AUTODETACHMENT SPECTROSCOPY AND DYNAMICS OF VIBRATIONALLY EXCITED DIPOLE-BOUND STATES OF H2CCC-

Direct observation of the rotational fine structure levels of a vibrat ionally excited negative ion dipole-bound state (DBS) is reported. Aut odetachment resonances of H2CCC- were observed for the (2)A(1)-B-2(1) transition in one quanta of nu(6), nu(4), and nu(2) and two quanta of nu(6) vibrational modes of the DBS. Rotational assignments for both th e electronic ground state and the DBS were performed. Strong type (a) Coriolis coupling between nu(6) and vg in both the electronic ground a nd excited states was observed, and coupling constants were determined , QCISD ab initio calculations were performed for the ground state, th e negative ion, and the neutral state of H2CCC. The calculations on th e neutral agree well with measured vibrational frequencies of the dipo le-bound state. The autodetachment resonances contain information abou t the detachment dynamics via the observed linewidths, showing, e.g., that motions along the dipole moment axis significantly enhance autode tachment, indicating that the DBS is unstable with respect to neutral core motion which modulates the magnitude value of the dipole moment. (C) 1996 American Institute of Physics.