The pure rotational spectrum of the organozinc halide, ClZnCH 3 ( X 1 A 1 ), has been measured using Fourier-transform microwave (FTMW) and millimeter-wave direct-absorption methods in the frequency range 10–296 GHz. This work is the first study of ClZnCH 3 by gas-phase spectroscopy. The molecule was created in a DC discharge from the reaction of zinc vapor, produced either by a Broida-type oven or by laser ablation, with chloromethane in what appears to be a metal insertion process. Rotational and chlorine quadrupole constants were determined for three zinc isotopologues. The Zn Cl bond was found to be partly ionic and significantly shorter than in EtZnCl. [ABSTRACT FROM AUTHOR]