Far-infrared Spectroscopic Characterization of Anti-vinyl Alcohol

We report a detailed analysis of the high-resolution far-infrared spectrum of anti-vinyl alcohol, which has been previously identified toward Sagittarius B2(N). The ν ₁₅ OH torsional fundamental investigated here is more than 200 cm^-1 removed from the next nearest vibration, making it practically unperturbed and ideal to help refine the ground state rotational constants that were previously determined from 25 microwave lines. We assigned 1335 lines within the ν ₁₅ fundamental centered at 261.5512 cm^-1, with J and K _a ranges of 1-59 and 0-16, respectively. The microwave and far-infrared line positions were fit with Watson-type A- and S-reduced Hamiltonians, with the inclusion of quartic and select sextic distortion terms. This resulted in a significant refinement of the ground state constants, in addition to the determination of the {ν }₁₅=1 state constants for the first time. The spectroscopic parameters are in good agreement with the results from anharmonic coupled-cluster calculations, and should be useful in searches for rotationally and/or vibrationally warm anti-vinyl alcohol in interstellar molecular clouds.