Completing the 3d metal fluoride series: The pure rotational spectrum of ZnF (X²∑⁺)

The pure rotational spectrum of the ZnF radical has been recorded in the range of 176-527 GHz using millimeter/submillimeter direct absorption techniques. This study is the first gas-phase spectroscopic investigation of this species. Between 5 and 11 transitions were measured for each of five isotopologues of this radical (Zn64 F, Zn66 F, Zn67 F, Zn68 F, and Zn70 F) in the ground and several excited vibrational (v=1, 2, and 3) states. Each transition consists of spin-rotation doublets with a splitting of ∼150 MHz, indicating that the electronic ground state of ZnF is +2, as predicted by theory. Fluorine hyperfine splitting was observed in three isotopologues (Zn64 F, Zn66 F, and Zn67 F), and hyperfine structure from the zinc-67 nucleus (I=52) was additionally resolved in Zn67 F. Rotational, fine structure, and F19 and Zn67 hyperfine constants were determined for ZnF, as well as equilibrium parameters. The bond length of the main isotopologue Zn64 F was calculated to be re =1.7677 Å. Evaluation of the hyperfine constants indicates that the orbital containing the unpaired electron is ∼80% 4s (Zn) in character with ∼10% contributions from each of the 2p (F) and 4p (Zn) orbitals. These results imply that ZnF is somewhat less ionic than CaF, as suggested by theory.