Observation of the predfssociated,quasilinear B(~1A') state of CHF by optical-optical double resonance

摘要

We report the first observation of the predissociative B state of a halocarbene molecule.Rovibronic energy levels were measured in the B(~1A') state of CHF by fluorescence dip detected optical-optical double resonance spectroscopy via the A state.The origin was found to lie 30 817.4 cm~(-1) above the zero point level of the X state.Rotational transitions within six purely bending states,and states involving one or two quanta of CF-stretch were observed,including the vibrational angular momentum components.Interpretation of the spectrum,with support of ab initio calculations,shows that CHF is quasilinear in the B state with a small (-200 cm-1) barrier to linearity which lies below the zero-point level.The rotational constant,B=1.Q4 to 1.09 cm-1,depending on vibrational state,again in good agreement with theory.All observed B state levels were predissociative,as evidenced by Lorentzian line broadening.Linewidths varied with initial state from 0.7-10.8 cm-1,corresponding to excited state lifetimes of 0.5-8 ps.