Millimeterwave rotational spectrum and theoretical calculations of cis-propionic acid

The millimeterwave rotational spectra of the cis conformer of propionic acid (C3H6O2) have been investigated in the ground vibrational state in the frequency range of 80.0–100.0 GHz. Many high J and K−1 (Jmax = 50, K−1 = 12) rotational lines have been assigned. A least-squares analysis of the measured and previously reported rotational transition frequencies resulted in the determination of an improved set of rotational and centrifugal distortion (CD) constants of the molecule. Detailed MP2 and DFT calculations were also carried out with various functional and basis sets to evaluate the spectroscopic constants, dipole moment, and various structural parameters of cis-propionic acid and compared with the corresponding experimental values. Potential energy surface has been calculated to identify other probable conformers in this molecule.