Transient diode laser absorption spectroscopy of the ν2 fundamental of <i>trans</i>-HOCO and DOCO

Abstract

We report the observation and assignment of the ν2 fundamental vibration in the HOCO and DOCO radicals. The radical was made by the photolysis of acetic acid or acetic acid-d at 193 nm in a flow system. The observed spectra indicate that the excited vibrational level is perturbed in both HOCO and DOCO. In HOCO, the rotational levels in ν2=1 have an irregular dependence on the Ka quantum number, probably caused by anharmonic interactions with combinations of lower frequency in plane vibrations. An a-type Coriolis interaction involving perturbation by a level containing one quantum of the out-of-plane torsional vibration cannot be rigorously excluded however. In DOCO, there are also N-dependent perturbations in the excited state. Only parallel transitions were assigned in the ν2 fundamental of both isotopomers. The K=0 band origin for HOCO is at 1852.567 cm−1 which compares with 1843.7 cm−1 reported previously for the radical trapped in a low-temperature argon matrix. This absorption spectrum will be useful in future studies of chemical reactions involving the radical.