Rotational structure in the (A)over-tilde(1)A ''-(X)over-tilde(1)A ' spectrum of formyl chloride

High-resolution cavity ring-down spectroscopy has been used to record three vibronic bands of the (A) over tilde(1)A"(1)-(X) over tilde(1)A' (pi*<--n( O)) transition of room-temperature formyl chloride (HClCO). These three ban ds (6(0)(1), 5(0)(1)6(0)(1) and 2(0)(1)5(0)(1)6(0)(1)) are all vibronically induced through the activity of the out-of-plane inversion vibration nu(6) , and are found to obey type-a selection rules. Rotational constants have b een derived from the analysis of these bands and used to give information o n the geometrical structure of the excited state. The properties of the (A) over tilde are found to be intermediate between those of the corresponding states of formaldehyde and formyl fluoride.