High-resolution ro-vibrational and rotational spectroscopy of HC 3 O .

The ro-vibrational and pure rotational spectra of the linear ion HC 3 O + have been investigated in a 4 K cryogenic ion trap instrument. For this, a novel action spectroscopic technique, called leak-out-spectroscopy (LOS, Schmid et al. , J. Phys. Chem. A 2022, 126 , 8111), has been utilized and characterized. In total, 45 ro-vibrational transitions within the fundamental band of the ν 1 C-H stretching mode were measured with a band center at 3237.132 cm -1 , as well as 34 lines from the combination band ν 2 + ν 4 , and 41 lines tentatively identified as the combination band ν 2 + ν 5 + ν 7 , interleaved and resonant with ν 1 . Surprisingly, also two hot bands were detected despite the cryogenic operation temperature. Based on the novel action spectroscopy approach, a new double-resonance rotational measurement scheme was established, consisting of rotational excitation followed by vibrational excitation. Seven rotational transitions were observed between 89 and 180 GHz. Highly accurate spectroscopic parameters were extracted from a fit using all available data. In addition, a pulsed laser system has been employed to record a low resolution vibrational spectrum, in order to demonstrate the compatibility of such lasers with the LOS method.