Ab initio ro-vibrational spectroscopy of the group 11 cyanides: CuCN, AgCN, and AuCN.

Accurate near-equilibrium potential energy and dipole moment functions have been calculated for the linear coinage-metal cyanides CuCN, AgCN, and AuCN using coupled cluster methods and sequences of correlation consistent basis sets. The explicitly correlated CCSD(T)-F12b method is used for the potential energy surfaces (PESs) with inclusion of core correlation, and is combined with contributions from molecular spin-orbit coupling, scalar relativity, and effects due to higher order electron correlation. The resulting composite PESs are used in both perturbative and variational calculations of the ro-vibrational spectra. In addition to accurate equilibrium geometries, the ro-vibrational spectra are predicted, which are found to be relatively intense in the 200-600 cm(-1) range due to the bending and metal-carbon stretching modes. The CN stretch near 2165 cm(-1) is also predicted to carry enough intensity to allow its observation by experiment. A strong Fermi-resonance is predicted between the first overtone of the bend and the fundamental of the metal-carbon stretch for both CuCN and AgCN. The heats of formation at 0 K are predicted from their calculated atomization energies to be 89.8, 88.6, and 104.5 kcal  mol(-1) for CuCN, AgCN, and AuCN, respectively.