Double-resonance spectroscopy of the high Rydberg states of HCO. III. Multiple pathways in the vibrational autoionization of the bending overtone

Ultraviolet first-photon absorption selects individual rotational levels in the Renner–Teller split (020) vibronic band system in the 3pπ 2Π Rydberg state of HCO. These gateway states serve as originating levels for vertical second-photon transitions to vibrationally autoionizing Rydberg series converging to individual rotational levels associated with the (0200) and (0220) states of HCO+. Linewidths of assigned series convey information on autoionization dynamics. Resonances throughout the (020) autoionization spectrum match sharp profiles seen earlier for series converging to HCO+(010). Linewidths for autoionization via relaxation both of the bending fundamental and its overtone are measurably narrower than resonances built on CO stretch, (001), which indicates that mode-selectivity inhibiting bending autoionization relative to stretch extends to the bending overtone. Features in the (020) spectrum that fall below the threshold energy for decay by autoionization to the (010) continuum appear with dimini...