D. A. Shirley

Paramagnetic Resonance of Fe3+ in Polycrystalline Ferrichrome A

Polycrystalline samples of iron‐containing ferrichrome A, a cyclic hexapeptide obtained from the fungus Ustillago sphaerogena, have been investigated by paramagnetic resonance. Spectra were obtained at several temperatures between 300° and 1°K; a prominent line of 400‐Oe width located at g=4.3 was observed at all temperatures, while at 1°K additional resonances at g values of 9.6, 1.3, and 1.0 were observed. The spectra are interpreted by assuming a spin Hamiltonian containing crystal‐field terms large compared with the Zeeman splittings; the crystal‐field situation is intermediate between the case of axial symmetry, with H=D[Sz2−(1/3)S(S+1)]+gβS·H and a model proposed by Castner, Newell, Holton, and Slichter to explain certain iron resonances occurring at g=4.3, with H=E(Sx2−Sy2)+gβS·H. We have computed g values, energy eigenvalues, and eigenfunctions to be expected for the region between these two extremes, and the results should be useful in interpreting similar spectra due to iron situated in strong c...

The effect of atomic and extra-atomic relaxation on atomic binding energies☆

Abstract An equivalent-cores-relaxation model is given for calculating atomic binding energies from orbital energies using only ground-state atomic properties. The agreement with experiment is excellent for the noble gases. On the basis of present knowledge of atomic relaxation, the phenomenon of “extra-atomic relaxation”, in which electronic charge is attracted toward a hole-state atom, is shown to have an important effect in lowering atomic core-level binding energies in condensed phases. This will affect the interpretation of most core-level binding energies measured to date.

The electronic structure of SrTiO3 and some simple related oxides (MgO, Al2O3, SrO, TiO2)☆

Abstract The valence band density of states (VBDOS) of the insulating oxides SrTiO 3 , TiO 2 , SrO, MgO and Al 2 O 3 obtained by X-ray photoelectron spectroscopy (XPS), are reported. Qualitatively, the VBDOS of these oxides are similar to one another. The XPS results are compared with results from soft X-ray emission spectroscopy (XES), ultraviolet photoemission spectroscopy (UPS), and theoretical calculations. There are some differences (in particular for TiO 2 ) between the XES and XPS results, which are probably due to matrix element effects enhancing different features of the VBDOS in the two techniques. The XPS results definitively establish the position of the O 2 s level, which had been erroneously assigned in previous low-energy UPS measurements. Cluster-type calculations are demonstrated to give a reasonable representation of the VBDOS for the oxides.

CHEMICAL EFFECTS ON CORE ELECTRON BINDING ENERGIES IN IODINE AND EUROPIUM

A theoretical and experimental study was made of the shift in atomic core‐electron binding energies caused by the chemical environment. Two models are presented to account for these “chemical shifts.” The first uses an energy cycle to break the core‐electron binding energies into a free‐ion contribution and a classical Madelung energy contribution. The Madelung energy contributes a significant part of the binding‐energy shift. It can, in principle, be evaluated rigorously although there is some ambiguity as to a surface correction. The reference level for binding energies must also be considered in comparing theory with experiment (or in comparing experimental shifts with one another). Electronic relaxation could also introduce errors of ∼1 eV in shift measurements. The second, more approximate, model consists of a “charged‐shell” approximation for bonding electrons in atomic complexes. It gives semiquantitative estimates of shifts and demonstrates the relationship between bond polarity and core‐electron ...

Nuclear quadrupole interaction studies by perturbed angular correlations

A comperhensive study was made of the applicability of gamma‐ray angular correlations to the determination of quadrupole interactions in metals and insulating solids. Dynamic effects were studied in solutions and gases. A total of fourteen gamma‐ray cascades were employed. Several nuclear spins were confirmed and the quadrupole moments of ten excited nuclear states were determined or estimated from the data. Quadrupole coupling constants were determined for excited states of the following nuclei in metallic host lattices of the same element: 44Sc, 99Ru, 111Cd, 117In, 187Re, 199Hg. Coupling constants were also measured for the following isotope (lattice) combinations: 99Ru(Zn, Cd, Sn, Sb), 100Rh(Zn, Ru, Cu5Zn8, Pd2Al, PdPb2), 111Cd(In, Hg, Tl, CdSb, Cd3Ag, Zn, Ga, In, Sn, Sb, Bi, AuIn, InBi, In2Bi), 115In(Cd), 117In(Cd, Sn), 131I(Te), 181Ta(HfB2, HfSi2), 204Pb(Cd, In, Sn, As, Sb, Bi, Hg, Tl, PdPb2). Systematic variations of e2qQ with host‐lattice structure were observed and host and solute properties were ...

Theory of core‐level photoemission correlation state spectra

A theoretical framework is given for calculating satellite spectra (sometimes called ’’shakeup’’ or ’’monopole’’ spectra) that accompany core‐level photoemission peaks. Photoemission is regarded as a special case of optical excitation in an N‐electron system, and the dipole approximation (DA) is used to determine satellite intensities. relationships between the sudden approximation and DA results are noted. Configuration interaction (CI) in the final state is discussed. It is emphasized that the main core‐level peak and satellites do not really arise from one‐ and two‐electron excitations, respectively, but from qualitatively identical transitions. The importance of initial‐state CI in determining satellite intensities in molecular x‐ray photoelectron spectra is pointed out for the first time.

Molecular beam photoelectron spectroscopy and femtosecond intramolecular dynamics of H2O+ and D2O+

The 584 A photoelectron spectra of supersonic molecular beams of H2O and D2O have been obtained with improved resolution. The spectroscopic constants of the X 2B1 and A 2A1 state ions, including ω01, x011, ω02, x022, and x012, are reported. For the first two electronic states of the ion, precise line splittings were evaluated with a least squares fitting procedure, employing sums of empirical instrument response functions and a linear background. A simulation of the vibrational manifolds of the B 2B2 state ions with combination progressions in the symmetry‐allowed modes ν1 and ν2 failed to reproduce the diffuse photoelectron bands observed for both H2O and D2O. Autocorrelation functions were calculated from the photoelectron bands of all three electronic states. The B 2B2 state correlation functions exhibit ultrafast decay, occurring on a 10−14 s time scale. The ν2 motion appears to define the decay in the correlation function. This behavior supports a previously proposed B 2B2–A 2A1 curve‐crossing ...

High resolution UV photoelectron spectroscopy of CO+2, COS+ and CS+2 using supersonic molecular beams

Abstract Very high resolution HeI (584 A) photoelectron spectra of CO+2, COS+, and CS+2 are presented. The spectra were obtained by using supersonic molecular beams to eliminate the rotational and Doppler broadenings. The spin-orbit split components in the Π bands are all explicitly resolved. The removal of the inelastic scattering peaks, due to the use of molecular beams, allowed new features to be observed in the B and C bands of CS+2, and new spectroscopic constants were derived.

A relaxation correction to core-level binding-energy shifts in small molecules☆

Abstract A theoretical method for correcting core-level binding-energy shifts for final-state relaxation effects in the framework of the CNDO model is derived a binding energies in gaseous molecules.

Photoelectron spectroscopy and inferred femtosecond intramolecular dynamics of C2H+2 and C2D+2

The 584 A photoelectron spectra of rotationally cold C2H2 and C2D2 were obtained with improved resolution, permitting the first three electronic states of the ions to be characterized in greater detail. Temperature‐dependent studies led to a definitive assignment of the low intensity features in the X 2∏u state, yielding ν4=837±12 cm−1 for C2H+2 and ν4=702±12 cm−1 for C2D+2. The ν5 origin of the Renner–Teller multiplet was identified. In the case of C2D+2, a Fermi resonance with this multiplet contributed intensity to the ν1 mode, facilitating its evaluation at 2572±16 cm−1. The C2h geometry of the A 2Ag state was determined from the two previously unobserved bending progressions, assigned to ν4 and ν5B, and evaluated at 492±12 and 605±12 cm−1 for C2H+2 and 339±12 and 516±12 cm−1 for C2D+2, respectively. A more extensive vibrational progression than previously evident, comprised of irregular spectral features indicative of nonadiabatic effects, was observed for the B 2∑+u state. Autocorrelation function...