The Rotational Spectrum of trans-HOCO and DOCO

Part of the rotational spectrum of the hydroxyformyl radical, HOCO, and its deuterated analog has been detected at frequencies between 230 and 300 GHz. The radical was formed in a flow system by the reaction between chlorine atoms and formic acid. Analysis of the spectra yields reliable estimates of the rotational, centrifugal distortion and spin–rotational parameters describing the ground state of this species. The rotational constants derived for HOCO and DOCO are consistent with a planar equilibrium structure and are used to confirm that the carrier of the spectrum is the trans‐geometrical isomer.