Abstract
Dispersed fluorescence spectra of B̃ 2 A' -X̃ 2 A' transitions are measured on exciting HCO to the vibrational levels (0,0,0), (0,0,1), (0,1,0) and (1,0,0) of B̃ 2 A' in a gas cell. Vibrational energies of bound and resonant states are determined for energy up to 17 500 cm -1 from the ground vibrational level of the X̃ 2 A' state. Rotationally resolved spectra of the bands B̃ 2 A' -X̃ 2 A' 2 3 0 3 1 0 , 2 4 1 and 2 2 0 3 2 1 were recorded and analyzed. Abnormal intensities in the P, Q and R branches are due to the mechanism of "axis switching". From the ratios of emission intensity of a- and b-type transitions, without taking into account the varied lifetimes of rotational states of the upper electronic state, the directions of transition dipole moments of these bands are determined to be 39 - 43° to the inertial a axis.