Abstract
Fluorescence spectra of the B̃ 2 A′-X̃ 2 A′(0,0) band of thermalized HCO at 298 K were recorded. The lifetimes of nascent HCO B̃ 2 A′(0,0,0) states produced from acetaldehyde photolyzed at a wavelength of 310.9 nm in a supersonic jet were obtained for rotational states to N=26, 24, and 18 for K a =0, 1, and 2, respectively. The lifetimes of these states decrease as the K a and N quantum numbers increase; they vary in the ranges 24-89 ns for K a =0 states, 12-52 ns for K a =1 states and 14-18 ns for K a =2 states. An a-type Coriolis interaction between the B̃ 2 A′ and à 2 A″ states is proposed to account for predissociation of the low vibrational levels of B̃ 2 A′. The spectral intensity shows anomalous behavior in that the intensity ratio of transitions Q R 0 / Q P 0 is nearly 2; similar phenomena are observed for other branches. The mechanism of axis switching in the B̃ 2 A′-X̃ 2 A′ transition is because the geometry is altered during the excitation; consequently the principal inertial axes are rotated to account for the intensity anomaly. Corrections for the lifetime variation and intensity anomaly are necessary_to obtain accurate relative populations of the X̃ 2 A′ state from fluorescence spectra B̃ 2 A′-X̃ 2 A′. © 1996 American Institute of Physics.