Far-Infrared Synchrotron Spectroscopy and Quantum Chemical Calculations of the Potentially Important Interstellar...

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 ν₁₉ 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 ν₁₉ 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.