The millimeter wave rotational spectrum of lactic acid

The results of a comprehensive investigation of the rotational spectrum of lactic acid over the frequency region 171-318 GHz are reported. Some supersonic expansion measurements at 8-16 GHz have also been made. A complete set of octic level constants in the asymmetric rotor Hamiltonian has been determined for the ground vibrational state from a fit to over 1000 measured transition frequencies. Spectroscopic constants have also been determined for the first five excited states of the low frequency, 60 cm−1, torsional vibrational mode, and for four other vibrationally excited states. Vibrational states become rather crowded above 200 cm−1, with seven different states only in the next 100 cm−1, and almost all of the measured states in this energy region show evidence of perturbations. The analysis was carried out with the newly developed AABS software package for Assignment and Analysis of Broadband Spectra.