Dipole moments of highly vibrationally excited HCN: Theoretical predictionof an experimental diagnostic for delocalized states

Vibrational state specific dipole moments are diagnostic of the degree of l ocalization of vibrational states in highly vibrationally excited HCN. Usin g a newly calculated global ab initio dipole moment function and previously calculated highly accurate vibrational wave functions, we show that deloca lized (i.e., isomerizing) vibrational states of HCN possess markedly lower dipole moments than localized HCN or HNC states. We also show that the vibr ational quantum number dependence of the dipole moment can be used to disti nguish delocalized states from localized Franck-Condon-dark states that are made observable by perturbations with localized Franck-Condon-bright state s. Furthermore, using classical trajectory analysis we introduce and descri be a new experimental approach to obtain these data, which relies on combin ing optical pumping and state specific molecular transport with hexapoles. With this method it is possible to determine state specific dipole moments with high accuracy and precision. (C) 2001 American Institute of Physics.