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.     

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.     

ChemInform Abstract: Photoelectron Spectroscopy of BH- 3.

The photoelectron spectra of BH₃^- and BD₃^- are studied and the electron affinities of borane are determined to be EA(BH3) = 0.038 eV and EA(BD3) = 0.027 eV.     

Intramolecular Photo-Oxidation as a Potential Source to Probe Biological Electron Damage: A Carboxylated Adenosine Analogue as Case Study

A carboxylated adenosine analog (C-Ado⁻) has been synthesized and probed via time-resolved photoelectron spectroscopy in order to induce intra-molecular charge transfer from the carboxylic acid moiety to the nucleobase. Intra-molecular charge transfer can be exploited as starting point to probe low-energy electron (LEE) damage in DNA and its derivatives. Time-dependent density functional theory (TD-DFT) calculations at the B3LYP-6311G level of theory have been performed to verify that the highest occupied molecular orbital (HOMO) was located on carboxylic acid and that the lowest occupied molecular orbital (LUMO) was on the nucleobase. Hence, the carboxylic acid could work as electron source, whilst the nucleobase could serve the purpose of electron acceptor. The dynamics following excitation at 4.66 eV (266 nm) were probed using time-resolved photoelectron spectroscopy using probes at 1.55 eV (800 nm) and 3.10 eV (400 nm). The data show rapid decay of the excited state population and, based on the similarity of the overall dynamics to deoxy-adenosine monophosphate (dAMP^–), it appears that the dominant decay mechanism is internal conversion following ¹ππ* excitation of the nucleobase, rather than charge-transfer from the carboxylic acid to the nucleobase.     

UV photoelectron and ab initio quantum mechanical characterization of nucleotides: The valence electronic structure of anionic 2′-deoxyadenosine-5′-phosphate

He(I) ultraviolet (UV) photoelectron spectroscopy and ab initio, self-consistent field (SCF) calculations with the 6-31G basis set have been employed to characterize the valence electronic structures of anionic 2′-deoxyadenosine-5′-phosphate (5′-dAMP⁻). Theoretical ionization potentials (IPs) of 5'-dAMP^-, of the neutral model compounds 9-methyladenine (9-MeA) and 3-hydroxytetrahydrofuran (3-OH-THF), and of the model anion CH₃HPO₄⁻ have been obtained by applying Koopmans' theorem to ab initio SCF results. The ionization potentials predicted from the SCF calculations have been compared to He(I) photoelectron spectra of 9-MeA and 3-OH-THF. The SCF calculations predict a value (8.45 eV), for the highest occupied π orbital in 9-MeA which agrees well with the experimental vertical IP (8.39 eV). However, IPs for the highest occupied lone-pair orbitals in 3-OH-THF are predicted to be more than 1.52 eV higher than the experimental IPs. Results from recently reported [H. S. Kim and P. R. LeBreton, Proc. Natl. Sci. USA 91, 3725–3729 (1994), and N. S. Kim and P. R. LeBreton, J. Am. Chem. Soc., 118, 3694 (1996)] second-order Møller-Plesset perturbation (MP2) calculations and configuration interaction calculations using the configuration interaction singles (CIS) method indicate that configuration interaction effects strongly influence the energies of the first five ionization events arising from removal of electrons from the closed-shell model anion CH₃HPO₄⁻. Results from the 6-31G SCF calculations of 5′-dAMP⁻, 9-MeA, 3-OH-THF, and CH₃HPO₄⁻ indicates that valence orbital electron distributions in the nucleotide and in the model compounds and anion are similar. The correspondence between the orbital structure of the nucleotide, and the model compounds and anion makes it possible, employing experimental photoelectron data and MP2/CIS computational results for the model compounds and anion, to individually correct IPs calculated for the nucleotide at the 6-31G SCF level. Here, this approach has provided values for the 13 lowest IPs of 5′-dAMP⁻ and indicates that the first IPs of the base, sugar, and phosphate groups are 6.1, 7.8, and 5.5 eV, respectively. © 1996 John Wiley & Sons, Inc.     

Photoelectron spectra of quaternary salts in solution

The ionisation energies, measured by He(I) photoelectron spectroscopy, are reported for I^?, Cl^?, Br^?, CNS^? and NO^?₂ in adiponitrile solution. These energies give a straight line when plotted against the energies of the electron transfer to solvent absorption bands of the ions in acetonitrile solution. The intercept gives the electron affinity of the solvent; for acetonitrile, assumed to be spectroscopically equivalent to adiponitrile, the electron affinity is found to be 1.85 eV; for water it is 1.65 eV. The energies of electron transfers not observable in the UV absorption spectrum of NO^?₂ solutions are estimated from the photoelectron spectra.     

Laser photoelectron spectrometry of CH−

Fixed-frequency laser photoelectron spectrometry has been utilized to study photodetachment of CH^? ions by 4880 A laser radiation. Transitions involving low-lying excited states of ¹Δ and ⁴Σ^? symmetry have been observed for CH^? and CH, respectively. The electron affinity of CH was determined to be (1.238 ± 0.008) eV. The a ⁴Σ^? CH term energy was found to be (0.742 ± 0.008) eV and other spectroscopic constants for X³Σ^?CH^?, a ¹ΔCH^?, and a ⁴Σ^?CH have been determined.     

Photoelectron spectrum and ground state electronic structure of chromyl chloride vapor

The electronic structure of chromyl chloride CrO₂Cl₂ has been investigated by ultraviolet (HeI) photoelectron spectroscopy. Mulliken-Wolfsberg-Helmholtz molecular orbital calculations have been performed in order to provide a model for interpretation of the photoelectron spectra and to assist in assigning the low-energy optical absorption and emission transitions. The first ionization potential of CrO₂Cl₂ at 11.8 eV is due to ionization of the near-degenerate oxygen and chlorine nonbonding 2a₂, 4b₁, and 4b₂ MO's. The first unoccupied orbital is basically a chromium dπ^* orbital. The excitations (2a₂, 4b₁, 4b₂)→ 7a₁^* correlate well with the three low energy absorption transitions observed.     

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.     

Effect of Ar+, He+, and S+ Irradiation on n-InP Single Crystal

The irradiation effects of Ar⁺, He⁺, and S⁺ with energy from 10 eV to 180 eV on n-InP(100) surface are analyzed by X-ray photoelectron spectroscopy and low energy electron diffraction. After irradiation on the n-InP surface, damage on the surface, displacement of the Fermilevel and formation of sulfur species on S⁺ exposed surface are found and studied. Successive annealing is done to suppress the surface states introduced by S⁺ exposure. However, it is unsuccessful in removing the damage caused by noble ions. Besides, S⁺ ions can efficiently repair the Ar⁺ damaged surface, and finally form a fine 2×2 InP surface.     

Supramolecular Formation of Li+@PCBM Fullerene with Sulfonated Porphyrins and Long‐Lived Charge Separation

Lithium‐ion‐encapsulated [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester fullerene (Li⁺@PCBM) was utilized to construct supramolecules with sulfonated meso‐tetraphenylporphyrins (MTPPS^4?; M=Zn, H₂) in polar benzonitrile. The association constants were determined to be 1.8×10⁵ M ^?1 for ZnTPPS^4?/Li⁺@PCBM and 6.2×10⁴ M ^?1 for H₂TPPS^4?/Li⁺@PCBM. From the electrochemical analyses, the energies of the charge‐separated (CS) states were estimated to be 0.69 eV for ZnTPPS^4?/Li⁺@PCBM and 1.00 eV for H₂TPPS^4?/Li⁺@PCBM. Upon photoexcitation of the porphyrin moieties of MTPPS^4?/Li⁺@PCBM, photoinduced electron transfer occurred to produce the CS states. The lifetimes of the CS states were 560 μs for ZnTPPS^4?/Li⁺@PCBM and 450 μs for H₂TPPS^4?/Li⁺@PCBM. The spin states of the CS states were determined to be triplet by electron paramagnetic resonance spectroscopy measurements at 4 K. The reorganization energies (λ) and electronic coupling term (V) for back electron transfer (BET) were determined from the temperature dependence of k_BET to be λ=0.36 eV and V=8.5×10^?3 cm^?1 for ZnTPPS^4?/Li⁺@PCBM and λ=0.62 eV and V=7.9×10^?3 cm^?1 for H₂TPPS^4?/Li⁺@PCBM based on the Marcus theory of nonadiabatic electron transfer. Such small V values are the result of a small orbital interaction between the MTPPS^4? and Li⁺@PCBM moieties. These small V values and spin‐forbidden charge recombination afford a long‐lived CS state.     

Photoelectron spectra studies of organic free radicals. The nitroxide radical

The photoelectron spectra of the nitroxide radicals, di-tert-butylnitroxide (DTBN) and 2,2,6,6-tetramethyl-piperidine-N-oxyl, have been studied and molecular orbital calculations made. The adiabatic first ionization potentials were found to be 6.77 and 6.73 eV for these two nitroxide radicals respectively. Four vertical ionization potentials which are common to each nitroxide radical were attributed to ionization of the odd electron in the NO anti-bonding π orbital, oxygen lone pair electrons and NO bonding π electrons. Doublet splitting of the lone pair electron peak with different peak intensities can be quantitatively understood in terms of triplet and singlet states of the photoionized nitroxide cation.     

Closed and open-shell atomic oxygen on silver: two distinct patterns of the O<Subscript>1s</Subscript> binding energy and X-ray absorption O <Emphasis Type="Italic">K</Emphasis>-edge spectra as revealed by density functional theory

The electronic structure of atomic oxygen adsorbed species is studied by means of the density functional theory in the context of the ethylene epoxidation on the silver surface. The adsorbed oxygen species are modeled by the Ag₂O molecule either in its closed (¹A₁) or open-shell states (³B₁ and ¹B₁). In both open-shell states the 1s level appears to be lower than that in ¹A₁ by about 2 eV. This is apparently a sequence of the separation of electron pair, occupying the *-type highest occupied molecular orbital (HOMO), decreasing the electron density at the oxygen center. Such variation of the O_1s level for closed and open-shell Ag₂O states seems to explain the X-ray photoelectron spectroscopy (XPS) data concerning two distinct atomic oxygen species on silver surface having the O_1s binding energy of about 528 and 530 eV, called nucleophilic and electrophilic oxygen, respectively. The X-ray absorption O K-edge spectra (XANES) calculated for two types of the Ag₂O states by means of multiple-scattered-X-based approach appears to be in a qualitative agreement with those experimentally recorded for nucleophilic and electrophilic oxygen.     

Photoelectron-spectroscopic Evidence Concerning “Homo-aromaticity”

The first of the two π-bands in the photoelectron spectrum of cis-cis-cis-1, 4, 7-cyclononatriene (I, symmetry C_3v) shows a Jahn-Teller split. This is consistent with the prediction of molecular orbital theory that the top occupied orbitals of I are e (π) and a ₁(π) respectively. From the difference ?( e (π)) - ?( a ₁(π)) = 0.90 to 0.97 eV a value of β_1,3 = ?0.68 eV = 0.27 β (β = -2.5 eV) is obtained for the homoconjugative interaction of two π-orbitals in I. This value represents almost exclusively through-space interaction between the π-orbitals. Through-bond interaction (hyperconjugation) is a minor effect in I. A comparison of the photoelectron data of bicyclo [4.2.1] nonatriene with those of norbornene and cycloheptadiene shows that homoconjugation (homo-aromaticity) can only be detected by photoelectron spectroscopy if the interacting π-bonds (basis orbitals) are symmetry equivalent or have accidentally (almost) degenerate energies.     

(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.     

Angle- and spin-resolved photoelectron spectroscopy of thepπ outer valence shell of HBr molecules

Using circularly polarized synchrotron radiation, the photoionization of HBr molecules was studied by angle- and spin-resolved photoelectron spectroscopy in the photon energy range from 11.7 eV to 21 eV. For photoelectrons corresponding to the final ionic states HBr⁺ X ²Π_3/2(v=0) andX ²Π_1/2(v=0), the energy dependence of the dynamical photoionization parameters was measured and compared with ab initio calculations for HBr⁺ by Raseev et al. and RRPA calculations for Kr⁺ by Huang et al., This comparison indicates that, for energies above the electronic autoionization region, photoemission from the outer valence orbital exhibits distinct atomic behavior. By combining the experimental data for the cross section σ and the spin polarization parameter A, sums of partial cross section contributions to σ were determined and analyzed to obtain specific information on the outgoing partial electron waves. Furthermore, the validity of the so-called non-relativistic relationships for the dynamical photoionization parameters was tested as a function of equal photon and kinetic photoelectron energy, respectively.     

‘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 ⁺.     

Photoemission from matrix-isolated nickel atoms

UV photoelectron spectra from Ni atoms isolated in a xenon matrix at 9 K have been measured for the first time using Hell (40 8 eV). Two peaks have been found at 2.8 and 4.6 eV below E_F, which are interpreted as being due to different d⁸s¹ final states of the Ni ion. including a relaxation shift of 2.0 eV. The existence of atomic Ni species in the matrix has been verified by in situ optical absorption spectra.     

Photoelectron Imaging Spectroscopy of ZrO- Diatomic Anion

The diatomic ZrO^- anion has been prepared by laser ablation and studied by photoelectron imaging spectroscopy combined with quantum chemistry calculations. The observed photoelectron spectra can be well assigned on the basis of reported optical spectroscopy and high-level ab initio calculations. The ground state of ZrO^- is a ²△ state with spin-orbit splitting of 578±12 cm^-. The electron affinity of ZrO is 1.249±0.005 eV. For the first time, the c³Σ^- state of ZrO has been experimentally observed at 13316±24 cm^- with respect to the X¹∑⁺ ground state. A comparison between ZrO and the isoelectronic molecule NbN has been made.     

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.