We report far-infrared spectra (100−600 cm −1 ) covering the torsional bands of the important interstellar molecule, vinyl alcohol. We observed the fundamental and first two hot bands of syn-vinyl alcohol and the fundamental and first hot band of anti-vinyl alcohol, whose infrared spectrum has not been previously reported. The hot bands for syn-vinyl alcohol were incrementally shifted by ∼40 cm −1 from the fundamental, implying a high degree of anharmonicity in the torsional potential in the vicinity of the global minimum. The opposite holds true for anti-vinyl alcohol, as evidenced by the relatively small red shift (∼2 cm −1 ) of the hot band with respect to the fundamental. These characteristics were captured by ab initio calculations of the torsional potential, which we fit a seven-term Fourier series expansion to, and used along with the calculated torsional inertias to solve for the energy levels and wave functions. The potential was empirically refined by fitting the three leading terms in the expansion to the observed torsional frequencies, which resulted in a 3-fold decrease in the root-mean-square deviation between theory and experiment. The resulting energy difference between the ground states of the two rotamers is 4.0 kJ/mol, which is approximately consistent with the measured intensity ratio of the two ground-state torsional bands and with microwave spectroscopic measurements (4.5 ± 0.6 kJ/mol) [

The empirically derived assignment of the strongly interacting 51 and 92 vibrational states of trans-HCOOH has recently been reassigned on the basis of anharmonic frequency calculations, and this, in turn, affects the assignment of many higher energy states. Here, we investigate the high-resolution synchrotron-based torsional spectrum of trans-HCOOH, and find experimental confirmation that the proposed reassignment is indeed correct, i.e., that 92 is in fact lower in energy than 51. This is largely based on examining the intensity ratio of transitions with the same rotational quantum numbers between the 92-91 and 51-91 hot bands, which indicates that the 51 [92] state has ∼31% 92 [51] character. We also examined the torsional spectrum of trans-HCOOD, and find that the intensity ratios are consistent with 92 instead being higher in energy than 61 (which is analogous to 51 in trans-HCOOD), as previously determined from higher energy spectra.

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.

The high brightness of the Australian synchrotron allowed for detailed spectra to be collected at high resolution (0.00096 cm −1 ) in the vicinity of the a/b/c-type ν 19 band of 2-chloroethanol, which involves O−H torsional motion about the C−O bond. A rovibrational analysis was performed for both chlorine isotopologues in the ν 19 fundamental (centered at ∼344 cm −1 ) which involved the assignment of 7153 lines (J ≤ 90, K a ≤ 41). A global fit to these lines in addition to 119 microwave lines (J ≤ 29, K a ≤ 11) led to the determination of spectroscopic constants up to the sextic level in both the ground and excited states using Watson's A-reduction Hamiltonian. The constants agree well with those calculated at the anharmonic MP2/cc-pVTZ level and allow for spectroscopically accurate predictions of rotational transitions in the ground vibrational state to be made over a broad range of rotational energies (T R < 1000 K). We explored the role that 2-chloroethanol might play in interstellar molecular clouds by performing calculations on the substitution reaction between HCl and ethylene glycol, and the addition reaction between HCl and oxirane, all of which have been observed in Sagittarius B2(N) and are expected to play important roles in the chemistry that occurs on the icy mantles of interstellar dust grains. While both reactions have relatively high activation barriers, the HCl + oxirane reaction was found be much more exothermic; further calculations on it indicate that a water-like environment significantly reduces the barrier while slightly increasing its exothermicity. These results suggest that 2-chloroethanol could be efficiently produced from the cosmic ray bombardment of common interstellar ices.

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