Corey J. Evans

The microwave spectra and structures of Ar–AgX (X=F,Cl,Br)

The rotational spectra of the complexes Ar–AgF, Ar–AgCl, and Ar–AgBr have been observed in the frequency range 6–20 GHz using a pulsed jet cavity Fourier transform microwave spectrometer. All the complexes are linear and rather rigid in the ground vibrational state, with the Ar–Ag stretching frequency estimated as ∼140 cm−1. Isotopic data have been used to calculate an r0 structure for Ar–AgF, while for Ar–AgCl and Ar–AgBr partial substitution structures have also been obtained. To reduce zero-point vibrational effects a double substitution method (rd) was employed to calculate the structures of Ar–AgCl and Ar–AgBr. The Ar–Ag bond distance has been found to be rather short and to range from 2.56 A in Ar–AgF to 2.64 A in Ar–AgBr. Ab initio MP2 and density functional theory calculations for Ar–AgF and Ar–AgCl model the geometries and stretching frequency well, and predict an Ar–Ag bond energy in Ar–AgF of ∼23 kJ mol−1. These results indicate that the Ar–AgX complexes are more strongly bound than typical van...

Noble gas–metal chemical bonding: the microwave spectra, structures and hyperfine constants of Ar–AuF and Ar–AuBr

The rotational spectra of the complexes Ar–AuF and Ar–AuBr have been observed in the frequency range 7–22 GHz using a pulsed-jet cavity Fourier transform microwave spectrometer. Both complexes are linear and rather rigid in the ground vibrational state, with the Ar–Au stretching frequency estimated as ∽200 cm−1. Isotopic data have been used to calculate an r0 structure for Ar–AuBr while for Ar–AuF only an estimation of the r0 geometry could be made. Ab initio calculations at the MP2 level of theory model the geometries and stretching frequencies well and predict an Ar–Au bond energy in Ar–AuF of ∽60 kJ mol−1. The Au nuclear quadrupole coupling constant changes significantly on complex formation, indicating extensive charge arrangement. This in conjunction with the large dissociation energy and ab initio results show that the Ar–Au bonds in these complexes are weakly covalent in nature.

The pure rotational spectrum of ScBr

The pure rotational spectra of Sc79Br and Sc81Br have been measured in two vibrational states (v=0 and 1) in the 5–24 GHz spectral region, using a cavity pulsed jet Fourier transform microwave spectrometer. The samples were prepared by ablating Sc metal in the presence of Br2 contained in the Ar backing gas of the jet. The equilibrium internuclear distance re has been determined along with estimates for the harmonic vibration frequency ωe and the dissociation energy, De. Nuclear quadrupole coupling constants and spin–rotation constants have been determined for both Sc and Br. The ionic character of the ScBr bond is estimated to be ∽95%. Magnetic shieldings for both nuclei have been estimated.

PURE MW DATA FOR v=0−6 OF PbI GIVE VIBRATIONAL SPACINGS AND A FULL ANALYTIC POTENTIAL ENERGY FUNCTION

At last year’s ISMS meeting, Zaleski et al. reported new broadband MW spectroscopy measurements of pure rotational transitions in the v = 0 − 6 levels of the Π1/2 ground electronic state of PbI.a The analysis presented at that time was a conventional v-level by v-level ‘band-constant’ analysis performed using the PGopher program.b That level-bylevel PGopher analysis yielded values of Bv , Dv and five spin-splitting parameters for each vibrational level of each isotopologue. Ignoring the spin-splitting information, the Bv and Dv values were used to generate a set of synthetic pure R(0) transitions for each level that were taken to represent the “mechanical” information about the molecule contained in these spectra. A standard direct-potential-fit (DPF) analysisc was then used to fit these data to an “Expanded Morse Oscillator” (EMO) potential function form. The well-depth parameter De was fixed at the literature value, while values of the equilibrium distance re and three EMO exponent-coefficient expansion ‘potential shape’ parameters are determined from the fits. The best fits to the data yield potentials whose fundamental vibrational spacings are in excellent agreement with experimentd together with reliable predictions for the first five overtone energies.