The valence electronic excited states of trans-1,3-butadiene and trans,trans-1,3,5-hexatriene from generalized valence bond and configuration interact

Self-consistent ab initio generalized valence bond (GVB) and configuration interaction (Cl) calculations are presented for the ground and valence electronic excited states of trans-1,3-butadine and all trans-1,3,5-hexatrine. Previous workers have suggested that (all trans) polyenes exhibit a parity-forbidden valence excited state (2¹ A_g at an energy just below that of the first dipole-allowed (1¹ B_u) state. We find such valence excited electronic states for butadiene (ΔE = 7.06 eV) and hexatriene (ΔE = 5.87 eV), but in both cases the excitation energy is considerably higher than the dipole-allowed transitions (zero-zero transitions at 5.95 eV and 4.95 eV, respectively). The lower two triplet states are found at 3.35 eV and 5.08 eV for butadie and at 2.71 eV and 4.32 eV in hexatrine, in good agreement with experimental values (3.2–3.3 eV and 4.92 eV for butadiene and 2.66 eV and 4.1–4.2 eV for hexatrine). Considering the states formed by removing one electron from the π space we found ion states at 8.95 eV and 11.40 eV for butadiene and at 8.33 eV, 10.53 eV, and 11.60 eV for hexatriene, in godo agreement with experimental results (9.0 eV and 11.5 eV for butadiene and 8.45 eV, 10.43 eV and 11.6 eV for hexatriene).     

Low energy,variable angle electron-impact excitation of 1,3,5-hexatriene

A mixture of cis and trans 1,3,5-hexatriene has been studied by electron impact at incident electron energies of 20 eV, 40 eV, 50 eV, and 70 eV, at scattering angles from 0° to 80°, and with effective energy resolutions in the range from 0.05 eV to 0.15 eV. Singlet → triplet transitions with maximum intensities at 2.61 eV and 4.11 eV are observed. The lowest energy spin-allowed excitation which can be detected is the electric dipole-allowed $\text{X}$¹ A_g → 1 ¹B_u transition (in the notation appropriate for the trans isomer). No evidence has been found for a spin-allowed but symmetry-forbidden $\text{X}$¹ A_g → 2 ¹A_g excitation in the vicinity of 4.4 eV transition energy. Many other spin-allowed excitations are observed in the 6–11 eV energy-loss region, and the correlation between these features and those observed in high resolution ultraviolet absorption spectra and other electron-impact spectra is discussed.     

Photoelectron spectroscopy of radical anions

The photoelectron spectroscopy of a number of radical anions has been investigated. We find the following electron affinities: EA(C₃) =1.981 ±0.020 eV, EA(C₃H) = 1.858 ±0.023 eV, EA(C₃H₂) = 1.794 ± 0.025 eV, EA(C₃O) = 1.34±0.15 eV, EA(C₃O₂) = 0.85±0.15 eV, EA(C₄O)= 2.05±0.15 eV, and EA(CS₂) = 0.895± 0.020 eV. The structure and bonding for each of these ions is discussed.     

Graph-theoretical resonance energies of benzene and heterobenzenes from photoelectron spectra

Experimental values of π ionization potentials, non-subjective linear regression techniques, and graph theory are used to calculate resonance energies with the results, C₆H₆, 0.821 eV; C₆H₅N, 0.618 eV; C₆H₅P 0.661 eV; C₆H₅As, 0.545 eV; C₆H₅Sb, 0.607 eV.     

The valence shell spectra of acetylene and hydrogen excited by Zr Mζ x-rays. An example of the advantages provided by an ultra-soft x-ray source

Excitation of the valence shell molecular orbital spectrum of acetylene with Zr M_ζ (151.4 eV) radiation shows clearly all four expected bands 1π_u (11.4 eV), 3σ_g (16.8 eV), 2σ_u (18.8 eV) and 2σ_g (23.5 eV) with approximately equal intensity in contrast to He or Mg K_α excited spectra. A spectrum of molecular hydrogen can also be obtained with this radiation.     

The proton formation from methane by dissociative ionization in the electron energy range of 25–40 eV

The proton formation by dissociative electroionization of methane has been investigated in the energy range of 25–40 eV. The kinetic energy-versus-appearance energy shows five different H⁺ producing processes respectively at 26.3 ± 0.2 eV, 26.9 ± 0.2 eV, 29.4 ± 0.3 eV, 32.7 ± 0.2 eV and 35.7 ± 0.5 eV. These critical energies are discussed in terms of different dissociation channels probably opened through predissociation of doubly excited states of CH⁺₄. On the high energy side of the electron energy range investigated in the present work, the proton would appear through the dissociation of the CH⁺ ion as an intermediate.     

A quantum chemical study of gallium(III) (μ-oxo)bis[phthalocyaninate] and gallium(III) (μ-oxo)bis[perfluorophthalocyaninate] molecules

By the DFT (U)PBE0 method the structural parameters of molecules, cations, dications, and anions of gallium(III) (μ-oxo)bis[phthalocyaninate], gallium(III) (μ-oxo)bis[perfluorophthalocyaninate], and heteroleptic bis-phthalocyaninate ^FPcGaOGaPc are determined. The ∠GaOGa bond angle and the Ga?Ga internuclear distance depend non-monotonically on the charge. The ionization potential of the (PcGa)₂O molecule of 5.71 eV, the second electron detachment energy of 7.94 eV, and the electron affinity of 2.14 eV increase to 6.14 eV, 8.37 eV, and 2.72 eV after the perfluorination of one Pc moiety and to 6.60 eV, 8.70 eV, and 3.13 eV respectively after complete fluorination.     

Electron impact ionization of small silver and copper clusters

Using a quadrupole mass spectrometer, relative cross sections for electron impact ionization of neutral Ag _n and Cu _n clusters withn=1 ... 4 have been measured for electron energies between threshold and 125 eV. From the results, the following ionization energies were obtained: Ag₂: 7.26±0.1 eV, Ag₃: 6.19±0.2 eV, Ag₄: 6.33±0.3 eV, Cu₂: 7.46±0.15 eV, Cu₃: 6.14±1.0 eV, Cu₄: 7.00±0.6 eV. With only two exceptions, these values agree with other data published for Ag₂, Cu₂, Cu₃ and Cu₄.     

Total ionization and electron attachment cross sections of CCl2F2 by electron impact

The absolute total ionization cross sections from threshold to 250 eV and dissociative attachment cross sections from zero to 10 eV have been measured for the CCl₂F₂ (dichloro-difluoro-methane) molecule by using a parallel plate condenser type ionization chamber. The maximum of the ionization cross-section curve was found to be at an energy of about 90 eV with a cross section of 1.44 × 10^?19 m². The attachment cross-section curve shows three peaks, the most intense being at zero electron energy with a cross-section value of 1.80 × 10^?20 m², and the other two at energies of 0.6 eV and 3.5 eV, respectively. The maximal relative error in cross-section values is 0.08, for electron energies larger than 0.4 eV.     

Electron spectroscopy of hydrogen fluoride resonances

Transmission electron spectroscopy has been applied to determine the energies of resonances in HF. In addition to a sharp resonance at 10.05 eV, a resonance series exhibiting both vibrational and rotational structure is resolved in the energy range between 12 eV and 13 eV and the following molecular constants are obtained: B = 20.4 cm^?1, r_e, = 0.93 Å, ω_e 0.132 eV, ω_ex_e = 0.006 eV and D_e = 0.73 eV. The resonance spectrum is analysed with reference to an electron energy loss spectrum and approximate potential energy curves are deduced. Serious discrepancies are found between the present results and the data reported by Spence and Noguchi.     

The electronic spectrum of chloroformic acid in comparison to formic acid

The electronic spectra of chloroformic acid ClCOOH and formic acid HCOOH are computed in large-scale multireference configuration interaction (MRD-CI) calculations. The computed spectrum of formic acid is in reasonable agreement with prior calculations and experimental data. The first electronic transition of ClCOOH is computed at 6.41 eV (193.4 nm), about 0.5 eV higher than in HCOOH. Together with five strong transitions calculated at 7.66 eV (161.9 nm; 2(1)A' <-- X(1)A'), 8.36 eV (148.3 nm; 3(1)A' <-- X(1)A'), 8.49 eV (146.0 nm; 4(1)A' <-- X(1)A'), 9.00 eV (137.8 nm; 5(1)A' <-- X(1)A'), and 9.44 eV (131.3 nm; 7(1)A' <-- X(1)A'), this can serve as a guideline for experimental search of ClCOOH.     

VUV and photoelectronic spectra of methylstannane. Theoretical and experimental approach

The vacuum ultraviolet (VUV) and photoelectron spectra of SnH₃CH₃ were recorded between 6.20 and 11.28 eV and between 8 and 17 eV, respectively. Spectra were interpreted using ab initio CI calculations. The photoelectron spectrum confirmed the low SnC bond energy. The first two ionization potentials (IP) observed were attributed to the ionization of the a₁ (10.65 eV) and e orbitals (11.15 and 11.60 eV, split by the Jahn-Teller effect), thereby showing an inversion of IPs compared with ethane. Similarly, the first two bands of the VUV spectrum (at 7.04 and 7.72–8.16 eV) were attributed to a₁ and e transitions towards the Rydberg s orbital. A splitting of the same order of magnitude as that of the photoelectron spectrum could be noted in the E state. Observed transitions between 8.65 and 10 eV showed a strong interaction between the Rydberg p MO and the σ^*_SnC antibonding orbital. Primarilyvalence transitions were encountered beyond 10 eV.     

Formation of WF−6 and its dissociative products by collisional ionization

The formation of negative ions in electron transfer reactions between hyperthermal alkali atoms (Na, K) and WF₆ has been studied in the energy range 0–30 eV c.m. Relative cross sections and translational energy thresholds for ion pair formation have been measured, from which the following electron affinities (EA) and bond dissociation energies (D) have been derived: EA(WF₆) = 3.7 eV, EA(WF₅) = 1.25 eV, D(WF₅—F) = 5.1 eV, D)WF₅—F^?) = 5.4 eV, D(WF^?₅—F) = 7.6 eV. Several ion molecule reactions are discussed which result in formation of secondary fragmentation ions and WF^?₇.     

Excited electronic states of the fluorobenzenes by variable angle electron impact spectroscopy

Electron-impact excitation spectra of benzene, fluorobenzene, o-difluorobenzene, 1,3,5-trifluorobenzene, 1,2,3,4-tetrafluorobenzene, pentafluorobenzene, and hexafluorobenzene have been measured at impact energies of 50 eV and either 25 eV or 30 eV, and scattering angles from 5° to 80°. Each molecule shows an absorption maximum at about 3.9 eV corresponding to a singlet → triplet, π → π^*, transition. In benzene, fluorobenzene, o-difluorobenzene, and 1,3,5-trifluorobenzene, an additional singlet → triplet transition was detected at about 5.6 eV. Three singlet → singlet transitions analogous to the 4.90, 6.20, and 6.95 eV transitions in benzene are seen in each of the fluorine-substituted molecules. The more highly substituted compounds exhibit an additional singlet → singlet transition that is most clearly observed in the hexafluorobenzene spectrum with a peak at 5.32 eV.     

Gas-phase negative ions of platinum metal fluorides. II. Electron affinity of platinum metal hexafluorides

Reactions of platinum metal hexafluoride negative ions were studied by Knudsen cell mass spectrometry. The electron affinities were measured for OsF₆(5.93±0.28 eV), IrF₆ (6.50±0.38 eV), PtF₆(7.00±0.35 eV), and RuF₆ (6.47±0.31 eV).The relevant data on electron affinities of platinum metal hexafluorides are discussed.     

Single and Double Ionization of Corannulene and Coronene

Electron‐transfer processes that involve single and doubly charged cations of corannulene (C₂₀H₁₀) and coronene (C₂₄H₁₂) are examined by three different mass‐spectrometric techniques. Photoionization studies give first‐ionization energies of IE(C₂₀H₁₀)=7.83±0.02 eV and IE(C₂₄H₁₂)=7.21 ±0.02 eV. Photoionizations of the neutrals to the doubly charged cations occur at thresholds of 20.1±0.2 eV and 18.5±0.2 eV for corannulene and coronene, respectively. Energy‐resolved charge‐stripping mass spectrometry yields kinetic energy deficits of Q_min(C₂₀H=13.8±0.3 eV and Q_min(C₂₄H=12.8±0.3 eV for the transitions from the mono‐ to the corresponding dications in keV collisions. Reactivity studies of the C₂₀H and C₂₄H dications in a selected‐ion flow‐tube mass spectrometer are used to determine the onsets for the occurrence of single‐electron transfer from several neutral reagents to the dications, affording two different monocationic products. With decreasing IEs of the neutral reagents, electron transfer to doubly charged corannulene is first observed with hexafluorobenzene (IE=9.91 eV), while neutrals with lower IEs are required in the case of the coronene dication, e.g., NO₂ (IE=9.75 eV). Density‐functional theory is used to support the interpretation of the experimental data. The best estimates of the ionization energies evaluated are IE(C₂₀H₁₀)=7.83±0.02 eV and IE(C₂₄H₁₂)=7.21 ±0.02 eV for the neutral molecules, and IE(C₂₀H)=12.3±0.2 eV and IE(C₂₄H)=11.3±0.2 eV for the monocations.     

Energy levels of ionized states in a polydiacetylene crystal (PTS) studied by photoemission

Electron emission from partially and fully polymerized PTS single crystals has been measured upon excitation in the photon energy range 7 <hv < 11 eV. The ionization thresholds are 5.5 ± 0.1 eV for PTS polymer and 7.1 ± 0.1 eV for TS monomer. The bottom of the conduction band in PTS is located at A^P_C = ?3.1 ± 0.1 eV.     

Electronic energy states of certain sensitizers and dielectrics

Abstract— The electron affinities and ionization potentials of amorphous sulfur, vitreous selenium and several phthalocyanines were measured by Nelson's electron beam retardation method and photoelectric emission, respectively. The electron affinities (A_c) measured were: 4.5 eV for sulfur, 3.4eV for selenium, and approximately 4.3 eV for all the phthalocyanines measured. Photoemission thresholds (I_c) were 7.0 eV for sulfur and 6.0 eV for selenium. Two photoionization thresholds (at about 5.2 and 6.1 eV) were found for both α-copper and α-metal-free phthalocyanine; the former is attributed to impurity levels, the latter to bulk states. In each case, the band gap calculated from I_c and A_c was found to be approximately equal to the optical threshold for photoconductivity.     

Interface formation of Al2O3 on n‐GaN(0001): Photoelectron spectroscopy studies

Al₂O₃ insulator layers were deposited step by step by the physical vapor deposition (PVD) method onto gallium nitride in the wurtzite form, n‐type and (0001)‐oriented. The substrate surface and the early stages of Al₂O₃/n‐GaN(0001) interface formation were characterized in situ under ultra‐high vacuum conditions by X‐ray and ultraviolet photoelectron spectroscopy (XPS, UPS). The electron affinity (EA) of the substrate cleaned by annealing was 3.6 eV. Binding energies of the Al 2p (76.0 eV) and the O 1s (532.9 eV) confirmed the creation of the Al₂O₃ compound in the deposited film for which the EA was 1.6 eV. The Al₂O₃ film was found to be amorphous with a bandgap of 6.9 eV determined from the O 1s loss feature. As a result, the calculated Al₂O₃/n‐GaN(0001) valence band offset (VBO) is ?1.3 eV and the corresponding conduction band offset (CBO) 2.2 eV.     

(e,2e) Spectroscopy of methane

Measurements are reported on the spectroscopy of methane using the symmetric (e,2e) technique at energies of 600 eV and 1200 eV. The angular correlations of the states with separation energies of 14.2 and 23.1 eV have been measured and compared with the orbital wavefunctions of Snyder and Basch and with some earlier data at 400eV. The angular correlation of the configuration interaction state at 31 eV shows that this state definetely results from the removal of an electron in the 2a₁ orbital. Other structure at high separation energy is also identified with this orbital. Relative strengths of the It₂ and 2a₁ states are compared and found to be in agreement with the theory at 1200eV.