Double-resonance spectroscopy of the high Rydberg states of HCO. IV. Vibrational autoionization dynamics as a function of bending amplitude

Double-resonant ionization-detected absorption experiments extend an invest igation of the autoionization dynamics of HCO to include the second overton e of the bend. In these experiments, first-photon transitions to the 3p pi (2)Pi Rydberg state select single rovibrational levels for second-photon sc ans of vibrationally autoionizing high Rydberg series that converge to spec ific rovibrational limits of HCO+. Line shapes reflect coupling widths that join discrete states built on vibrationally excited cores with underlying, vibrationally relaxed continua. Scans of series converging to HCO+ with on e and two quanta of bend show narrow linewidths, reflecting relatively long autoionization lifetimes. However, for cores excited to the second harmoni c of the bend, certain series abruptly broaden, indicating ultrafast decay. The implications of these results are discussed in terms of a qualitative extension of multichannel quantum defect theory to triatomic molecules. (C) 2000 American Institute of Physics. [S0021-9606(00)01004-7].