Ab-initio calculations of the electronic structure and properties of the diatomic zinc monohalides ZnX (X=F, Cl, Br, I)

The pure rotational spectrum of the ZnBr radical (X2Σ+): Trends in the zinc halide series

The pure rotational spectrum of ZnBr (X²Σ⁺) has been recorded in the frequency range 259-310 GHz using millimeter-wave direct absorption techniques. This study is the first quantitative spectroscopic investigation of this free radical. ZnBr was synthesized in a DC discharge by the reaction of zinc vapor in argon with one of three reagents: BrCH₃, Br₂CH₂, or Br₂. Eight rotational transitions were measured for six isotopologues (⁶⁴Zn⁷⁹Br, ⁶⁴Zn⁸¹Br, ⁶⁶Zn⁷⁹Br, ⁶⁶Zn⁸¹Br, ⁶⁸Zn⁷⁹Br, and ⁶⁸Zn⁸¹Br), all of which exhibited spin-rotation interactions. Furthermore, transitions originating in the v = 1 through 3 excited vibrational states were obtained for certain isotopologues. Five rotational transitions were also recorded for ⁶⁷Zn⁷⁹Br, in which hyperfine splittings were observed arising from the ⁶⁷Zn nucleus (I = 5/2). The spectra were analyzed using a Hund's case (b_βJ) Hamiltonian, and rotational, spin-rotation, and ⁶⁷Zn magnetic hyperfine constants were determined. Equilibrium parameters were also derived for the ⁶⁴Zn⁷⁹Br, ⁶⁴Zn⁸¹Br, ⁶⁶Zn⁷⁹Br, and ⁶⁶Zn⁸¹Br isotopologues, including the vibrational constant, ω_e = 286 cm^-1. The equilibrium bond length was derived to be r_e = 2.268 48(90) Å. Analysis of the ⁶⁷Zn hyperfine parameters suggest a decrease in ionic character in ZnBr from the other known zinc halides, ZnF and ZnCl.

Electronic structure with dipole moment and ionicity calculations of the low-lying electronic states of the ZnF molecule

Adiabatic potential energy curves of the 28 low-lying doublet and quartet electronic states in the representation 2s+1Λ(±) of the zinc monofluoride molecule are investigated using the complete active space self-consistent field (CASSCF) with multi-reference configuration interaction (MRCI) method including single and double excitations with the Davidson correction (+Q). The internuclear distance Re, the harmonic frequency ωe, the static and transition dipole moment μ, the rotational constant Be, and the electronic transition energy with respect to the ground state Te are calculated for the bound states. The transition dipole moment between some doublet states is used to determine the Einstein spontaneous A21 and induced emission [Formula: see text] coefficients, as well as the spontaneous radiative lifetime τspon, emission wavelength λ21, and oscillator strength f21. The ground state ionicity qionicity and equilibrium dissociation energy DE,e are also computed. The comparison between the values of the present work and those available in the literature for several electronic states shows very good agreement. Twenty-three new electronic states have been studied in the present work for the first time.

Structure and energetics of gaseous HZnCl

The HZnCl molecule has recently been observed both in the gas phase and in argon matrixes, and the complexity of its spectrum has created big discrepancies between experimental and theoretically predicted Zn-H bond distances. In an attempt to resolve the questionable H-ZnCl bond length issue, as well as to study its stability relative to bond breakage, we have investigated at a very high ab initio level its geometric and energetic parameters. At the coupled cluster level of theory [CCSD(T)] with the new correlation-consistent basis sets for Zn by Balabanov and Peterson, and with the inclusion of core/valence and one-electron Douglas-Kroll-Hess relativistic effects, the basis set extrapolated H-ZnCl and HZn-Cl bond lengths have been calculated to be 1.499 and 2.079 A, compared with the experimental estimates of 1.596-1.789 and 2.08346 A, respectively. With the same procedure, the experimentally unknown bond length of ground-state ZnCl has been found to be equal to 2.122 A. As in the free diatomics ZnCl and ZnH, the HZn-Cl bond is stronger than the H-ZnCl bond by about 30 kcal/mol.

Completing the 3d metal fluoride series: The pure rotational spectrum of ZnF (XΣ+2)

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 (64ZnF, 66ZnF, 67ZnF, 68ZnF, and 70ZnF) in the ground and several excited vibrational (v=1, 2, and 3) states. Each transition consists of spin-rotation doublets with a splitting of approximately 150 MHz, indicating that the electronic ground state of ZnF is 2Sigma+, as predicted by theory. Fluorine hyperfine splitting was observed in three isotopologues (64ZnF, 66ZnF, and 67ZnF), and hyperfine structure from the zinc-67 nucleus (I=52) was additionally resolved in 67ZnF. Rotational, fine structure, and 19F and 67Zn hyperfine constants were determined for ZnF, as well as equilibrium parameters. The bond length of the main isotopologue 64ZnF was calculated to be re=1.7677 A. Evaluation of the hyperfine constants indicates that the sigma orbital containing the unpaired electron is approximately 80% 4s(Zn) in character with approximately 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.