Structure, Vibrational Spectra, Dipole Moment, and Stability of Gaseous LiCN and LiNC

An ab initio Hartree–Fock calculation of the structure of gaseous LiCN and LiNC has been performed using a basis set of 84 uncontracted and 45 contracted Gaussian atomic functions. The calculated Li–C distance is 3.6317 a.u.; the calculated C–N distance is 2.1915 a.u. for linear LiCN. For linear LiNC the calculated Li–N distance is 3.3354 a.u.; the calculated N–C distance is 2.1857 a.u. No experimental gas‐phase data have been reported, but the calculated C–N and N–C distances agree well with experimental C≡N bond lengths in other molecules. The calculated linear stretching mode frequencies are ${\nu }_1{\text{\hspace{0.17em}≈\hspace{0.17em}2375, ν}}_2\text{\hspace{0.17em}≈\hspace{0.17em}670}{\mathrm{cm}}^{\text{−1}}$ (⁶Li¹²C¹⁴N), and ${\nu }_1{\text{\hspace{0.17em}≈\hspace{0.17em}2367, ν}}_2\text{\hspace{0.17em}≈\hspace{0.17em}785}{\mathrm{cm}}^{\text{−1}}$ (⁶Li¹⁴N¹²C), agreeing with ${\nu }_1\text{\hspace{0.17em}≈\hspace{0.17em}2250}{\mathrm{cm}}^{\text{−1}}$ for other molecules. For linear ⁶Li¹⁴N¹²C, a bending mode frequency of ≈ 250 cm⁻¹ was calculated. The predicted dipole moment is very high (3–4 a.u.). A marginal energy difference of 0.0141 a.u. between LiCN and LiNC was found, LiNC being the more stable.