Fourier transform microwave spectroscopy of HZnCN (X ¹Σ ⁺) and ZnCN (X ²Σ⁺)

The pure rotational spectrum of HZnCN in its X ¹Σ ⁺ + electronic state has been recorded using pulsed Fourier transform microwave (FTMW) techniques in the frequency range 7-39 GHz-the first spectroscopic study of this species in the gas phase. The FTMW spectrum of ZnCN (X ²Σ⁺) has been measured as well. A new FTMW spectrometer with an angled beam and simplified electronics, based on a cryopump, was employed for these experiments. The molecules were created in a dc discharge from a gas mixture of Zn (CH₃) ₂ and cyanogen (1% D2 for the deuterated analogs), diluted with argon, that was expanded supersonically from a pulsed nozzle. Seven isotopologues of HZnCN arising from zinc, deuterium, and C 13 substitutions were studied; for every species, between three and five rotational transitions were recorded, each consisting of numerous hyperfine components arising from nitrogen, and in certain cases, deuterium, and 67-zinc nuclear spins. Four transitions of ZnCN were measured. From these data, rotational, nuclear spin-rotation, and quadrupole coupling constants have been determined for HZnCN, as well as rotational, and magnetic and quadrupole hyperfine parameters for the ZnCN radical. The bond lengths determined for HZnCN are rH-Zn =1.495 Å, rZn-C =1.897 Å, and rC-N =1.146 Å, while those for ZnCN are rZn-C =1.950 Å and rC-N =1.142 Å. The zinc-carbon bond length thus shortens with the addition of the H atom. The nitrogen quadrupole coupling constant eqQ was found to be virtually identical in both cyanide species (-5.089 and -4.931 MHz), suggesting that the electric field gradient across the N nucleus is not influenced by the H atom. The quadrupole constant for the Z 67 n nucleus in H Z 67 nCN is unusually large relative to that in Z 67 nF (-104.578 versus -60 MHz), evidence that the bonding in the cyanide has more covalent character than in the fluoride. This study additionally suggests that hydrides of other metal cyanide species are likely candidates for high resolution spectroscopic investigations.