G. L. Goodman

A systematic analysis of the spectra of the lanthanides doped into single crystal LaF3

The optical spectra of the lanthanides doped into single crystal LaF3 have been interpreted in terms of transitions within 4f N configurations. Energy matrices combining free‐ion terms with a crystal field for an approximate model which assumes C2v instead of the actual C2 site symmetry were diagonalized. Excellent correlations were obtained between experimental transition energies and the computed level structures. We also report the results of previously unpublished experimental spectroscopic investigations of Nd3+ and Sm3+:LaF3, as well as predicted energy levels for Pm3+:LaF3. The spectroscopic data for each ion were independently interpreted using an effective‐operator model, then the model parameters were intercompared. Systematic trends have been identified, and a comprehensive energy level diagram is presented.

Photoionization mass spectrometry of CH3SH, CD3SH, and CH3SD: Heats of formation of CH3S+(CH2SH+), CH2S+, CH2S, and HCS+

Photoionization yield curves have been obtained for the major ions from CH3SH. Auxiliary studies with selectively deuterated species reveal that CD3S+ has a slightly lower threshold than CD2SH+ from CD3SH; but CH2SD+ has a lower threshold than CH3S+ from CH3SD. An analysis of alternative interpretations is presented. The isotopic studies also imply that CH2S+ is more stable than HCSH+, and HCS+ is more stable than CSH+. The value ΔH°f,0(HCS+)≤259.2±0.9 kcal/mol obtained in this study is in good agreement with a bracketed proton affinity for CS, but differs significantly from a recent ab initio calculation. This result confirms the view that HCS+ can be formed in interstellar clouds by exothermic reactions. The reaction CH3S+/CH2SH+→HCS++H2 proceeds weakly at threshold, and much more strongly after overcoming an activation barrier of ∼0.9 eV.

Photoelectron spectra of the lanthanide trihalides and their interpretation

The He i photoelectron spectra of gaseous LaCl3, LaBr3, LaI3, CeBr3, CeI3, NdBr3, NdI3, ErI3, LuBr3, and LuI3 have been obtained. They display a pronounced increase in splitting, and hence a progressively clearer definition of peaks in the valence band as either the halogen or the lanthanide increases in atomic number. These experimental features, together with a refined relativistic Xα DVM calculation using the von Barth–Hedin potential, have enabled us to assign these peaks with confidence. The He ii photoelectron spectra of CeBr3, NdBr3, and LuI3 are also presented. They reveal that the 4f‐like ionizations of early lanthanide members (e.g., Ce) occur at lower energy than the ligand valence band, but that those of late members (e.g., Lu) are corelike. The aforementioned calculations reproduce this behavior quantitatively. They also help to rationalize a bimodal behavior in the valence band; the spectra with less than half‐filled 4f shell are very similar, as are those with more than half‐filled 4f shell...

Charge distributions and valency in copper oxide crystals related to superconductivity

We present an overview of the discrete variational method for calculating orbital states of a molecular cluster in the local density approximation. Then we introduce a new method of embedding a finite molecular cluster in a crystal lattice. This new technique of cluster weighting is based on the bulk stoichiometry of the crystal and the Mulliken populations for chemically complete atoms—those atoms that have all their covalently bonded nearest neighboring atoms also in the cluster. We have applied our new approach to calculate linear‐combination‐of‐atomic‐orbitals ground states for seven copper oxide crystals and Cu metal. The average net Mulliken charges calculated for Cu atoms in this way are shown to correlate well with the observed energies of the Cu K edge feature in x‐ray absorption spectra of these materials. Several of these compounds are important to understanding the high Tc superconductivity of copper oxides.

Photoionization mass spectrometry of NH2OH: Heats of formation of HNO+ and NOH+

Energy‐dependent mass spectra are presented for the most prominent ions produced upon photoionization of hydroxylamine. Two distinct thresholds are oberved for mass 31, which we attribute to onsets for formation of HNO+ and NOH+. The corresponding heats of formation are ΔH°f,0 (HNO+) = 256.8±1.4 kcal/mol and ΔH°f,0 (NOH+) = 274.8±0.7 kcal/mol. The thresholds for mass 32, which we tentatively ascribe to H2NO+, corresponds to 224.6±0.2 kcal/mol for its heat of formation. Each of these entities can therefore be produced in an exothermic reaction of H+3 with NO, and represent mechanisms for depleting NO in the interstellar clouds. Experimental breakdown diagrams are generated and compared with predictions of QET. It is found necessary to invoke a three‐body decomposition to explain some observations at higher energy. A theory is presented to accommodate this process within the framework of QET.

The fine and magnetic hyperfine structure of 87SrF in its X 2Σ+ state

A molecular beam rf–optical double resonance experiment was performed on 87SrF in its naturally occurring abundance ratio. The natural occurring abundances of the strontium isotopes are 86Sr (9.8%), 87Sr(7.02%) and 88Sr (82.5%). Numerous magnetic dipole allowed transitions between ρ‐doublets in the X 2Σ+ state were measured to an accuracy of 3 kHz. The observed spectra were analyzed in terms of an effective Hamiltonian which includes the magnetic hyperfine and electric quadrupole interactions arising from the 87 Sr (I=9/2) and 19F (I=1/2) nuclei. The extracted spectroscopic hyperfine parameters were interpreted in terms of a simple molecular orbital picture for the electronic nature of the X 2Σ+ state. A comparison is made to previous results for the more abundant 86SrF and 88SrF isotopic forms.

Hyperfine structure in the two lowest electronic states of PrO by molecular-beam laser-rf double resonance

The hyperfine structure (hfs) splittings in the electronic ground state ([Omega] = 3.5, [nu] = 0) and the first excited electronic level (Energy = 220 cm[sup [minus]1], [Omega] = 4.5, [nu] = 0) of [sup 141]PrO have been measured over a broad range of J-values to a precision of about [+-]3 kHz. No perturbations are observed. The levels are represented as states of Pr(III) 4[line integral][sup 2]6s in an axial electric field, and the hyperfine structure resulting from the combined hfs and rotational Hamiltonians is worked out. The contribution due to the interaction between the two states of different [Omega] is found to be important. A single least-squares fit is made of the resulting theoretical expressions to the 166 radiofrequency (rf) measurements in the two states. Efforts are made to identify the contributions analogous to the conventional terms involving b, c, and eqQ. The perturbations in the optical spectra (of systems XVII and of the band at 6,100 [angstrom]) are found to be in the common upper level (as previously reported), as is the [Lambda]-doubling. The hyperfine structure of the upper state is determined to a precision of a few Mhz.

Photoelectron spectra of Ga20, In20 and Tl20

Abstract The HeI photoelectron spectra of Ga2O, In2O, and Tl2O, as well as atomic In, have been obtained. Some spectral features of the recently published photoelectron spectrum of Al2O differ noticeably from the heavier suboxides. The assignment of spectral features is supported by fully relativistic DVM SSC Xα calculations, which have been extended to include Al2O. Best agreement is obtained between calculation and experiment for linear Al2O, but for bent heavier metal suboxides. In general, the spectral features are indicative of ionic bonding, analogous to the behavior of group IIIB monohalides. Along the sequence Al2O:Ga2O:In2O:Tl2O, the highest occupied orbital becomes less and less localized on the metal atoms, with a rather dramatic decrease in metal character occurring at Tl2O. The latter effect is attributable to a change in relative energies of the charge-adjusted metal and oxygen atomic orbitais and relativistic effects., A decrease in the relative ionization cross-section for molecular orbitais which have a large metal ns contribution is correlated with a similar behavior of the relative (ns)−1cross-section for the corresponding atoms.

PARTIAL CROSS SECTIONS IN THE PHOTOIONIZATION OF OPEN-SHELL ATOMS : PHOTOELECTRON SPECTROSCOPY OF TE

A general expression is derived for the relative partial cross sections for formation of fine structure states in the photoionization of open‐shell atoms. The expression is particularized to the cases of chalcogen and pnicogen atoms. By utilizing spectroscopic parameters, branching ratios from photoionization of the ground state, or other components of the lowest configuration, are predicted. New experimental data on atomic tellurium are reported, and compared with predicted branching ratios. The good agreement provides support for the calculational method, since this element is best characterized by intermediate coupling, and the intensities depart significantly from L–S based statistical weights. The comparative study of the pnicogen atoms is less revealing. Most of the intensity is concentrated in the triad 3P0,1,2, where experimental data suffer from limited resolution. A weak 1D2 peak is predicted for bismuth, where it has been observed, and for antimony, for which the relevant data are not yet avail...