Penning Ionization Electron Spectroscopy Research Articles

Penning ionization electron spectroscopy of anisole, thioanisole, and selenoanisole by collision with He*(23S): Conjugation effects and conformational stability

The electronic structures of chalcogenoanisole C6H5XCH3 (X = O, S, and Se) have been determined by Penning ionization electron spectroscopy experiments with density functional theory (DFT), multi-configuration molecular orbital, and natural bond orbital (NBO) calculations. Ionization energies and electron distributions outside molecular surfaces were calculated by outer valence Green's functions (OVGF) and exterior electron density (EED) calculations, respectively. The PIES spectra and calculations allow characterizations of conformational potential with respect to the Cring-X bond. It has been found that selenoanisole is in the vertical from. The σ-π interaction is calculated to become stronger on going X = O → S → Se.

Penning spectroscopy and structure of acetylene oligomers in He nanodroplets.

Embedded atoms or molecules in a photoexcited He nanodroplet are well-known to be ionized through inter-atomic relaxation in a Penning process. In this work, we investigate the Penning ionization of acetylene oligomers occurring from the photoexcitation bands of He nanodroplets. In close analogy to conventional Penning electron spectroscopy by thermal atomic collisions, the n = 2 photoexcitation band plays the role of the metastable atomic 1s2s 3,1S He*. This facilitates electron spectroscopy of acetylene aggregates in the sub-Kelvin He environment, providing the following insight into their structure: the molecules in the dopant cluster are loosely bound van der Waals complexes rather than forming covalent compounds. In addition, this work reveals a Penning process stemming from the n = 4 band where charge-transfer from autoionized He in the droplets is known to be the dominant relaxation channel. This allows for excited states of the remnant dopant oligomer Penning-ions to be studied. Hence, we demonstrate Penning ionization electron spectroscopy of doped droplets as an effective technique for investigating dopant oligomers which are easily formed by attachment to the host cluster.

Electron momentum spectroscopy study on the valence electronic structure of methyl formate.

We report an electron momentum spectroscopy study on methyl formate. A symmetric noncoplanar (e, 2e) experiment has been performed at an incident electron energy of 1.2 keV and electron momentum profiles of the valence orbitals have been obtained. On the basis of the result, assignments of the 10a'-1 and 1a″-1 bands have been made to resolve a contradiction between photoelectron spectroscopy and Penning ionization electron spectroscopy studies. Comparisons between experiment and theory reveal that the influence of the molecular vibration has to be taken into account for a proper understanding of the electron momentum profiles. Contributions of individual vibrational normal modes have also been investigated in detail by means of the harmonic analytical quantum mechanical approach.

Syntheses, Geometrical and Electronic Structure of Alkyladamantanes and Their Thermodynamic Characteristic According to the Density Functional Theory

Propyladamantanes synthesized by of alkylation adamantane with isopropyl alcohol temperature range from 5 to 40°C in the presence of 96% sulfuric acid. Tetramethyl- and Dimethylethyladamantanes synthesized by of isomerization of Perhydroanthracene in the presence of aluminium oxide catalyst on the setting of the flow type. Isomers Butyladamantanes was obtained by the reaction of alkylation of the adamantane with n-butane and isobutane. Adamantane and its derivatives have been the subject of many experimental and theoretical studies. The molecular structure of adamantane was studied by gasphase electron diffraction, Penning ionization electron spectroscopy, photoelectron spectroscopy, electron spin resonance, and quantum calculations of ionization potentials (IP) and electron affinity (SE). The structure 1-n-propyladamantane (1), 1-isopropyladamantane (2), 2-n-propyladamantane (3), 1,2-di-n-propyladamantane (4), 1,3-dimethyl-5-ethyladamantane (5), 1,3,5,6-tetramethyladamantane (6), 1,3,5,7-tetramethyladamantane (7), perhydroanthracene (8), 1-n-butyladamantane (9), 1-isobutyladamantane (10), 1-sec-butyladamantane (11) has been studied using the Becke–Lee–Yang–Parr (B3LYP) hybrid energy functional of electron density with the 6-31G* basis set. The geometric and electronic characteristics of the compounds and their total energy, normal vibration frequencies have been calculated. It has been shown that the calculated Gibb free energies of formation for the perhydroanthracene isomerization products are in qualitative agreement with the experimental product composition of the isomerate and alkylation of adamantane with isopropyl alcohol are in qualitative agreement with the experimental composition of the products. Obtained good agreement of calculated and experimental data on the composition of equilibrium mixtures.

Intermolecular potential energy surfaces for the interaction between H2X (X[dbnd]O, S) and a metastable Ne*(3P2,0) atom

Potential energy surfaces for the interaction of a Ne*(3P2,0) atom with H2O and H2S molecules are obtained on the basis of a semi empirical method that has been previously used for some specific orientations in Ne*(3P2,0)–H2O system. The method is now suitable for all orientations and also for Ne*(3P2,0)–H2S system. Interesting features emerge by comparing the two systems and appear related to different characteristics of the two molecular partners. The potential energy surface for Ne*(3P2,0)–H2S has been also successfully tested for reproducing recent experimental Penning ionization electron spectroscopy data, sensible to some specific orientations of the two colliding partners.

Penning ionization electron spectroscopy of hydrogen sulfide by metastable helium and neon atoms.

The dynamics of the Penning ionization of hydrogen sulfide molecules by collision with helium and metastable neon atoms, occurring in the thermal energy range, has been studied by analyzing the energy spectra of the emitted electrons obtained in our laboratory in a crossed beam experiment. These spectra are compared with the photoelectron spectra measured by using He(I) and Ne(I) photons under the same experimental conditions. In this way we obtained the negative energy shifts for the formation of H2S(+) ions in the first three accessible electronic states by He*(2(3,1)S1,0) and Ne*((3)P2,0) Penning ionization collisions: the 2b1 (X̃(2)B1) fundamental one, the first 5a1 (Ã(2)A1), and the second 2b2 (B̃(2)B2) excited states, respectively. The recorded energy shifts indicate that in the case of He* and Ne*-H2S the autoionization dynamics depends on the features of the collision complex and is mainly driven by an effective global attraction that comes from a balance among several non covalent intermolecular interaction components. This suggests that the Penning ionization should take place, in a specific range of intermolecular distances, as we have already observed in the case of Penning ionization of water molecules [Brunetti, B. G.; Candori, P.; Falcinelli, S.; Pirani, F.; Vecchiocattivi, F. J. Chem. Phys. 2013, 139, 164305-1-164305-8].

Two-Dimensional Penning Ionization Electron Spectroscopy of Open-Shell Metallocenes: Outer Valence Ionic States of Vanadocene and Nickelocene

In order to investigate outer valence ionic states of open-shell metallocenes, we have applied two-dimensional collision-energy/electron-energy-resolved Penning ionization electron spectroscopy (2D-PIES) upon collision with metastable He*(2(3)S) excited atoms as well as a high level ab initio molecular orbital calculation (the partial third-order quasiparticle theory of the electron propagator (P3)) to ionization from neutral ground states of vanadocene ((4)A2g) and nickelocene ((3)A2g). Assignments of observed Penning ionization electron/He I ultraviolet photoelectron spectra were consistent with the P3 calculation results for ionization of α and β spin electrons except for electron correlation bands observed by PIES. Negative collision energy dependence of partial Penning ionization cross-sections (CEDPICS) indicate attractive interaction with He*(2(3)S) around the molecule. Results by model potential calculation utilizing Li(2(2)S) instead of He*(2(3)S) for interaction between He*(2(3)S) and open-shell metallocenes do not explain the strong negative CEDPICS of the bands observed in PIES.

Penning ionization electron spectroscopy of water molecules by metastable neon atoms

The Penning ionization electron spectra in metastable Ne∗(3P0,2) colliding with H2O molecules at 0.040, 0.075, 0.130, 0.200 and 0.300eV collision energies have been measured and compared with the photoelectron spectrum with Ne(I) photons. The results show the formation of the ground X̃(2B1) and the first excited state Ã(2A1) of the H2O+ product ion, with a X̃/Ã branching ratio slightly increasing with the collision energy, and with an average value of 0.29±0.03. The spectra have been analyzed in order to obtain some information and some basic features of the potential energy interaction between the two reacting particles.

ChemInform Abstract: The CO-CO Interactions in Transition-Metal Hexacarbonyls Studied by Penning Ionization Electron Spectroscopy: Cr(CO)6, Mo(CO)6 and W(CO)6.

Penning ionization electron spectra resulting from thermal collisions of He*(2 3S) metastable atoms with gaseous Cr(CO)6, Mo(CO)6, and W(CO)6 were measured to probe the CO–CO interactions. The energy splitting of the CO 5σ‐derived levels [I.P.(8a1g)−I.P.(8t1u)] was determined for the first time. Further, the spectra show that the through‐space interaction among the CO 5σ orbitals not only stabilizes the orbital energy of the CO 5σ‐derived 8a1g molecular orbital, but also gives rise to a diffuse electron distribution. The CO–CO interactions in the transition‐metal (TM) carbonyls were compared to those in the CO overlayer formed on TM surfaces.

Two-dimensional Penning ionization electron spectroscopy of CH3I and CH2I2 by He*(23S) metastable atoms

Penning ionization of iodomethane (CH3I) and diiodomethane (CH2I2) upon collision with metastable He*(23S) atoms was studied by collision-energy/electron-energy resolved two-dimensional Penning ionization electron spectroscopy (2D-PIES) over a wide range of collision energies (20 – 350 meV). Collision energy dependence of partial ionization cross sections (CEDPICS) indicates that the interaction with He*(23S) atoms around the valence molecular orbitals is attractive at low collision energies except for the only σCH molecular orbital region of iodomethane which has a repulsive character in the normal collision energy range (70 – 350 meV). Large bands at lower electron energies (3.7 – 5.5 eV) in PIES spectra were ascribed to autoionization from a transient ion-pair. The related entrance ionization channel has an attractive character. The excitation transfer, which is responsible for the I** autoionization, takes place in regions close to carbon atoms and is repulsive towards He*(23S) in the normal collision energy range. The superexcited complex of (He-CH2I2)** autoionizes via the excitation transfer occurring close to the σCI regions of the targets.

Collision-energy-resolved metastable impact electron spectroscopy of thiophene and 2,2'-bithiophene: Stereodynamics in gas phase and adsorbed layer on Ag(110)

2,2'-bithiophene in the gas phase was studied by ultraviolet photoelectron spectroscopy (UPS) and two-dimensional Penning ionization electron spectroscopy (2D-PIES) to obtain the information of stereodynamics in Penning ionization and anisotropic interaction around the ionization region. Thiophene and the 2,2'-bithiophene layer on a Ag(110) surface were investigated by two-dimensional metastable impact electron spectroscopy (2D-MIES). From the relative intensity in the UPS and PIES spectra and the collision energy dependence of partial ionization cross sections (CEDPICS) for 2,2'-bithiophene, ionization bands were assigned to π orbitals. A comparison with the CEDPICS for a gas molecule and the molecular layer on Ag(110) revealed that the attractive interaction between He*(23S) and both thiophene and 2,2-bithiophene was weak due to the formed molecular layer.

Valence ionized states of iron pentacarbonyl and η5-cyclopentadienyl cobalt dicarbonyl studied by symmetry-adapted cluster-configuration interaction calculation and collision-energy resolved Penning ionization electron spectroscopy

Valence ionized states of iron pentacarbonyl Fe(CO)(5) and eta(5)-cyclopentadienyl cobalt dicarbonyl Co(eta(5)-C(5)H(5))(CO)(2) have been studied by ultraviolet photoelectron spectroscopy, two-dimensional Penning ionization electron spectroscopy (2D-PIES), and symmetry-adapted cluster-configuration interaction calculations. Theory provided reliable assignments for the complex ionization spectra of these molecules, which have metal-carbonyl bonds. Theoretical ionization energies agreed well with experimental observations and the calculated wave functions could explain the relative intensities of PIES spectra. The collision-energy dependence of partial ionization cross sections (CEDPICS) was obtained by 2D-PIES. To interpret these CEDPICS, the interaction potentials between the molecules and a Li atom were examined in several coordinates by calculations. The relation between the slope of the CEDPICS and the electronic structure of the ionized states, such as molecular symmetry and the spatial distribution of ionizing orbitals, was analyzed. In Fe(CO)(5), an attractive interaction was obtained for the equatorial CO, while the interaction for the axial CO direction was repulsive. For Co(eta(5)-C(5)H(5))(CO)(2), the interaction potential in the direction of both Co-C-O and Co-Cp ring was attractive. These anisotropic interactions and ionizing orbital distributions consistently explain the relative slopes of the CEDPICS.

Collision-Energy-Resolved Penning Ionization Electron Spectroscopy of Glycine with He(23S) Metastable Atoms: Conformational Isomers in Collisional Ionization

Conformationally dependent ionization of the simplest amino acid, glycine, is studied by Penning ionization electron spectroscopy with velocity-resolved metastable He*(2(3)S) atoms. The observed He I ultraviolet photoelectron and Penning ionization electron spectra are reproduced by superimposed theoretical spectra, assuming thermal distributions of conformers. The conformations of amino acids are determined by analyzing the observed Penning ionization cross sections, peak shifts, and collision energy dependences of partial ionization cross sections (CEDPICS). The Penning ionization cross sections are governed by collisionally accessible exterior electron densities. When the amino and carbonyl groups are exposed to He* access, the nonbonding orbitals of N (n(N)) and O atoms (n(O)) give rise to strong bands. The observed negative peak shifts and negative CEDPICS for the n(N) and n(O) orbitals suggest the presence of attractive interactions around their electron distributions. The most attractive wells are estimated to be approximately 400 meV in the direction of the n(N) orbitals by ab initio model calculations. A conformer possessing dual hydrogen bonds contributes predominantly to the spectra.

Outer Valence Ionic States of Cr(CO)6and (η5-C5H5)Co(CO)2Observed by Two-Dimensional Penning Ionization Electron Spectroscopy

Outer valence ionic states of Cr(CO)(6) and (eta(5)-C(5)H(5))Co(CO)(2) were investigated by means of Penning ionization electron spectroscopy (PIES) upon collision with metastable He*(2(3)S) excited atoms as well as high-level ab initio molecular orbital calculations taking electron correlation effects into consideration. By the 2D measurement combining the collision-energy-resolved technique of the metastable atomic beam and electron spectroscopy, ionic-state-resolved measurement of collision energy dependence of partial ionization cross sections (CEDPICS) was carried out. Because partial Penning ionization cross sections can be connected to the spatial extent of corresponding molecular orbitals (MOs) outside the boundary surface of colliding He* atoms, different slopes of CEDPICS were related to anisotropic interaction around the MO region. The observed CEDPICS and PIES band intensity were consistent with the order of calculated ionic states.

Use of Penning Ionization Electron Spectroscopy in Plasma for Measurements of Environmental Gas Constituents

A breadboard GC detector based on Penning ionization electron spectroscopy in plasma (PIES) was investigated. The PIES detector was set up in series with a gas chromatograph and a thermal conductivity detector. Two-dimensional PIES chromatograms were recorded for carbon monoxide, carbon dioxide, and methane. The analytes were identified independently of the GC retention time, and their concentrations were measured in a range between 1 and 100 ppm. PIES spectra for methane were observed for the first time and displayed two characteristic peaks with electron energies of 7.1 and 5.4 eV. Rate coefficients for Penning ionization due to collisions between 2(3)S helium metastable atoms and analyte molecules under study were found to be k*(CO) = (0.7 +/- 0.2) x 10(-10), k*(CO2) = (1.8 +/- 0.7) x 10(-10), k*(7.1 CH4) = (4.7 +/- 0.6) x 10(-10), and k*(5.4 CH4) = (8 +/- 2) x 10(-10) cm(3)/s. The work provides the basis for the development of a portable and robust analytical platform capable of in situ real-time monitoring of greenhouse gases, with a perspective toward laboratory-on-chip realization.

Stereodynamics and Outer Valence Ionic States of Ferrocene in Collisional Ionization with a He*(23S) Metastable Atom by Two-Dimensional Penning Ionization Electron Spectroscopy

Outer valence ionic states of ferrocene were investigated by means of Penning ionization electron spectroscopy upon collision with metastable He*(2(3)S) excited atoms. By two-dimensional measurement combining electron spectroscopy and collision-energy-resolved technique of the metastable atomic beam, ionic-state-resolved measurements of collision energy dependence of partial Penning ionization cross sections (CEDPICS) were carried out. Since the partial Penning ionization cross sections can be connected with spatial extension of corresponding molecular orbitals (MOs) outside the boundary surface for the collision with He* atoms, different slope values of CEDPICS were related with stereodynamics in Penning ionization as well as anisotropic interaction around the ionization region: attractive interaction around ligand pi orbitals and repulsive interaction around ligand sigma orbtials and the metal atom. The observed negative collision energy dependence of ionization cross sections for the first ((2)E(2)') and second ((2)A(1)') ionic states was consistent with configuration interactions suggested by ab initio MO calculations [J. Chem. Phys. 2002, 117, 6533], which is due to the strong electron correlation effects beyond the one-electron MO description.

Observation of anisotropic interactions and molecular orbitals of CO upon collision with He*(23S) atoms by two-dimensional Penning ionization electron spectroscopy

By collision-energy/electron-energy-resolved 2D Penning ionization electron spectroscopy as well as by theoretical calculations of the collisional ionization dynamics, the outer shape of molecular orbitals for ionization to X(2Σ+) and A(2Π) states of CO+ was sensitively probed, and the anisotropy of the interaction between He*(23S) and CO was determined. Ionization to the B(2Σ+) state of CO+ was assigned to autoionization from superexcited states by angle-resolved electron spectroscopy and theoretical simulations.

Control of the Interchain π−π Interaction and Electron Density Distribution at the Surface of Conjugated Poly(3-hexylthiophene) Thin Films

Interchain interaction, i.e., pi-pi stacking, can benefit the carrier transport in conjugated regio-regular poly(3-hexylthiophene) (P3HT) thin films. However, the existence of the insulating side hexyl chains in the surface region may be detrimental to the charge transfer between the polymer backbone and overlayer molecules. The control of the molecular orientation in the surface region is expected to alter the distribution of the pi electron density at the surface to solve such problems, which can be achieved by controlling the solvent removal rate during solidification. The evidence that the pi-electron density distribution at the outermost surface can be controlled is demonstrated by the investigation using the powerful combination of near edge X-ray absorption fine structure spectroscopy, ultraviolet photoelectron spectroscopy, and the most surface-sensitive technique: Penning ionization electron spectroscopy. From the spectroscopic studies, it can be deduced that the slower removal rate of the solvent makes the polymer chains even at the surface have sufficient time to adopt a more nearly equilibrium structure with edge-on conformation. Thus, the side hexyl chains extend outside the surface, which buries the pi-electron density contributed from the polymer backbone. Contrarily, the quench of obtaining a thermo-equilibrium structure in the surface region due to the faster removal of the solvent residual can lead to the surface chain conformation without persisting to the strong bulk orientation preference. Therefore, the face-on conformation of the polymer chain at the surface of thin films coated with high spin coating speed facilitate the electron density of the polymer backbone exposed outside the surface. Finally, thickness dependence of the surface electronic structure of P3HT thin films is also discussed.

Surface Electronic Structures of Polythiophene Derivatives

AbstractWe report the surface electronic structures of polythiophene derivatives (including polythiophene, poly(3‐butylthiophene), poly (3‐hexylthiophene)(P3HT)) thin films observed by ultraviolet photoelectron spectroscopy and Penning ionization electron spectroscopy. He*‐impact‐surface‐modification was applied on the P3HT surface to control the distribution of the electron density.

Electronic density tailing outside π-conjugated polymer surface

Penning ionization electron spectroscopy (PIES) was adopted to examine surface electronic property of conjugated poly(3-hexylthiophene) (P3HT) aiming to detect the electronic density tailing outside a polymer surface. The electronic wave function of the highest occupied molecular orbital (HOMO) state is shielded by side hexyl chain for a P3HT film with edge-on conformation and was not detected by PIES, while it is tailing outside the polymer surface for face-on conformation and was observed clearly by PIES. The presence of HOMO electronic wave function outside the polymer surface makes it possible to form HOMO-HOMO overlapping with overlayer materials, and therefore more efficient charge transfer is expected in a heterojunction structure for device application.