Synchrotron-based rotation-vibration spectroscopy of imidazole

We report the observation of the far-infrared absorption spectra of the ν21, ν20, ν19, ν18 and ν17 bands of imidazole in the 480–840 cm−1 range, taken at the Canadian Light Source using synchrotron radiation. The ν21, ν18 and ν17 bands were rotationally assigned and analyzed. Observations of the ν20 and ν19 bands were limited to their dense, unresolved Q branches. The analysis provided accurate origins for all five bands, and a first rotational characterization of the ν18 and ν17 levels, as well as a global fit that includes data from recent microwave experiments on the ground vibrational state and low-lying excited vibrational levels (Guiliano et al., 2019; Arenas et al., 2021).