Rotational spectroscopy of 3d transition-metal cyanides:: Millimeter-wave studies of ZnCN (X2Σ+)

The pure rotational spectrum of the ZnCN radical in its X (2)Sigma(+) ground electronic state has been recorded using millimeter/sub-mm direct absorption techniques in the range 339-543 GHz. This work is the first spectroscopic observation of this molecule, which was created by the reaction of zinc vapor and cyanogen gas in a dc discharge. Twenty-one rotational transitions were recorded for the main zinc isotopomer, (ZnCN)-Zn-64, in its ground vibrational state, as well as 8-16 transitions for the Zn-66, Zn-68, and C-13 isotopomers. Data was also obtained for ZnCN in several quanta of its bending mode and in the (100) stretching vibration. These measurements indicate that the most stable form of zinc and the cyanide moiety is the linear cyanide structure, as has also been found for copper and nickel. In contrast, the linear isocyanide geometry is lowest in energy for gallium and aluminum. A spectroscopic analysis has been carried out of the (000) and excited vibrational data, establishing rotational, spin-rotation, and l-type doubling parameters. Several structures (r(0), r(s), and r(m)((1))) have been determined for ZnCN as well, along with estimates of the heavy-atom stretch (omega(1)), and bending (omega(2)) frequencies. These calculations suggest that the metal-carbon bond in ZnCN is weaker than in CuCN or NiCN. The tendency of these metals to form the linear cyanide geometry, as opposed to the linear isocyanide or T-shaped structures, is additionally discussed. (C) 2002 American Institute of Physics.