Stimulated emission pumping by two‐color resonant four‐wave mixing: rotational characterization of vibrationally excited HCO (X̃2A′)

Abstract

AbstractStimulated emission pumping by applying two‐color resonant four‐wave mixing was used to measure rotationally resolved spectra of the HCO (0,0,0) B̃2A′–(0, 3, 1)X̃2A′ transition. The formyl radical is produced by photodissociation of formaldehyde at 31710.8 cm−1 under thermalized conditions in a low‐pressure cell. In contrast to the highly congested one‐color spectrum of HCO at room temperature, the double‐resonance method yields well isolated transitions which are assigned unambiguously owing to intermediate level labeling. Eighty‐nine rotational transitions were assigned and yield accurate rotational constants for the vibrationally excited (0,3,1) band of the electronic ground state X̃2A′ of HCO. The determined rotational constant A = 25.84 ± 0.01 cm−1 is considerably higher than that for the vibrationless ground state and reflects the structural change due to excitation of the bending mode of the formyl radical. Copyright © 2003 John Wiley & Sons, Ltd.