this lower energy region conflict with interpretations of previous vibrationally unresolved work. Applications of these results to general problems in polyatomic photoionization are discussed.