High-resolution cavity ring-down spectroscopy has been used to record three vibronic bands of the ùA″–¹A′ (π*â†�n_O) transition of room-temperature formyl chloride (HClCO). These three bands (6₀¹, 5₀¹6₀¹ and 2₀¹5₀¹6₀¹) are all vibronically induced through the activity of the out-of-plane inversion vibration ν₆, and are found to obey type-a selection rules. Rotational constants have been derived from the analysis of these bands and used to give information on the geometrical structure of the excited state. The properties of the Ãstate are found to be intermediate between those of the corresponding states of formaldehyde and formyl fluoride.