The pure rotational spectrum of CrCN (X ⁶∑⁺): An unexpected geometry and unusual spin interactions

The pure rotational spectrum of CrCN (X 6+) has been recorded in the frequency range 250-520 GHz using direct-absorption techniques. This is the first spectroscopic investigation of the CrCN radical. This species was synthesized by reacting Cr vapour with (CN)2. Spectra were obtained for the main isotopic species, the 53Cr and 13C isotopologues, and the heavy atom stretch and several quanta of the bending vibration. The molecule was found to have a linear cyanide geometry and a 6+ ground state. Rotational, fine structure, and l-type doubling constants have been determined. The spin-spin parametre was found to be small-a likely result of competing second-order spin-orbit contributions from excited 4-, 4, and 6 states. However, increased significantly in the bending mode, which may be caused by a reduction of the 6+-4 interaction strength due to spin-orbit vibronic coupling. In contrast, the value of , arising from interactions with a nearby 6state, was independent of v2. The CrCN bond lengths were determined to be rCr-C = 2.019 and rC-N = 1.148 . Delocalization of the 3d electrons into the CN 2* orbital, which is polarized towards the carbon atom, may account for the CrCN structure.