High-resolution Photoelectron Spectra Research Articles

High-resolution soft X-ray photoelectron spectroscopy of liquid water

High-resolution soft X-ray photoelectron spectra of liquid water (H(2)O and D(2)O) were measured using a liquid beam photoelectron spectrometer. The 1a(1) (O1s) band and the lowest valence 1b(1) band had single peaks, which is not consistent with the split 1b(1)→ 1a(1) of the X-ray emission band of liquid water if the splitting is assumed to originate from level shifts in two different hydrogen bonding structures. The second valence 3a(1) band of liquid water exhibited a flat top implying that two bands exist underneath a broad feature, which is similar to the case of the 3a(1) band of amorphous ice. The energy splitting between the two 3a(1) bands is estimated to be 1.38 eV (H(2)O) and 1.39 eV (D(2)O). Ab initio calculations suggest that the large splitting of the 3a(1) band is characteristic of water molecules that function as both proton donor and acceptor. The overall result is consistent with the conventional model of a tetrahedral hydrogen-bonding network in liquid water.

Evaluation of Asphaltene Degradation on Highly Ordered TiO2 Nanotubular Arrays via Variations in Wettability

Photocatalytic degradation of both aquatic and atmospheric organic pollutants on titanium dioxide has been extensively investigated in the past decades, but research on direct photocatalytic degradation of solid-phase organic pollutants is rather limited. In this work, photocatalytic degradation of n-C(7) asphaltene, which is composed of solid-phase organic substances found in crude oil, on highly ordered TiO(2) nanotubular arrays (TNAs) was studied using the wettability as an indicator. It was observed that the water contact angle rose linearly with increasing the concentration of n-C(7) asphaltene solution up to 0.02 g mL(-1). Further increasing the concentration of n-C(7) asphaltene only caused small augment in the contact angle, which eventually became stable around 98°. It is demonstrated that the water contact angle can be used as an indicator to reflect the residual solid-phase organic pollutants within a certain range of pollutant concentration. As observed, n-C(7) asphaltene film degraded on TNAs under UV illumination for 60 min, showing complete mineralization of ∼80% of n-C(7) asphaltene that was released into air finally. The remaining 20% of asphaltene was partially decomposed into smaller organic molecules, e.g., -C(═O)- and -C(═O)-OH, confirmed by high-resolution X-ray photoelectron spectra analysis. TNAs can be reused to degrade the solid-phase n-C(7) asphaltene for a number of cycles without further treatment.

Coherent phase control of (2+1) resonantly enhanced multiphoton ionization photoelectron spectroscopy

In this work, we report a theoretical study of the coherent phase control of typical (2+1) resonantly enhanced multiphoton ionization photoelectron spectroscopy (REMPI-PES) in an atomic system. By properly designing the spectral phase of a femtosecond pulse, we can realize the manipulation of the photoelectron energy, the photoelectron spectral bandwidth and the photoelectron intensity at a certain kinetic energy. Moreover, we can also obtain a high-resolution photoelectron spectrum and fine energy-level structure of the excited states for a complicated quantum system in spite of the broad-width spectrum of the femtosecond pulse. The theoretical results have promising applications for investigating the molecular structure and understanding the laser-induced ionization dynamics.

Slow Photoelectron Velocity-Map Imaging of the i-Methylvinoxide Anion

High-resolution photoelectron spectra of the i-methylvinoxide anion are obtained by slow electron velocity-map imaging. The transitions between the anion ground electronic state, X̃ (1)A', and the radical X̃ (2)A'', and à (2)A' states are measured. Franck-Condon simulations of the X̃ (2)A'' ← X̃ (1)A' transition are performed to aid in assigning peaks, yielding several vibrational frequencies for the first time. Additional structure in the spectrum of the X̃ (2)A'' ← X̃ (1)A' transition is attributed to hindered rotor motion of the methyl group. Simulation of methyl torsional states allows identification of the true origin peak, yielding the experimental adiabatic electron affinity, EA = 1.747 ± 0.002 eV, and the à state term energy, T(0) = 1.037 ± 0.002 eV. Comparison with the fully deuterated isotopologue further supports the assignment of hindered rotor progressions. The favored methyl rotor position is eclipsed in the radical X̃ state and staggered in the anion X̃ and radical à states.

Slow photoelectron velocity-map imaging of the CnH− (n = 5–9) anions

High-resolution photoelectron spectra of the CnH− anions with n = 5–9 are acquired with slow electron velocity-map imaging (SEVI). Spectral features are assigned with the help of electronic structure calculations and Franck–Condon simulations. Well-resolved transitions to the linear 2Π and ã4Σ− neutral states are observed for species with an odd number of carbon atoms. For C6H− and C8H−, transitions to the 2Π neutral ground state and the low lying Ã2Σ+ excited state are observed. Precise electron affinities, term energies, fine structure splittings, and gas-phase vibrational frequencies are determined. The C5H−, C7H− and C9H− SEVI spectra are consistent with the anions having 3Σ− linear triplet ground states.

Vibronic Structure of the Formyloxyl Radical (HCO2) via Slow Photoelectron Velocity-Map Imaging Spectroscopy and Model Hamiltonian Calculations

We report high-resolution photoelectron spectra of HCO(2)(-) and DCO(2)(-) obtained with slow photoelectron velocity-map imaging. Well-resolved photodetachment transitions to the (2)A(1) and (2)B(2) states of the neutral radicals were observed. In addition, vibronic levels of the HCO(2) and DCO(2) radicals with up to 2000 cm(-1) of internal energy were calculated using a quasidiabatic Hamiltonian approach and high-level ab initio calculations. Spectral simulations using the calculated levels were found to be in excellent agreement with the experimental spectra and used to assign many of its features. This study unambiguously determined that the (2)A(1) state is the ground state of both HCO(2) and DCO(2), in contrast to earlier work that indicated the (2)B(2) state was the ground state for DCO(2). For both isotopologs, the (2)B(2) state is a very low-lying excited state with term energies of T(0) = 318 +/- 8 cm(-1) for HCO(2) and T(0) = 87 +/- 8 cm(-1) for DCO(2). The adiabatic electron affinities are determined to be EA(HCO(2)) = 3.4961 +/- 0.0010 eV and EA(DCO(2)) = 3.5164 +/- 0.0010 eV.

Interaction Potentials, Spectroscopy, and Transport Properties of the Br+−RG Systems (RG = He−Ar)

The potential energy curves of Br cations interacting with rare gas (RG = He-Ar) atoms are calculated employing the RCCSD(T) technique for the non-spin-orbit states, with spin-orbit coupling being included analytically, using an atoms-in-molecule approach. The curves are calculated employing large basis sets extrapolated to the complete basis set limit, and the energies are corrected for basis set superposition error. Comparison is made to the limited potentials available previously. Gaseous ion mobilities are obtained using the potential energy curves of the states of the complex that correlate to the Br(+)((3)P(J)(o)) + RG asymptotes. Excellent agreement is obtained with the experimental data in He; however, the experimental error bars are such that we are unable to determine which spin-orbit state(s) are present in the mobility measurements. Finally, a high-resolution photoelectron spectrum is simulated for the ionization of Br-Ar.

Study of KrO− and KrO via Slow Photoelectron Velocity-Map Imaging Spectroscopy and ab Initio Calculations

The high-resolution photoelectron spectrum of KrO(-) was obtained using slow electron velocity-map imaging (SEVI). The SEVI spectrum reveals numerous vibronic transitions between multiple electronic states of KrO(-) and KrO, both of which are open-shell species. Detailed assignments are made by comparison with theoretical simulations based on high level ab initio calculations and an atoms-in-molecule model that accounts for spin-orbit coupling in the anion and neutral. Several KrO(-) and KrO vibrational frequencies and excited-state term energies are accurately determined from the analysis of the experimental spectra and are found to be in good agreement with the calculated values.

Slow photoelectron velocity-map imaging spectroscopy of the vinoxide anion

High resolution photoelectron spectra of the vinoxide anion are obtained by slow electron velocity-map imaging. Transitions between the anion X (1)A(') ground electronic state and the radical X (2)A(") and A (2)A(') states are observed. This experiment yields a precise value of 1.8250+/-0.0012 eV for the adiabatic electron affinity and 0.996+/-0.003 eV for the A-X term energy of the vinoxy radical. Franck-Condon simulations of the X (2)A(") <-- X (1)A(') transition are performed at varying levels of approximation. Full treatment with Duschinsky rotation is necessary to reproduce experimental results. Comparison of the experimental and simulated spectra leads to the assignment of previously unresolved transitions, notably between levels of a(") symmetry.

Study of ArO− and ArO via Slow Photoelectron Velocity-Map Imaging Spectroscopy and Ab Initio Calculations

The high-resolution photoelectron spectrum of ArO(-) was obtained using slow electron velocity-map imaging (SEVI). The SEVI spectrum reveals well-resolved vibrational transitions between multiple electronic states of ArO(-) and ArO, both of which are open-shell species. These transitions occur within the broad envelope of previous lower resolution photoelectron spectra. Detailed assignments are made by comparison with theoretical simulations based on high level ab initio calculations and an atoms-in-molecule model that accounts for spin-orbit coupling in the anion and neutral. The adiabatic electron affinity of ArO is found to be 12481 +/- 2 cm(-1). Several ArO(-) and ArO vibrational frequencies and excited-state term energies are accurately determined from the analysis of the experimental spectra and are found to be in excellent agreement with the calculated values.

Slow photoelectron velocity-map imaging spectroscopy of C2N−, C4N−, and C6N−

High resolution photoelectron spectra of C(2)N(-), C(4)N(-), and C(6)N(-) anions are reported, obtained using slow electron velocity-map imaging. The spectra show well resolved transitions to the X (2)Pi neutral ground state of all three species and to the a (4)Sigma(-) excited state of C(2)N and C(4)N. This study yields the adiabatic electron affinity of C(2)N, C(4)N, and C(6)N, the spin-orbit splitting in the X (2)Pi state of each radical, and the term energy of the a (4)Sigma(-) state in C(2)N and C(4)N. Relatively little vibrational activity is observed, indicating small geometry changes upon photodetachment. This result, plus the observation of transitions to neutral quartet states, indicates that the C(2n)N(-) (n=1-3) anions all have linear (3)Sigma(-) ground states.

The O 1s photoelectron spectrum of molecular oxygen revisited

High-resolution photoelectron spectra of the inner-shell levels of molecular oxygen have been measured using synchrotron radiation. The vibrational structure of the two magnetically-split core-shell components is analyzed based upon ab initio calculations. The ratio between the intensities of the two components was analyzed at several different ionization energies up to about 600 eV, and the same is discussed and compared to high-energy ionization intensities. A theoretical calculation shows very good agreement with the measured spectra. The calculation implements a model where two parity components make up the 4Σ peak profile. The gerade–ungerade energy split for this state is found to be 50 meV.

Multiplet splitting patterns exhibited by the first row transition metal oxides in X-ray photoelectron spectroscopy

High resolution photoelectron spectra from transition metal ions in TiO 2, V 2O 5, VO 2, V 2O 3, MnO, Mn 2O 3, MnO 2, Cr 2O 3, FeO, CoO, NiO, CuO, Cu 2O, FeSrO 3, and Cu doped CaTiO 3 were re-examined using a constrained curve fitting approach. Effective fits of the multiplet splitting present could be attained for the oxides with unfilled 3d bands if multiple final states were assumed. The type of transitions implied, also suggest the classification of these oxides during core level photoelectron emission as either; Mott–Hubbard (V 2O 5, VO 2, V 2O 3, Cr 2O 3, and FeO), intermediate (MnO, Mn 2O 3, and MnO 2) or charge transfer type compounds (FeSrO 3, CoO, NiO, CuO and Cu doped CaTiO 3). These transitions along with relationships defining the splitting energy with respect to the total spin and binding energy are discussed.

Synthesis and Photocatalytic Activity of One-dimensional ZnO-Zn2SnO4 Mixed Oxide Nanowires

Mixed oxide photocatalysts, ZnO-Zn2SnO4 (ZnO-ZTO) nanowires with different sizes were prepared by a simple thermal evaporation method. The ZnO-ZTO nanowires were characterized with a scanning electron microscope, X-ray diffraction, high-resolution transmission electron microscopy, energy-dispersive spectrometer, and X-ray photoelectron spectra. The photocatalytic activity of the ZnO-ZTO mixed nanowires were studied by observing the photodegradation behaviors of methyl orange aqueous solution. The results suggest that the ZnO-ZTO mixed oxide nanowires have a higher photocatalytic activity than pure ZnO and Zn2SnO4 nanowires. The photocatalyst concentration in the solution distinctly affects the degradation rate, and our results show that higher photodegradation efficiency can be achieved with a smaller amount of ZnO-ZTO nanowire catalyst, as compared to the pure ZnO and ZTO nanowires. Moreover, the photocatalytic activity can also be enhanced by reducing the average diameter of the nanowires. The activity of pure ZnO and ZTO nanowires are also enhanced by physically mixing them. These results can be explained by the synergism between the two semiconductors.

Slow electron velocity-map imaging spectroscopy of the 1-propynyl radical

High resolution photoelectron spectra of the 1-propynyl and 1-propynyl-d(3) anions acquired with slow electron velocity-map imaging are presented. The electron affinity is determined to be 2.7355+/-0.0010 eV for the 1-propynyl radical and 2.7300+/-0.0010 eV for 1-propynyl-d(3). Several vibronic transitions are observed and assigned using the isotopic shifts and results from ab initio calculations. Good agreement between experimental spectra and calculations suggests a C(3v) geometry for the 1-propynyl radical. No evidence is found for strong vibronic coupling between the ground electronic state and the low-lying first excited state.

The Substituent Effect of the Methyl Group. Carbon 1s Ionization Energies, Proton Affinities, and Reactivities of the Methylbenzenes

High-resolution carbon 1s photoelectron spectra have been measured for methyl-substituted benzenes. By using these data together with molecular structure calculations to predict the vibrational profiles expected in the spectra, it has been possible for the first time to assign 1s ionization energies to each of the inequivalent carbon atoms in these molecules. There exist linear correlations between the ionization energies and the energy changes for other chemical processes, such as enthalpies of protonation and activation energies for hydrogen exchange and protodesilylation. There are deviations from these correlations for sites in which hyperconjugation plays a role in the process. These can be understood by recognizing that the core-ionization energies reflect primarily the Hammett parameter sigma whereas the other energies reflect sigma+. The ionization and reaction energies can be summarized compactly with a linear model in which the total effect of the substituents is equal to the sum of the effects of the individual substituents. A slightly better description is obtained with a quadratic model, which allows for interaction between the substituents.

Satellite structures of Kr and Xe studied by high-resolution threshold photoelectron spectroscopy

A high-resolution threshold photoelectron spectrum of Xe was measured in the photon energy region of the 5s25p4nl states. The peak width of the measured Xe 5s−1 main line was close to 5 meV. A previously measured spectrum of Kr was also analysed. Rich satellite peaks were clearly observed, including many peaks not observed in previous optical, photoelectron and threshold photoelectron studies. The satellite peak energies and their assignments for Kr and Xe are listed. The observed Rydberg series converging to the Xe2+ ground state was assigned to the (3P2)ng series by detailed analysis. The energy level of the Xe2+ 3P2 state as the converging limit of the observed Rydberg series was obtained as 38.355 eV.

In situ high-resolution valence photoelectron spectra of a peanut-shaped C60 polymer

To elucidate the origins of the metallic properties of the peanut-shaped C60 polymer, we examined the valence photoelectron spectra of the polymer using in situ high-resolution photoelectron spectroscopy and found that the density-of-states (DOS) of the polymer clearly comes across the Fermi edge in a manner similar to that of Au film used as a reference, indicating that the peanut-shaped C60 polymer exhibits metallic properties.

String excitations of a hole in a quantum antiferromagnet and photoelectron spectroscopy

The aim of the present paper is twofold. The first goal is to show that high resolution angle-resolved photoelectron spectra from cuprates indicate the presence of string-like excitations of the quasihole excitation in a quantum antiferromagnet. In order to compare with the experimental intensity plots, we calculate the spectral function of the t-J and the t-t'-t"-J models within the self-consistent Born approximation for widely accepted values of the parameters of these models. The main features of the high resolution photoelectron spectra are in general agreement with the results based on the above models and can be understood by considering not only the lowest energy quasiparticle peak but, also, the higher energy string-like excitations of the hole. The second goal of the present paper is to make the case that a proper analysis of both the numerical results obtained from these models and of the experimental results, suggests a theoretical picture for the internal structure of the hole-quasiparticle and a string-exchange pairing mechanism due to strong antiferromagnetic correlations among the background spins. We find that, using a simple model in which the Hilbert space is restricted to states of only unbroken strings attached to the holes and in which the holes are connected with unbroken strings, we can provide a good quantitative description of the most accurate numerical results. We find that the holes experience an effective interaction due to a string-exchange mechanism which is characterized by a rather large string tension and this can provide pairing energy scales much larger that those suggested by spin-fluctuation mediated pairing models. In addition, it is argued that such string-exchange interaction tends to bind holes in a bound state with the $d_{x^2-y^2}$ symmetry.

A study of the formation and oxidation of PtSi by SR–PES

In the paper we present the results on the formation of platinum silicide (PtSi) by means of synchrotron radiation photoelectron spectroscopy (SR–PES) and show the effect of a Pt/Si sample exposure to both a low and high-pressure oxygen atmosphere at the end of an annealing process. We have carried out a detailed analysis of high resolution photoelectron spectra of the Pt 4f and Si 2p peaks which were taken during the sample annealing at specific temperatures. In addition to the generally known Pt 2Si and PtSi phases we have recognized an additional intermediate phase during the formation of Pt 2Si and attributed it to the Pt 3Si phase. We have proved that silicon diffuses towards the sample surface. The results of a low-pressure oxygen experiment have shown that oxygen binds only to surface silicon, however, in the case of a PtSi sample prepared externally in the ON Semiconductor labs under nitrogen/oxygen atmosphere oxygen binds not only to surface silicon but also takes over Si atoms out of the PtSi phase which results in the formation of a SiO 2 layer on almost pure platinum.