Resonant scattering of slow electrons from naphthalene vapour

Resonant scattering of low energy electrons from naphthalene has been investigated using electron transmission spectroscopy. The transmission spectrum of naphthalene yields a value of ?0.20 ± 0.05 eV for the first electron affinity. The first and second excited states of C₁₀H^?₈ are detected at 0.96 ± 0.1 eV and 1.55 ± 0.13 eV. Resonant structure is also observed at 5.29 ± 0.1 cV and 7.55 ± 0.05 eV; it is suggested that the former resonance is the previously unidentified peak in the threshold electron excitation spectrum of Compton and co-workers.     

Dissociation energy and ionization potential of the molecule CF

The gaseous equilibrium S + CF₂ = SF + CF was studied over the temperature range 1851 to 2232 K by mass spectrometry, and the derived enthalpy change was used to evaluate the heat of formation of CF ΔH₂₉₈ = 58.0 ± 2.4 kcal/mol (2.52 ± 0.10 eV), and the dissociation energy D₀⁰ (CF) = 130.8 ± 2.4 kcal/mol (5.67 ± 0.10 eV). The new thermochemical data indicate a slightly higher stability for CF than earlier determinations. Direct measurement by electron impact yielded a value of 9.17 ± 0.10 eV for the vertical ionization potential of CF, in agreement with an indirect result obtained from the photodissociative ionization of C₂F₄.     

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.     

Absolute photo-emission cross section of the BClA 1Π →X 1Σ+ system produced by dissociative electron impact on BCl3

We measured the absolute photo-emission cross section of the BC ? A → X system around 2720 Å produced by electron-impact dissociation of BC?₃. The cross section reaches a maximum around 40 eV with a value of 2.5±0.5 × 10^?18 cm². A double-onset structure with onsets around 14 eV and 26 eV indicates that the excited BC? fragments are produced via two different dissociation channels.     

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.     

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.     

Photoemission from solid neon

The photoelectric yield of solid Ne has been studied for photon energies between 15 and 30 eV. Strong photoemission from the valence band sets in at 21.4 ± 0.1 eV. The value of the electron affinity derived from this is discussed. A surface resonance for Ne atoms adsorbed on gold is observed at 17.1 eV.     

Electron inity of 1,3,5,7-cyclooctatetraene determined by the kinetic method

The kinetic method is used to determine the electron inity (EA) of 1,3,5,7-cyclooctatetraene (COT), a compound that undergoes a significant structural change upon electron attachment. Collision-induced dissociation of anionic clusters of COT with a set of reference compounds (Ref), [COT·Ref]^?·, at various collision energies, allowed deconvolution of the relative enthalpies and entropies of the competitive reactions. The adiabatic EA of COT is determined to be 0.58±0.10 eV, in good agreement with the value, 0.58±0.04 eV, of Wentworth and Ristau (J. Phys. Chem. 1969, 73, 2126) determined by thermal electron detachment as well as the more recent value, 0.55±0.02 eV, of Kato et al. (J. Am. Chem. Soc. 1997, 119, 7863) determined by equilibrium electron transfer with molecular oxygen. A large entropy difference, 25.6±10.0 e.u. (J mol^?1 K^?1), is observed between the two dissociation channels. This entropy difference corresponds to a negative 14.7±13.0 e.u. change for the dissociation of the dimer to give COT^?· and the neutral reference compound and a positive 10.9±8.4 e.u. entropy change for the dissociation of the dimer to give Ref^?· and neutral COT.     

An extended geminal model calculation of the dissociation energy of the ground state of Li2

The dissociation energy of the ground state of the Li₂ molecule has been calculated by using an extended geminal model. The calculated result is 1.024 eV and the experimental value is 1.048 ± 0.012 eV. the discrepancy can at least partly be attributed to a deficiency in the orbital basis set.     

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.     

X-ray photoelectron spectra of dinitrogen chelating ligands with some transition metals

The complexes of two chelating agents, CDTA (trans-1,2-cyclohexanediaminetetraacetic acid) and EDTA (ethylenediaminetetraacetic acid), with Ni(II), Co(II) and Cu(II) are studied by means of X-ray photoelectron spectroscopy (XPS). The N1s spectrum of CDTA has two components at 398.5 (±0.2 eV) and 400.9 (±0.2 eV) while only one signal is found after coordination at 400.0±0.2 eV. EDTA shows a N1s spectrum with one component at 400.9±0.2eV. A negative shift of about -1.3eV is observed in its complexes. The results are compared with the literature data on the complexes in the solid state.     

The electrical conductivity and magnetic susceptibility of germanium(II) monoselenide in the solid and liquid states

The specific conductivity of germanium(II) monoselenide has been measured, under equilibrium pressure, from room temperature to 802°C. Interpretation of the results leads to the conclusion that the intrinsic conductivity is observed in the solid in the upper temperature range: the calculated energy gap is E_0g = 1.222 ± 0.027 eV which coincides with the value of the optical gap. In liquid GeSe the calculated energy gap is 1.504 ± 0.016 eV. This increase of the energy gap in liquid GeSe is due, presumably, to the strengthening of the intralayer bonds of the structure. Electrical conductivity and magnetic susceptibility measurements confirm the existence of a polymorphic transformation in GeSe at 656°C.     

Photoelectron spectrum of hypofluorous acid,HOF

The photoelectron spectrum of HOF has been obtained with He I resonance radiation. Three bands were observed, which can be interpreted by analogy to the diatomic halogens, and to the recently reported CIF. The first two bands can be identified with the out-of-plane and in-plane components of the π_g-like outermost orbital of the diatomic halogens, split by the C_s symmetry of HOF. The first ionization potential is found to be 12.69 ± 0.03 eV, in close agreement with the photoionization value 12.71 ± 0.01 eV.     

Photoelectron spectroscopic study of simple hydrogen-bonded dimers. I. Supersonic nozzle beam photoelectron spectrometer and the formic-acid dimer

In this paper we describe several characteristics of our supersonic nozzle beam photoelectron spectrometer recently constructed for studying hydrogen-bonded dimers in the gas phase by HeI (58.4 nm) radiation. Using this photoelectron apparatus, we have reinvestigated the HeI photoelectron spectrum of the formic-acid dimer (HCOOH)₂ which is well known as a fairly strong doubly hydrogen-bonded dimer. It was found that the (HCOOH)₂ spectrum deduced here from the spectrum of the monomer—dimer mixture considerably differs from that reported by Carnovale et al. in the region beyond 16.5 eV. New spectral assignments are given for four ionization bands beyond 16.5 eV. It is also indicated that the lower bound of the dissociation energy of (HCOOH)₂⁺ is estimated to be 1.0 ± 0.1 eV from the threshold of the dimer band (11.0 eV) obtained in this experiment. This value is considerably smaller than the value of 1.7 ± 0.2 eV recently reported for the water dimer cation (H₂O)₂⁺.     

Lyman-α excitation spectra in the photodissociation of the doubly excited states of H2

A Lyman-α excitation spectrum has been observed using synchrotron radiation in the energy region corresponding to the double electron excitation of H₂. There exist in the spectrum three thresholds at 26.6±0.5 eV, 29.2±0.7 eV and 30.9±0.6 eV, and a dip at 34.1±0.5 eV. A Lyman-α excitation spectrum in the energy region corresponding to the single electron excitation has been also observed using a detection system which works as a band pass filter for detecting of Lyman-α fluorescence. The cross section of Lyman-α fluorescence in the photodissociation of the doubly excited states is very small, e.g., in the order of 10^?20 cm² at 30 eV, in comparison with that from the single electron excitation.     

Thermochemistry of molecular FeO,FeO+ and FeO

The gaseous oxides FeO and FeO₂ were identified by mass spectrometry as components of the effusion beam from a cell containing, initially, solid Fe₂O₃. From studies of gaseous equilibria involving these species, the dissociation energiesD₀⁰(FeO) = 96.8 ± 3 kcal (4.20 ± 0.13 eV) andD₀⁰(FeO₂) = 199.0 ± 5 kcal (8.64 ± 0.22 eV) were derived. The ionization potential of FeO was found to be 8.71 ± 0.10 eV, leading toD₀⁰(Fe⁺-O) = 78.2 ± 4.6 kcal (3.39 ± 0.20 eV).     

Photoionization of aqueous indole: Conduction band edge and energy gap in liquid water

Previous work on the determination of the photoionization threshold (I_sol) of tryptophan has now been extended to indole as a solute, both in tetramethylsilane (TMSi) and H₂O solvents. In TMSi, electron scavenging by N₂O or photoconductivity measurements lead to the same I_sol value: 4.95 ± 0.1 eV. In water, I_sol is found equal to 4.35 ± 0.1 eV. From these experiments, information on the ionization mechanism, on the oxidized solute and on the solvent can be gained: (i) the scavenger electron affinity does not intervene in the energy balance providing I_sol; (ii) an “effective” ionic radius of indole (1.40 Å) is estimated which suggests that the positive charge remains highly localized on the N-atom of the indole ring; (iii) a value of ?1.2 ± 0.1 eV can be deduced for V_o, the conduction band edge of water; (iiii) from the above findings, the energy gap E_G of pure water, considered as a semi-conductor, would be close to 7 eV. Such a result is discussed in terms of literature data pertaining to electron ejection in pure liquid water and X-ray photoelectron spectroscopy of amorphous ice.     

Dissociation cross sections of silane and disilane by electron impact

The total dissociation cross sections for silane and disilane are reported for electron energies above their ionization thresholds up to 110 eV. The measurements are derived from a kinetic analysis of silane and disilane dissociation in a constant-flow multipole dc plasma reactor. The methane dissociation cross section was also measured and found in agreement with published data. Maxima for silane and disilane, occurring around 60 eV, are respectively (1.2±3)×10^?15 cm² and (2.6±0.6)× 10^?15 cm². Total ionization cross sections are also measured and above 50 eV the ratios of dissociative ionization to dissociation cross sections are 0.5±0.1 and 0.25±0.10 respectively for silane and disilane. The probability for silane elimination in the disilane fragmentation reaches a maximum of 0.8 at 19 eV and decreases down to 0.5 at 100 eV. Dissociation processes of silane and disilane are discussed in comparison with methane and ethane     

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.     

On the heat of formation of [C6H4]+˙

The appearance energy of the [C₆H₄]^+˙ ion from benzonitrile has been measured, using an electron monochromator. The value observed at onset, 12.54±0.03 eV, leads to a heat of formation of 1304±3 kJ mol^?1. Possible reasons for widely divergent values reported previously are proposed.