LIFETIMES OF VIBRATIONAL LEVELS IN THE (B)OVER-TILDE(2)A' STATE OF HCO

We measure the fluorescence decays for low-lying rotational states in the first eight vibrational levels of HCO (B) over tilde(2)A'. Some lo ng-lived decays exhibit weak quantum beats that we attribute to a high er-order hyperfine perturbation in the B state. We estimate fluorescen ce quantum yields by combining measured fluorescence intensities and a calculated electronic transition moment. The estimated nonradiative d ecay rates increase with increasing vibrational excitation and exhibit mode specificity. We discuss possible vibronic coupling mechanisms, i ncluding spin-orbit coupling to quartet states and predissociation via the (A) over tilde(2) Pi((2)A '') and (X) over tilde(2)A' states.