Molecular Structures of Hydrogen Cyanide and Acetonitrile as Studied by Gas Electron Diffraction

The structures of HCN and CH3CN have been determined by gas electron diffraction for a critical comparison between diffraction and spectroscopic data. For HCN, the rg(C≡N), determined by gas electron diffraction, 1.158±0.003 Å, is consistent within the estimated limit of experimental error with that calculated from the spectroscopic re structure and the harmonic and anharmonic force constants by a perturbation procedure, 1.1588 Å. For CH3CN, electron diffraction intensities have been analyzed jointly with the rotational constants for the normal and three deuterated species determined by microwave spectroscopy by Kessler et al. and Thomas et al. The isotopic difference in the average C–H distance, δr=rav(C–H)–rav(C–D), has also been treated as one of the independent parameters. The analysis has led to the following structure: rg(C≡N)=1.159±0.002 Å, rg(C–C)=1.468±0.002Å, rg(C–H)=1.107±0.004 Å, ∠C–C–H (rav)=109.7±0.2° and δr=0.001±0.002 Å.