Configuration interaction calculations of satellite structure in photoelectron spectra of H2O

Configuration interaction wavefunctions were computed for the satellite peaks in the core and the valence photoelectron spectra of H₂O. Relative intensities were computed in the sudden approximation including electron correlation in the neutral ground state. The intensity profile of the O_1s ESCA spectrum is understood in terms of single excitations from the 3a₁ and the 1b₁ orbitals to low lying virtual MOs. Strong correlation effects are observed for the levels in the inner valence region where the satellites derive their intensity both from the 2a₁ and 3a₁ MOs.     

Vibrational spectra and normal coordinate analysis of germylazide-do and -d3

The infrared spectra (4000–20 cm^?1) of gaseous and solid GeH₃NNN and GeD₃NNN and the Raman spectra (3000–0 cm^?1) of liquid and solid GeH₃NNN and GeD₃NNN have been recorded. The vibrational spectrum has been assigned on the basis of C_s symmetry. The GeNN bend was observed in the Raman spectrum of the gas at ~150 cm^?1; however, the frequency of the GeH₃ torsion could not be determined. A normal coordinate calculation has been carried out by utilizing a modified valence force field. The GeN stretching force constant was found to have a significantly smaller value than the corresponding force constant in GeH₃NCO and GeH₃NCS. A considerable amount of mixing was found between the GeN stretch and the NNN in-plane bend. The frequencies of the normal modes and the normal coordinate analysis of GeH₃NNN are discussed in view of the recent results reported for GeH₃NCO and GeH₃NCS.     

All-valence-electron Cl calculations on the electronic spectrum of diborane

All-valence-electron Cl calculations have been carried out for diborane B₂H₆ and its positive ion employing a rather large double-zeta AO basis including polarization functions in order to study the electronic spectrum of this system. Transitions from four different valence MOs are found to lead to low-lying electronic transitions of both Rydberg and valence type in each case. Ad mixture of valence character in the otherwise Rydberg-like (nx, 3s), (ny, 3s) and (σ, 3pz) transitions calculated to lie between 11.0 and 11.6 eV is indicated as being primarily responsible for the highly intense shoulder found in this region of the B₂H₆ spectrum. The other strong feature with essentially continuous absorption peaking at 9.3 eV is suggested to result from superposition of several Rydberg-type transitions in the generally broad absorption pattern expected for the ¹(π,π^*) species at significantly higher vertical excitation energy. Quite good agreement is obtained between calculation and experiment for all of the six lowest IPs of diborane and also for the locations of the ¹(n, π^*) and ¹(σ, π^*) transitions previously assigned to the two weak features observed at 6.8 and 8.3 eV in this spectrum.     

SCF-Xα MO studies of the x-ray spectra of CuO and ZnO

SCF-Xα scattered wave cluster MO calculations for the oxyanions CuO^?6₄ (D_4h symmetry) and ZnO^?6₄ (Td symmetry) yield results in good agreement with the X-ray photoelectron and X-ray emission spectra of CuO and ZnO, respectively. Agreement of the calculations with optical data is fair. Calculations of the valence electron and core electron hole states of these oxyanions support the assignment of photoelectron shakeup satellites to valence band to conduction band transitions. Calculated shakeup energies for the Cu2p core spectrum in CuO are 7.4 and 9.9 eV (cf. experimental values of 7.5 and 10.0 eV) while shakeup peaks in the valence region spectrum are predicted at 6.1 and 8.0 eV. (Cf. a broad peak with maximum at 8.1 eV observed experimentally.) The absence of intense low energy satellites in the spectra of ZnO is explained by the small amount of electron reorganization in the outer valence levels attendant upon hole formation.     

Two-photon ionization spectrum of the 1Lb ← S0 transition in toluene

The multiphoton ionization (MPI) spectrum of toluene arising from the ¹B₂ (¹L_b) valence state has been investigated. The state participates as a two-photon resonance. A total of nine excited state fundamentals have been characterized, including three non-totally symmetric vibrations. The toluene MPI spectrum shows a strong resemblance to the two-photon fluorescence excitation spectrum with the strongest transitions taking place to the origin and excited state modes ν₁(a₁), ν₁₂(a₁) and ν₁₄(b)₂). The intensities of the observed fundamentals are rationalized in terms of Franck-Condon and vibronic coupling effects. A major conclusion is, that the primary mechanism for the activity of ν₁₂ is vibronic coupling.     

Electronic band structure of solid CO2 as determined from the hv-dependence of photoelectron emission

Photoelectron energy distribution curves from solid CO₂ have been determined for excitation energies from hv = 14 up to 40 eV using synchrotron radiation. A 1:1 correspondence to the gas-phase photoelectron spectrum is observed for the occupied molecular orbitals. The vertical binding energies E_B^v (E_VAC = 0) and widths (fwhm) of the valence bands of solid CO₂ are determined to be 13.0 and 0.95 eV (1π_g); 16.7 and 1.1 eV (1π_u); 17.6 and 0.85 eV (3σ_u) and 18.8 and 0.8 eV (4σ_g) for the individual bands respectively. The partial photoemission cross sections differ importantly from those of the gas phase in exhibiting pronounced maxima at 5.2 eV (1π_g), 4.4–5.3 eV (1π_u + 3σ_u) and 4.2 eV (4σ_g) above the vacuum level, which is attributed to effects of high density of final (conduction-band) states. Further weaker maxima are observed at higher photon energies. Contrary to the case for the gas phase, the resonances are unperturbed in the solid by degenerate autoionizing molecular Rydberg states. The molecular origin of the resonances in the continuum is discussed and related to X-ray absorption spectra, electron-scattering data and to theoretical cross-section calculations. It is shown that the same set of resonances is observed in the different experiments. The resonances occur however at different energies due to different Coulomb interactions. The photoemission results presented provide also a key to the hitherto unexplained optical spectrum of solid CO₂ in the VUV range, making possible an assignment of the structures observed to Frenkel-type excitons (hv ≤ 15 eV) and interband transitions (hv ? 15 eV).     

Shape resonances and partial photoemission cross sections of solid SF6 and CCl4

Photoelectron energy distribution curves from solid films of SF₆ and CCl₄ have been measured in the photon energy range 10 ? hr ? 40 eV using synchrotron radiation. The binding energies, peak widths and relative partial cross sections have been determined. In the photoelectron spectra a 1:1 correspondence to the gas phase is observed for the occupied molecular orbitals, and a straightforward assignment of the occupied valence bands emerges. Furthermore, the cross sections of the individual orbitals show for both samples great similarities to the gas phase. For SF₆ detailed structures are visible in the cross sections which are only partly interpreted as shape resonances. A new assignment for the 6t_1u shape resonance is proposed and the resonance energies are related to X-ray absorption and electron scattering data. Furthermore a comparison of the total photoemission cross section to the optical reflection spectrum of solid SF₆ is presented. For CCl₄ less structures are ob served in the partial cross sections. They are all interpreted as shape resonances. An energetic scheme of the virtual orbitals is proposed for CCl₄.     

The optical absorption spectra of small Silver clusters (n=8–39) embedded in rare gas matrices

The optical absorption of small mass selected Ag_n-clusters (n=8–39) embedded in solid Ar, Kr and Xe has been measured. Strong absorption has been found between 3 and 4.5 eV. The absorption spectra show 1 to 3 major peaks depending on the cluster size. The width of these peaks is smaller than in gas phase photodepletion experiments of silver ions, most likely due to the low and well defined temperature of the clusters in the matrix. The results are compared to a simple model based on a Drude metal, taking into account the spillout of the electrons and allowing for a deviation of the cluster from a spherical shape. Absorption cross sections scale with the number of valence electrons.     

On the excitonic nature of the first UV absorption peak in polyene

The first absorption peak in the UV spectrum of polyene is interpreted in terms of charge transfer excitons. The exciton spectrum has been calculated from first principles using the Green's function formalism of charge transfer exciton theory. Electron correlation effects on the polyene band structure have been included with the help of second order Møller-Plesset perturbation theory and of the electron polaron model of Toyozawa. The spectrum of bound singlet excitons starts at E_K=0 = 1.86 eV above the top of the valence band. A deeper lying triplet level is observed at 0.72 eV. Further correlation effects on the band gap and dielectric screening of the electron-hole ineraction are discussed.     

Mixed and partial oxidation states. Photoelectron spectroscopic evidence

X-ray photoelectron spectra of the single valence platinum complexes K₂[Pt(CN)₄] · 3H₂O(1),K₂[Pt(CN)₄]Cl_0.3 · n H₂O(2) and K₂[Pt(CN)₄]Cl₂ · 3H₂O(3) and the mixed valence compound [Pt^II(C₂H₅NH₂)₄]Cl₄ · [Pt^IV (C₂H₅NH₂)₄Cl₂] · 4H₂O(4) have been measured. It is found that one can distinguish clearly between mixed and single valence compounds by electron spectroscopy. The Pt spectrum of (4) is a superposition of a Pt^II and Pt_IV spectrum. The chemical shift between (1) and (3) is normal, however (2) shows an anomalous low binding energy for the Pt 4f electrons. The importance of using reliable reference peaks for obtaining absolute binding energies is emphasized.     

Structural and magnetic properties of double perovskite oxide Ba2CeSbO6

The structural and magnetic properties of a double perovskite oxide Ba₂CeSbO₆ (BCSO) synthesized by solid state reaction technique have been investigated. The Rietveld refinement of the X-ray diffraction pattern of BCSO suggests the monoclinic crystal structure at room temperature with P2₁/n space group. The vibrational properties of BCSO are investigated by the Fourier transform Infrared and Raman spectroscopy. The Raman spectrum confirms the B-site ordering of cations in BCSO. The temperature dependent magnetic susceptibility data in the field cooled mode show the anti-ferromagnetic behaviour of BCSO below 59 K. The core level X-ray photoemission (XPS) spectrum of Ce-3d and Sb-3d states confirms the presence of multiple oxidation states of these cations. The presence of both the Ce³⁺ and Ce⁴⁺ ions in BCSO gives the 4f^4−δ intermediate valence state which may reduce the effective magnetic moment with respect to the system having single valence Ce³⁺ ion.     

Spectra and structure of gallium compounds: Part VII. Microwave,infrared and raman spectra and normal coordinate analysis of trimethylamine-trimethylgallane

The infrared (100–3500 cm^?1) and Raman (25–3200 cm^?1) spectra of the solid phases of (CH₃)₃NGa(CH₃)₃ and (CH₃)₃¹⁵NGa(CH₃)₃ have been recorded near liquid nitrogen temperatures as well as the Raman spectrum (100–3200 cm^?1) of the liquid phase at ~50°C and the low resolution microwave spectrum (26.5–39.0 GHz) of (CH₃)₃NGa(CH₃)₃. The spectra have been interpreted on the basis of C_3v molecular symmetry and a vibrational assignment is proposed for all but the torsional modes. The B value calculated from the microwave spectrum is consistent with published structural parameters reported from an electron diffraction study. A modified valence force field has been used to calculate the observed frequencies and the potential energy distribution. The force constants presented are consistent with changes in the structural parameters of the Lewis acid and base upon adduct formation. Extensive mixing has been observed among the low-frequency modes. The Ga-N stretching force constant (1.6 mdyn A^?1) has a value intermediate between those of (CH₃)₃NGaH₃ and H₃NGa(CH₃₃).The lack of apparent factor group splitting indicates that only one molecule occupies each primitive cell, situated on either a C₃ or C_3v site. A rhombohedral space group such as R3m(C⁵_3v) is consistent with these observations.     

Untersuchungen an Stickstoff—Jod-Verbindungen. VII. Das IR-Spektrum des Stickstofftrijodid-1-Ammoniaks im Bereich der N–J-Grundschwingungen und Kraftkonstanten der N–J-Bindungen

Studies on nitrogen iodine compounds. VII. The IR spectrum of nitrogen triiodide-1 ammonia in the range of N—I fundamental vibrations and the valence force constants of the N—I bonds New infrared spectra in the region 33—600 cm^?1 of ¹⁴NI₃ · ¹⁴NH₃, ¹⁵NI₃ · ¹⁵NH₃ and ¹⁴NI₃ · pyridine, respectively, have been obtained. In addition, the infrared spectrum of ¹⁴NI₃ · ¹⁴ND₃, which has been prepared for the first time, was obtained. All absorption frequencies can be coordinated on the ground of the molecule model for the NI₃ scaffold with 5 atoms Z₂XY₂ of the symmetry C_2v which has been proved by X ray examination. A set of force constants has been calculated by approximation. The various nitrogeniodine valence force constants are discussed.     

The nature of the chemical bond in UO2

The nature of the chemical bond in UO₂ was analyzed taking into account the X-ray photoelectron spectroscopy (XPS) structure parameters of the valence and core electrons, as well as the relativistic discrete variation electronic structure calculation results for this oxide. The ionic/covalent nature of the chemical bond was determined for the UO₈ (D_4h) cluster, reflecting uranium's close environment in UO₂, and the U₁₃O₅₆ and U₆₃O₂₁₆ clusters, reflecting the bulk of solid uranium dioxide. The bar graph of the theoretical valence band (from 0 to ~35 eV) of XPS spectrum was built such that it was in satisfactory agreement with the experimental spectrum of a UO₂ single crystalline thin film. It was shown that unlike the crystal field theory results, the covalence effects in UO₂ are significant due to the strong overlap of the U 6p and U 5f atomic orbitals with the ligand orbitals, in addition to the U 6d atomic orbital (AO). A quantitative molecular orbital (MO) scheme for UO₂ was built. The contribution of the MO electrons to the chemical bond covalence component was evaluated on the basis of the bond population values. It was found that the electrons of inner valence molecular orbitals (IVMO) weaken the chemical bond formed by the electrons of outer valence molecular orbitals (OVMO) by 32% in UO₈ and by 25% in U₆₃O₂₁₆.     

Ab initio valence bond calculations. VII. HF,HF+, and H2F+

Ab initio valence bond calculations for the ground and excited states of HF and HF⁺ are presented. Total energies, equilibrium geometries, dissociation energies, dipole moments, and spectroscopic constants for HF and HF⁺ have been calculated. The photoelectron spectrum of HF has been examined and interpreted by means of the valence bond formalism. The ground state of the protonated species H₂F⁺ has been investigated.     

Direct observation of rotational states of molecular ions in photoionization processes

Optical transitions from H₂ (X ¹Σ_g⁺) to specific vibration-rotation states of the hydrogen molecular ion (X ²Σ_g⁺) have been directly observed and the spectrum is herein reported. A new method of zero kinetic energy electron analysis has been employed for the detection of the specific states and non-threshold electron peaks are not observed. It is shown that auto-ionization processes that produce threshold electrons will reveal ionic states that otherwise are not detectable.     

Vibrational spectrum of CO2− in an argon matrix

Absorptions which appear near 1600 cm^?1 on co-deposition at 14 K of Ar:CO₂ mixtures with an alkali metal have been assigned to ν₃ of an M⁺...CO₂^? ion pair, with an OCO valence angle near 130°. Molecular aggregates contribute significantly to the observed spectrum.     

Infrared and Raman spectra, ab initio calculations and vibrational assignment for 3-fluoro-1-butyne

The infrared (3500-80 cm⁻¹) and Raman (3500-20 cm⁻¹) spectra of 3-fluoro-1-butyne, CH₃CHFCCH, have been recorded for the gas and solid. Additionally, the Raman spectrum of the liquid has also been recorded to aid in the vibrational assignment. Ab initio electronic structure calculations of energies, geometrical structures, vibrational frequencies, infrared intensities, Raman activities and the potential energy function for the methyl torsion have been calculated to assist in the interpretation of the spectra. The fundamental torsional mode is observed at 251 cm⁻¹ with a series of sequence peaks falling to lower frequency. The three-fold methyl torsional barrier is calculated to be 1441 ± 20 cm⁻¹ (4.12 ± 0.06 kcal mol⁻¹) where the uncertainty is partly due to the uncertainty in values of the V₆ term. A complete vibrational assignment is proposed based on band contours, relative intensities, and ab initio predicted frequencies. Several fundamentals are significantly shifted in the condensed phases compared to values in the vapor state.     

Cationic Rydberg states observed in resonantly enhanced electron spectra of CS2

The inner valence electron spectrum of the CS₂ molecule has been investigated in the binding energy range between 18.6 and 26.3 eV using synchrotron radiation for ionisation. Photon energies in the range from 67 to about 167 eV have been used, with particular focus on 166.70, 166.89 and 167.09 eV for which S2p electrons are resonantly transferred into Rydberg orbitals close to the ionisation threshold. From there, autoionisation takes the molecule into various cationic states characterized by two valence holes and a Rydberg spectator electron. Many new bands are observed which contain vibrational progressions with spacings around 120 meV in most cases. These are assigned as excitations of the totally symmetric stretching ν₁ mode in the cationic state. The new bands reflect states in the cation that are close to the electronic states of the dication and assignments are made by comparison to double ionisation electron spectra.     

Conformational analysis,barriers to internal rotation and vibrational assignment for dimethylethylamine

The IR (50–3500 cm^?1) and Raman (20–3500 cm^?1) spectra have been recorded for gaseous and solid dimethylethylamine. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values have been obtained. Due to the fact that three distinct Raman lines disappear on going from the fluid phases to the solid state, it is concluded that the molecule exists as a mixture of the gauche and trans conformers in the fluid phases with the gauche conformer being more stable and the only one present in the spectra of the unannealed solid. From the temperature study of the Raman spectrum of the liquid a rough estimate of 3.9 kcal mol^?1 has been obtained for ΔH. Relying mainly on group frequencies and relative intensities of the IR and Raman lines, a complete vibrational assignment is proposed for the gauche conformer. The potential functions for the three methyl rotors have been obtained, and the barriers to internal rotation for the two CH₃ rotors attached to the nitrogen atom have been calculated to be 3.51 and 3.43 kcal mol^?1, whereas the barrier for the CH₃ rotor of the ethyl group has been calculated to be 3.71 kcal mol^?1. The asymmetric torsional mode for the gauche conformer has been observed in both the IR and Raman spectra of the gas at 105 cm^?1 with at least one hot band at a lower frequency. Since the corresponding mode has not been observed for the trans conformer, it is not possible to obtain the potential function for the asymmetric rotation although estimates on the magnitudes of some of the terms have been made. Significant changes occur in the low-frequency IR and Raman spectra of the solid with repeated annealing; several possible reasons for these changes are discussed and one possible explanation is that a conformational change is taking place in the solid where the trans form is stabilized by crystal packing forces. These results are compared to the corresponding quantities for some similar amines.