A new set of covalent atomic radii has been deduced from crystallographic data for most of the elements with atomic numbers up to 96. The proposed radii show a well behaved periodic dependence that allows us to interpolate a few radii for elements for which structural data is lacking, notably the noble gases. The proposed set of radii therefore fills most of the gaps and solves some inconsistencies in currently used covalent radii. The transition metal and lanthanide contractions as well as the differences in covalent atomic radii between low spin and high spin configurations in transition metals are illustrated by the proposed radii set.

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Covalent radii revisited

The Cologne Database for Molecular Spectroscopy, CDMS: a useful tool for astronomers and spectroscopists

The available data on the van der Waals radii of atoms in molecules and crystals are summarized. The nature of the continuous variation in interatomic distances from van der Waals to covalent values and the mechanisms of transformations between these types of chemical bonding are discussed.

Van der Waals Radii of Elements

A family of segmented all-electron relativistically contracted (SARC) basis sets for the elements Hf−Hg is constructed for use in conjunction with the Douglas−Kroll−Hess (DKH) and zeroth-order regular approximation (ZORA) scalar relativistic Hamiltonians. The SARC basis sets are loosely contracted and thus offer computational advantages compared to generally contracted relativistic basis sets, while their sufficiently small size allows them to be used in place of effective core potentials (ECPs) for routine studies of molecules. Practical assessments of the SARC basis sets in DFT calculations of atomic (ionization energies) as well as molecular properties (geometries and bond dissociation energies for MHn complexes) confirm that the basis sets yield accurate and reliable results, providing a balanced description of core and valence electron densities. CCSD(T) calculations on a series of gold diatomic compounds also demonstrate the applicability of the basis sets to correlated methods. The SARC basis sets ...

All-Electron Scalar Relativistic Basis Sets for Third-Row Transition Metal Atoms.

A description and summary of the latest edition of the AFGL high-resolution transmission molecular absorption database (HITRAN) parameters are presented. This new database combines the information for the seven principal atmospheric absorbers and twenty-one additional molecular species previously contained on the AFGL atmospheric absorption line parameter compilation and on the trace gas compilation. In addition to updating the parameters on earlier editions of the compilation, new parameters have been added to this edition such as the self-broadened half-width, the temperature dependence of the air-broadened half-width, and the transition probability. The database contains 348,043 entries between 0 and 17,900/cm. A FORTRAN program is now furnished to allow rapid access to the molecular transitions and for the creation of customized output. A separate file of molecular cross sections of 11 heavy molecular species, applicable for qualitative simulation of transmission and emission in the atmosphere, has also been provided.

The HITRAN database: 1986 edition.

The rotational spectra of the complexes Ar–CuF, Ar–CuCl, and Ar–CuBr have been observed in the frequency range 5–22 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–Cu stretching frequency estimated as ∼200 cm−1. Isotopic data have been used to calculate an r0 structure for Ar–CuF, while for Ar–CuCl and Ar–CuBr partial substitution structures have also been obtained. To reduce zero-point vibrational effects a double substitution method (rd) has also been employed to calculate the structures of Ar–CuCl and Ar–CuBr. The Ar–Cu distance has been found to be rather short and to range from 2.22 A in Ar–CuF to 2.30 A in Ar–CuBr. Ab initio calculations at the MP2 level of theory model the geometries and stretching frequencies well and predict an Ar–Cu bond energy in Ar–CuF of ∼47.3 kJ mol−1. Large changes in the Cu nuclear quadrupole coupling constant on complex formation show that extensive charge re...

Noble gas–metal chemical bonding? The microwave spectra, structures, and hyperfine constants of Ar–CuX(X=F, Cl, Br)

The pure rotational spectra of Ar−AuCl and Kr−AuCl have been measured using a pulsed-jet cavity Fourier transform microwave spectrometer. Both complexes have been found to be linear and are relatively rigid in their ground vibrational states. The noble gas−gold stretching frequencies have been estimated to be 198 and 161 cm-1 for Ar−AuCl and Kr−AuCl, respectively. From the isotopic data obtained, r0 structures have been calculated for both Ar−AuCl and Kr−AuCl, while a partial substitution (rs) structure has been obtained for Kr−AuCl. The Ar−Au distance has been found to be 2.47 A, while the Kr−Au distance is 2.52 A. Ab initio calculations have been performed at the MP2 level of theory on both complexes to obtain geometries, vibrational frequencies, and dissociation energies. The dissociation energies for Ar−AuCl and Kr−AuCl have been estimated to be 47 and 71 kJ mol-1, respectively. The nuclear quadrupole coupling constant of Au has been found to change significantly on complex formation (to −259.8 MHz in...

Noble Gas−Metal Chemical Bonds. Microwave Spectra, Geometries, and Nuclear Quadrupole Coupling Constants of Ar−AuCl and Kr−AuCl

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 der Waals complexes. Analysis of the halogen nuclear quadrupole coupling constants was unable to confirm whether extensive electron rearrangement occurs upon formation of the complexes.

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

Microwave spectra of the complexes KrAuF and KrAgBr have been measured for the first time using a cavity pulsed jet Fourier transform microwave spectrometer. The samples were prepared by laser ablation of the metal from its solid and allowing the resulting plasma to react with an appropriate precursor (Kr, plus SF6 or Br2) contained in the backing gas of the jet (usually Ar). Rotational constants; geometries; centrifugal distortion constants; vibration frequencies; and 197Au, 79Br, and 81Br nuclear quadrupole coupling constants have all been evaluated. The complexes are unusually rigid and have short Kr−Au and Kr−Ag bonds. The 197Au nuclear quadrupole coupling constant differs radically from its value in an AuF monomer. In addition 83Kr hyperfine structure has been measured for KrAuF and the previously reported complex KrAgF. The geometry of the latter has been reevaluated. Large values for the 83Kr nuclear quadrupole coupling constants have been found for both complexes. Both the 197Au and 83Kr hyperfine...

Microwave spectra and structures of KrAuF, KrAgF, and KrAgBr; 83Kr nuclear quadrupole coupling and the nature of noble gas-noble metal halide bonding.

XeCu covalent bonding has been found in the complexes XeCuF and XeCuCl. The molecules were characterized by Fourier transform microwave spectroscopy, supported by MP2 ab initio calculations. The complexes were prepared by laser ablation of Cu in the presence of Xe and SF6 or Cl2 and stabilized in supersonic jets of Ar. The rotational constants and centrifugal distortion constants show the XeCu bonds to be short and rigid. The 131Xe, Cu, and Cl nuclear quadrupole coupling constants indicate major redistributions of the electron densities of Xe and CuF or CuCl on complex formation which cannot be accounted for by simple electrostatic effects. The MP2 calculations corroborate the XeCu bond lengths and predict XeCu dissociation energies ∼50−60 kJ mol-1. The latter cannot be accounted for in terms of induction energies. The MP2 calculations also predict valence molecular orbitals with significant shared electron density between Xe and Cu and negative local energy densities at the XeCu bond critical points. All...

Michael C. L. Gerry

Papers

Noble gas–metal chemical bonding? The microwave spectra, structures, and hyperfine constants of Ar–CuX(X=F, Cl, Br)

Noble Gas−Metal Chemical Bonds. Microwave Spectra, Geometries, and Nuclear Quadrupole Coupling Constants of Ar−AuCl and Kr−AuCl

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

Microwave spectra and structures of KrAuF, KrAgF, and KrAgBr; 83Kr nuclear quadrupole coupling and the nature of noble gas-noble metal halide bonding.

XeCu covalent bonding in XeCuF and XeCuCl, characterized by fourier transform microwave spectroscopy supported by quantum chemical calculations.