ChemInform Abstract: Theoretical Study on Electronic Structures of AuF6 and Its Anions.

SCF-MO and CI calculations on AuFn6^- (n = 0-3) (model potential method) show that the AuF₆^- anion has the lowest minimum energy in this series and the energy of the AuF₆^3- anion is ∼ 4 eV higher than that of AuF₆^- and AuF₆^2- at their equilibrium positions.     

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.     

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.     

Magnetic-Bottle and Velocity-Map Imaging Photoelectron Spectroscopy of APS- (A=C14H10 or Anthracene): Electron Structure,Spin-Orbit Coupling of APS·, and Dipole-Bound State of APS-

Gaseous dibenzo-7-phosphanorbornadiene P-sulfide anions APS^-(A=C₁₄H₁₀ or anthracene) were generated via electrospray ionization, and characterized by magnetic-bottle photoelectron spectroscopy, velocity-map imaging (VMI) photoelectron spectroscopy, and quantum chemical calculations. The electron affinity (EA) and spin-orbit (SO) splitting of the APS^· radical are determined from the photoelectron spectra and Franck-Condon factor simulations to be EA=(2.62±0.05) eV and SO splitting=(43±7) meV. VMI photoelectron images show strong and sharp peaks near the detachment threshold with an identical electron kinetic energy (eKE) of 17.9 meV at three different detachment wavelengths, which are therefore assigned to autodetachment from dipole-bound anion states. The B3LYP/6-31++G(d, p) calculations indicate APS^· has a dipole moment of 3.31 Debye, large enough to support a dipole-bound electron.     

Fullerene “Superhalogen” Radicals: the Substituent Effect on Electronic Properties of 1,7,11,24,27‐C60X5

Hexasubstituted fullerenes with the skew pentagonal pyramid (SPP) addition pattern are predominantly formed in many types of reactions and represent important and versatile building blocks for supramolecular chemistry, biomedical and optoelectronic applications. Regioselective synthesis and characterization of the new SPP derivative, C₆₀(CF₃)₄(CN)H, in this work led to the experimental identification of the new family of “superhalogen fullerene radicals”, species with the gas‐phase electron affinity higher than that of the most electronegative halogens, F and Cl. Low‐temperature photoelectron spectroscopy and DFT studies of different C₆₀X₅ radicals reveal a profound effect of X groups on their electron affinities (EA), which vary from 2.76 eV (X=CH₃) to 4.47 eV (X=CN). The measured gas‐phase EA of the newly synthesized C₆₀(CF₃)₄CN equals 4.28 (1) eV, which is about 1 eV higher than the EA of Cl atom. An observed remarkable stability of C₆₀(CF₃)₄CN^? in solution under ambient conditions opens new venues for design of air‐stable molecular complexes and salts for supramolecular structures of electroactive functional materials.     

Thermal energy rate constants for the reactions NO2 + Cl2 → Cl2 + NO2, Cl2 + NO2 → Cl + NO2Cl,SH + NO2 → NO2 + SH,SH + Cl2 → Cl2 + SH,and S + NO2 → NO2 + S

It is found that charge-transfer on NO⁻₂ with Cl₂ is fast at thermal energy. The Cl⁻₂ ion reacts with NO₂ to produce Cl⁻ and NO₂Cl, and SH⁻ charge-transfers rapidly with both Cl₂ and NO₂. From the exothermicities implied it is deduced that EA (SH)<EA (NO₂)< EA (Cl₂) or EA (NO₂) = 2.38 ± 0.06 eV and EA (Cl₂ = 2.46 ± 0.14 eV.     

Electron affinities of higher molybdenum fluorides as determined by the effusion technique

The effusion technique with mass spectral recording of ions was employed to investigate the ionic component of molybdenum trifluoride saturated vapour. The equilibrium constants of ion—molecular reactions involving MoF₅^?, MoF₆^? and MoOF₄^? were measured. The following thermodynamic values were obtained from experimental data: MoF₄(g) + F^?(g) = MoF₅^?(g),ΔH₂₉₈⁰ = ?382.0 ± 20.1 kJ/mole; MoF₅(g) + F^?(g) = MoF₆^?(g), ΔH₂₉₈⁰ = ?413.4 ± 20.1 kJ/mole; MoOF₃(g) + F^?(g) = MoOF₄^?, ΔH₂₉₈⁰ = ?418.0 ± 20.5 kJ/mole; EA(MoF₅ = 3.6 ± 0.2 eV, EA(MoF₆) = 3.6 ± 0.2 eV, EA(MoOF₄) = 4.0 ± 0.4 eV. Reported as well as estimated molecular constants were used to calculate thermodynamic functions of some participants of ion—molecular reactions. For MoOF₃, BeF₃^? and Be₂F₅^? vibration frequencies were calculated from the estimated force field.     

Photodissociative formation of ion pairs from molecular hydrogen and the electron affinity of the hydrogen atom

Photodissociative production of ion pairs from H₂ has been observed in the wavelength range 706–718 A at spectral resolution of 0.4 and 0.22 A. From measured thresholds for production of H^? from H₂ molecules in each of the three lowest rotational states, the lower bound EA(H) ? 0.754 ± 0.002 eV is obtained, in excellent agreement with the theoretical electron affinity of 0.75421 eV. For formation of D^? from D₂, a threshold assigned to molecules in the rotational state J = 2 has been measured, from which the bound EA(D) ? 0.757 ± 0.005 eV is obtained. Negative ion yield curves are presented for hydrogen.     

Observation of X1A1 vinylidene by photoelectron spectroscopy of the C2H2− ion

Photoelectron spectra of the vinylidene anion (C₂H₂^?) show vibrational structure in X¹A₁ vinylidene up 12 kcal/ mol above the vibrational ground state. Analysis yields an EA(C₂H₂$\text{X}$¹ A₁) of 0.47 ± 0.02 eV, and frequencies for the CC stretch and HCH bend. Absence of the ³B₂ state in the photoelectron spectra indicates the ¹A₁-³B₂ splitting in vinylidene is ? 1.7 eV.     

Infrared photodetachment measurements near thresholds of C−

The relative cross section has been measured in the threshold regions of the following transitions: C^?(⁴S) + hv → C³P_0,1,2) + e^? and C^?(²D) + hv → C(¹D) + e^?. The electron affinity of carbon is determined EA(C) = 1.2629 ± = 0.0003 eV, and the binding energy of the metastable C^?(²D) state with respect to the C(³P₀) ground state is 0.033 ± 0.001 eV.     

Absolute rate constants for the addition of hydroxymethyl radicals to alkenes in methanol solution

Absolute rate constants and their temperature dependencies were determined for the addition of hydroxymethyl radicals (CH₂OH) to 20 mono- or 1,1-disubstituted alkenes (CH₂ = CXY) in methanol by time-resolved electron spin resonance spectroscopy. With the alkene substituents the rate constants at 298 K (k₂₉₈) vary from 180 M^?1s^?1 (ethyl vinylether) to 2.1 middot; 10⁶ M^?1s^?1 (acrolein). The frequency factors obey log A/M^?1s^?1 = 8.1 ± 0.1, whereas the activation energies (E_a) range from 11.6 kJ/mol (methacrylonitrile) to 35.7 kJ/mol (ethyl vinylether). As shown by good correlations with the alkene electron affinities (EA), log k₂₉₈/M^?1s^?1 = 5.57 + 1.53 · EA/eV (R² = 0.820) and E_a = 15.86 ? 7.38 · EA/eV (R² = 0.773), hydroxymethyl is a nucleophilic radical, and its addition rates are strongly influenced by polar effects. No apparent correlation was found between E_a or log k₂₉₈ with the overall reaction enthalpy. © 1995 John Wiley & Sons, Inc.     

High Compression-Induced Conductivity in a Layered Cu–Br Perovskite

We show that the onset pressure for appreciable conductivity in layered copper-halide perovskites can decrease by ca. 50 GPa upon replacement of Cl with Br. Layered Cu–Cl perovskites require pressures >50 GPa to show a conductivity of 10⁻⁴ S cm⁻¹, whereas here a Cu–Br congener, (EA)₂CuBr₄ (EA=ethylammonium), exhibits conductivity as high as 2×10⁻³ S cm⁻¹ at only 2.6 GPa, and 0.17 S cm⁻¹ at 59 GPa. Substitution of higher-energy Br 4p for Cl 3p orbitals lowers the charge-transfer band gap of the perovskite by 0.9 eV. This 1.7 eV band gap decreases to 0.3 eV at 65 GPa. High-pressure X-ray diffraction, optical absorption, and transport measurements, and density functional theory calculations allow us to track compression-induced structural and electronic changes. The notable enhancement of the Br perovskite's electronic response to pressure may be attributed to more diffuse Br valence orbitals relative to Cl orbitals. This work brings the compression-induced conductivity of Cu-halide perovskites to more technologically accessible pressures.     

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.     

High Compression‐Induced Conductivity in a Layered Cu–Br Perovskite

We show that the onset pressure for appreciable conductivity in layered copper‐halide perovskites can decrease by ca. 50 GPa upon replacement of Cl with Br. Layered Cu–Cl perovskites require pressures >50 GPa to show a conductivity of 10^?4 S cm^?1, whereas here a Cu–Br congener, (EA)₂CuBr₄ (EA=ethylammonium), exhibits conductivity as high as 2×10^?3 S cm^?1 at only 2.6 GPa, and 0.17 S cm^?1 at 59 GPa. Substitution of higher‐energy Br 4p for Cl 3p orbitals lowers the charge‐transfer band gap of the perovskite by 0.9 eV. This 1.7 eV band gap decreases to 0.3 eV at 65 GPa. High‐pressure X‐ray diffraction, optical absorption, and transport measurements, and density functional theory calculations allow us to track compression‐induced structural and electronic changes. The notable enhancement of the Br perovskite's electronic response to pressure may be attributed to more diffuse Br valence orbitals relative to Cl orbitals. This work brings the compression‐induced conductivity of Cu‐halide perovskites to more technologically accessible pressures.     

Vacuum ultraviolet photoelectron spectroscopy of transient species. XVII. The SiH3(X 2A1) radical

The first band in the vacuum ultraviolet photoelectron spectrum of the silyl radical, corresponding to the process SiH₃ (X ¹A′₁) ← SiH₃(X ²A₁), has been observed with HeI radiation. Extensive vibrational fine structure associated with the SiH₃⁺ deformation vibration was observed in this band and analysis of the structure gave a value of ω = 820 = 40 cm^-1 for the out-of-plane deformation mode in the ion. The vertical and adiabatic ionization energies were measured as 8.74 = 0.01 eV and 8.14 ± 0.01 eV respectively and use of the latter value together with the established heat of formation of the silyl radical allows an improved heat of formation of SiH₃^-. ΔH₂₉₈⁰ (SiH₃^-) to be derived as 980 ± 7 kJ mol^?1.     

Measurement of Electron Affinity of Atomic Lutetium via the Cryo-SEVI Method

Electron affinities (EAs) of most lanthanide elements still remain unknown due to their relatively low EA values. In the present work, the cryogenically controlled ion trap is used for accumulating atomic lutetium anion Lu^-, which makes the measurement of electron affinity of lutetium become practicable. The high-resolution photoelectron spectra of Lu^- are obtained via the slow-electron velocity-map imaging method. The electron affinity of Lu is determined to be 1926.2(50) cm^-1 or 0.23882(62) eV. In addition, two excited states of Lu^- are observed.     

Ion-Pair Photodissociation of Trichloromonofluoromethane

Anionic fragments, F^- and Cl^- including two isotope species ³⁵Cl^- and ³⁷Cl^-, are ob-served in the photoexcitations of CFCl₃. The ion-pair anion e±ciency spectra of ³⁵Cl^- and ³⁷Cl^- are recorded in the photon energy range of 7.75～22.00 eV. The threshold of ion-pair dissociation CFCl₃→CFCl₂⁺+Cl^- is experimentally determined to be 7.94±0.04 eV. With the references of the high-resolution photoabsorption spectra reported in the literatures, we make tentative assignments of the electron valence-to-Rydberg transitions. Furthermore, the multibody ion-pair fragmentation processes to Cl^- are discussed by comparison between the calculated thermochemical thresholds and the experimental efficiency spectrum.     

Structure and stability for (AlN) n + and (AlN) n + (n=1–15) clusters

Using density functional theory (DFT) method with 6-31G* basis set, we have carried out the optimizing calculation of geometry, vibrational frequency and thermodynamical stability for (AlN) _n ⁺ and (AlN) _n ⁺ (n=1–15) clusters. Moreover, their ionic potential (IP) and electron affinity (EA) were discussed. The results show that the electrical charge condition of the cluster has a relatively great impact on the structure of the cluster and with the increase of n, this kind of impact is reduced gradually. There are no Al-Al and N-N bonds in the stable structure of (AlN) _n ⁺ or (AlN) _n ^-, and the Al-N bond is the sole bond type. The magic number regularity of (AlN) _n ⁺ and (AlN) _n ^- is consistent with that for (AlN) _n , indicating that the structure with even n such as 2, 4, 6, ... is more stable. In addition, (AlN₁₀ has the maximal ionization power (9.14 eV) and the minimal electron affinity energy (0.19 eV), which manifests that (AlN)₁₀ is more stable than other clusters.     

‘Non-Koopmans’ States in Stilbene Cations and a Remarkable Example to the «SDT-Equation»: Indeno [2,1-a]indene

The radical cations of indeno [2, 1-a]indene ( 1 ), stilbene ( 2 ) and 3, 5, 3', 5'-tetramethylstilbene ( 3 ) were prepared by γ-irradiation of the neutral precursors in an electron-scavenging matrix at 77 K . Their electronic spectra were recorded and compared to the photoelectron spectra ( PE .) of the neutral precursors. The results show that either the fourth or the fifth excited doublet state of the cations is of «Non-Koopmans» type, with specific doublet energy (D) D (²B_g)=2.74 eV ( 1 ⁺), =2.59 eV ( 2 ⁺), =2.49 eV ( 3 ⁺). Remarkably, 1 ⁺ possesses two electronic states in the 2.7-2.8 eV energy range: ²A_u («Koopmans»-type) and ²B_g («Non -Koopmans»-type). The «SDT»-equation \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm D} = \sqrt {{\rm S} \cdot {\rm T}} $\end{document} approximately connecting excited singlet (S) and triplet (T) states of a neutral alternant system with the excited doublet (D) states of its radical cation - provided e-promotion occurs For all three excited states between the same (paired) orbitals-is satisfyingly exemplified by 1 : S¹ = 3.92 eV and T¹= 2.06 eV for 1 , D^{4 or 5}=2.74 eV for 1 ⁺.     

Radiative decay of vibrationally excited CH2-

We have observed the presence of vibrationally excited CH₂^- created in a discharge, by measuring the photodetachment from CH₂^- as it radiatively relaxes in a high vacuum ion trap. We used a tunable IR laser to produce photons with energies above and below the expected threshold for removing an electron from the ground state. The time dependence of the photodetachment is consistent with the electron affinity of 5250 cm^-1 (0.65 eV) obtained by Sears and Bunker for the ground state X?³B₁ methylene. We have tentatively assigned radiative lifetimes for the excited bending vibrations of CH₂^-:600 ±300 msec for v₂ = 1,80±40msec for v₂ = 2, and 10± 5 msec for v₂ = 3.