Rotational and vibrational spectra of ethynol from quantum-mechanical calculations

Abstract

Ethynol, HCCOH, has not been observed despite a theoretical prediction of its stability to tautomerization to ketene. Identification of this unknown molecule, either in space or in the laboratory, can be aided by ab initio calculation of spectroscopic parameters. At the HP/3-21G level, harmonic vibrational frequencies were computed via analytic second differentiation of the Hartee-Fock (HF) energy with respect to the nuclear coordinates. After application of an empirical scale factor, the resultant frequencies are (in cm-1) 473, 517, 773, 841, 1003, 1217, 2206, 3285, and 3418. At the CISD/DZ+P level, the computed dipole moment is 1.79 D. At the CISD+Q/DZ+P level, the molecule's rotational constants were determined. After scaling by empirical correction factors they were used to derive the 404 → 303 frequency of 76.81 ± 0.3 GHz with a triplet splitting (414 → 313 and 413 → 312 relative to the 404 → 303 transition as the central line) of 0.30 ± 0.01 GHz. © 1982 American Chemical Society.