The pure rotational spectrum of the NiCN radical (X 2Δi) has been recorded using millimeter/sub-mm direct absorption techniques in the range 360–550 GHz. Transitions arising from four nickel isotopomers (58Ni,60Ni,62Ni,64Ni) and Ni58CN13 were observed in the ground vibrational state, as well as lines originating in the v2 bending and v1 stretching modes. In the vibrational ground state, transitions from both spin–orbit components (Ω=52 and 32) were identified; in the Ω=32 ladder, significant lambda-doubling was observed. Multiple vibronic components were found for each bending quantum recorded, a result of Renner–Teller interactions. These components were only observed in the lower spin–orbit ladder (Ω=52), however, suggesting that spin–orbit coupling dominates the vibronic effects. The ground-state data were analyzed with a case (a) Hamiltonian, generating rotational, spin–orbit, and lambda-doubling constants for NiCN58 and NiCN60. The vibrationally excited lines were modeled with effective rotational parameters, except where a case (c) or case (b) coupling scheme could be meaningfully used. From the ground-state rotational parameters, r0, rs, and rm(1) structures were derived as well. NiCN appears to be a covalently bonded molecule with similar properties to NiH.

Alkali metal amides typically aggregate in solution and the solid phase, and even in the gas phase. In addition, even in the few known monomeric structures, the coordination number of the alkali metal is raised by binding of Lewis-basic solvent molecules, with concomitant changes in structure. In contrast, the simplest lithium amide LiNH(2) has never been made in a monomeric form, even though its structure has been theoretically predicted several times. Here, the first experimental structural data for a monomeric, unsolvated lithium amide are determined using a combination of gas-phase synthesis and millimeter/submillimeter-wave spectroscopy. All data point to a planar structure for LiNH(2). The r(o) structure of LiNH(2) has a Li-N distance of 1.736(3) A, an N-H distance of 1.022(3) A, and a H-N-H angle of 106.9(1) degrees. These results are compared with theoretical predictions for LiNH(2), and experimental data for oligomeric, solid-phase samples, which could not resolve the question of whether LiNH(2) is planar or not. In addition, comparisons are made with revised gas-phase and solid-phase data and calculated structures of NaNH(2).

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The pure rotational spectrum of the CoCN radical has been recorded in the frequency range 350-500 GHz using direct absorption techniques. This study is the first spectroscopic observation of this molecule by any experimental technique. Spectra of Co (13)CN have been measured as well. These data indicate that this species is linear in its ground electronic state and has the cyanide, as opposed to the isocyanide, geometry. The ground state term has been assigned as (3)Phi(i), based on the measurement of three spin components (Omega=4, 3, and 2) and in analogy to other isovalent cobalt-bearing species. Hyperfine splittings resulting from the (59)Co nuclear spin of I=7/2 were observed in every transition, each of which exhibited an octet pattern. For the lowest energy spin component, Omega=4, vibrational satellite features were also identified arising from the first quantum of the Co-C (v(1)=1) stretch and the v(2)=1 and v(2)=2 quanta of the bending mode, which were split by Renner-Teller interactions. The ground state measurements of CoCN were analyzed with a case a(beta) Hamiltonian, establishing rotational, fine structure, and hyperfine parameters. The vibrational and Co (13)CN spectra for the Omega=4 component were fit as well. An r(0) structure was also calculated, providing estimates of the Co-C and C-N bond distances, based on the Omega=4 transitions. CoCN is the fourth molecule in the 3d transition metal series to exhibit the linear cyanide structure, along with the Zn, Cu, and Ni analogs. The preference for this geometry, as opposed to the isocyanide form, may indicate a greater degree of covalent bonding in these species.