Hot Band Spectroscopy of the Formyl Cation, H¹²C¹⁶O⁺

Midinfrared spectra of the formyl cation, HCO+, were recorded by direct absorption in a glow discharge (composition CO, 50 mTorr; H2, 50 mTorr; He, 7 Torr) using a color center laser spectrometer and velocity modulation with heterodyne detection. The bands measured were 1000–0000, 1110–0110, 1200–0200, 1220–0220, 1001–0001, 1111–0111, 2000–1000, and 1002–0002. These bands were analyzed and fitted together with all other available rotationally resolved spectra to arrive at a new set of spectroscopic constants for HCO+. The relative intensities were fit to obtain a rotational temperature, Trot = 434 ± 7 K, and vibrational temperatures for each mode, T1 = 3300 ± 240 K, T2 = 841 ± 15 K, and T3 = 3157 ± 68 K.