Far-Infrared Synchrotron Spectroscopy and Quantum Chemical Calculations of the Potentially Important Interstellar Molecule, 2-Chloroethanol

Abstract

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.

Far-Infrared Synchrotron Spectroscopy of a Potentially Important Interstellar Isotopologue of Vinyl Alcohol: CH2CHOD

“…The successful production of monodeuterated 2-chloroethanol is evident from the shift in the ν 20 torsional band of the most stable rotamer of 2-chloroethanol (Gg′); , this shift is from 344.2 to 240.6 cm –1 , which is consistent with the relation, = 243 cm –1 . As shown in Figure , we observed a marked gradual decrease in the deuterated 2-chloroethanol precursor peak as we increased the pyrolysis temperature from 800 to 950 °C.…”

“…Band Assignment and Torsional Analysis. The successful production of monodeuterated 2-chloroethanol is evident from the shift in the ν 20 torsional band of the most stable rotamer of 2-chloroethanol (Gg′); 41,42 this shift is from 344.2 to 240.6 cm −1 , which is consistent with the relation,…”

Computational Evidence Suggests That 1-Chloroethanol May Be an Intermediate in the Thermal Decomposition of 2-Chloroethanol into Acetaldehyde and HCl

“…It is clear from this figure that the most affected band is the HOC torsion plus OH stretching combination band appearing in the far-infrared below 500 cm –1 . In our ωB97X-D/cc-pVTZ calculations, the band appears at 376 cm –1 for the Gg′ rotamer, while experimentally it was recorded at 344.0 cm –1 by Durig et al and 344.2 cm –1 by Soliday et al The analogous bands in Tg and Tt were obtained by us at 326 and 290 cm –1 respectively, while Durig et al reported them experimentally at 281 and 200 cm –1 , respectively. The discrepancy between our values and the experimental ones is probably due to anharmonic effects.…”

“…This barrier, corresponding to the transition state TS12, is however 15% larger than the barrier for the transformation of 2ClEtOH to anti -VA (57.1 vs 48.7 kcal mol –1 ). The reverse barrier (i.e., that for the reaction HCl + HOCH 2 CH 2 OH → ClCH 2 CH 2 OH + H 2 O) was calculated simultaneously to this work by Soliday et al, who found a value of 52 kcal mol –1 at the MP2/cc-pVTZ level, in agreement with our own value of 53.4 kcal mol –1 .…”

Twenty years of exceptional success: The molecular education and research consortium in undergraduate computational chemistry (MERCURY)

“…The faculty published 2 peer‐reviewed books, [ 238,239 ] 9 peer‐reviewed book chapters, [ 240–248 ] and 115 peer‐reviewed research papers. [ 249–363 ] This comes to 1.6 peer‐reviewed products/faculty/year during the 3‐year grant period, which is 3.2 times the rate of publication for natural science faculty at PUIs. [ 46 ]…”