The pure rotational spectrum of ZnCl (X2Σ+): Variations in zinc halide bonding

The radical ZnCl (X2Σ+) has been studied using millimeter-wave direct-absorption techniques. Pure rotational spectra of 67Zn35Cl, 66Zn37Cl, 68Zn35Cl, 64Zn35Cl, 64Zn37Cl, and 66Zn35Cl were measured in the vibrational ground state and data were also recorded for the latter three in the v = 1 and v = 2 states. Every rotational transition was found to be split into a doublet due to spin-rotation interactions. For 67Zn35Cl, each doublet exhibited additional splittings arising from hyperfine coupling of the 67Zn (I = 5/2) nucleus. Rotational, fine structure, and hyperfine constants have been determined from these data, and equilibrium parameters calculated. The equilibrium bond length of 64Zn35Cl is found to be 2.13003305(24) Å, in good agreement with recent theoretical predictions. Interpretation of hyperfine constants indicates that the 12σ orbital is ∼70% Zn(4s) in character, suggesting that the zinc chloride bond is relatively ionic.