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We report calculations of total (and absolute) electron-impact ionization cross sections (EICSs) for the fusion-relevant diatomic molecular species BeH, BeN, BeO, WH, WBe, WN, WO, O2, and N2 by means of the Deutsch-Märk and the binary-encounter-Bethe methods in the energy range from threshold to 10 keV. In addition, we discuss an empirical scheme to estimate partial cross sections from the total ones based on reaction energetics and empirical threshold laws and explore its accuracy by assessing available experimental data on total and partial EICSs. Finally, we also report parameters obtained by fitting the calculated cross sections to an expression commonly used in fusion edge plasma modeling. [ABSTRACT FROM AUTHOR]

The smallest doubly charged coronene cluster ions reported so far, Cor152+, were produced by charge exchange between bare coronene clusters and He2+ [H. A. B. Johansson et al., Phys. Rev.A84, 043201 (2011)]. These dications are at least five times larger than the estimated Rayleigh limit, i.e., the size at which the activation barrier for charge separation vanishes. Such a large discrepancy is unheard of for doubly charged atomic or molecular clusters. Here we report the mass spectrometric observation of doubly charged coronene trimers, produced by electron ionization of helium nanodroplets doped with coronene. The observation implies that Cor32+ features a non-zero fission barrier too large to overcome under the present experimental conditions. The height of the barriers for the dimer and trimer has been estimated by means of density functional theory calculations. A sizeable barrier for the trimer has been revealed in agreement with the experimental findings. [ABSTRACT FROM AUTHOR]

In this article, the differential ionization cross-sections of the HCl molecule in the gas phase is investigated. The single differential ionization cross-section (SDCS) as a function of loss of incident electron energy and Double Differential Cross Section (DDCS) as a function of energy loss of incident electron and incident angle, is calculated. To reach exact values of differential ionization cross sections for HCl molecule, a modified semi-empirical approach of Jain and Khare is used. Partial and total absolute ionization cross-section of HCl is available but there is no data for differential ionization crosssections. So, first time, the results for single and double differential ionization cross-sections for HCl molecule is investigated. [ABSTRACT FROM AUTHOR]

Site-specific fragmentation upon 1s photoionisation of acetaldehyde has been studied using synchrotron radiation and a multi-electron-ion coincidence technique based on a magnetic bottle. Experimental evidence is presented that bond rupture occurs with highest probability in the vicinity of the initial charge localisation and possible mechanisms are discussed. We find that a significant contribution to site-specific photochemistry is made by different fragmentation patterns of individual quantum states populated at identical ionisation energies. [ABSTRACT FROM AUTHOR]

We analyzed calculated cross sections for K-, L-, and M-shell ionization by electron impact to determine the energy ranges over which these cross sections are consistent with the Bethe equation for inner-shell ionization. Our analysis was performed with K-shell ionization cross sections for 26 elements, with L-shell ionization cross sections for seven elements, L3-subshell ionization cross sections for Xe, and M-shell ionization cross sections for three elements. The validity (or otherwise) of the Bethe equation could be checked with Fano plots based on a linearized form of the Bethe equation. Our Fano plots, which display theoretical cross sections and available measured cross sections, reveal two linear regions as predicted by de Heer and Inokuti [in Electron Impact Ionization, edited by T. D. Märk and G. H. Dunn, (Springer-Verlag, Vienna, 1985), Chap. 7, pp. 232-276]. For each region, we made linear fits and determined values of the two element-specific Bethe parameters. We found systematic variations of these parameters with atomic number for both the low- and the high-energy linear regions of the Fano plots. We also determined the energy ranges over which the Bethe equation can be used. [ABSTRACT FROM AUTHOR]

This paper's objective is to create a "consistent" mean-field based Kohn-Sham (KS) density functional theory (DFT) meaning the functional should not only provide good total energy properties, but also the corresponding KS eigenvalues should be accurate approximations to the vertical ionization potentials (VIPs) of the molecule, as the latter condition attests to the viability of the exchangecorrelation potential (VXC). None of the prominently used DFT approaches show these properties: the optimized effective potential VXC based ab initio dft does. A local, range-separated hybrid potential cam-QTP-00 is introduced as the basis for a "consistent" KS DFT approach. The computed VIPs as the negative of KS eigenvalue have a mean absolute error of 0.8 eV for an extensive set of molecule's electron ionizations, including the core. Barrier heights, equilibrium geometries, and magnetic properties obtained from the potential are in good agreement with experiment. A similar accuracy with less computational efforts can be achieved by using a non-variational global hybrid variant of the QTP-00 approach. [ABSTRACT FROM AUTHOR]

We investigate the electron ionization of clusters generated in mixed Ar-water expansions. The electron energy dependent ion yields reveal the neutral cluster composition and structure: water clusters fully covered with the Ar solvation shell are formed under certain expansion conditions. The argon atoms shield the embedded (H2O)n clusters resulting in the ionization threshold above ≈15 eV for all fragments. The argon atoms also mediate more complex reactions in the clusters: e.g., the charge transfer between Ar+ and water occurs above the threshold; at higher electron energies above ∼28 eV, an excitonic transfer process between Ar+* and water opens leading to new products ArnH+ and (H2O)nH+. On the other hand, the excitonic transfer from the neutral Ar* state at lower energies is not observed although this resonant process was demonstrated previously in a photoionization experiment. Doubly charged fragments (H2O)nH22+ and (H2O)n2+ ions are observed and Intermolecular Coulomb decay (ICD) processes are invoked to explain their thresholds. The Coulomb explosion of the doubly charged cluster formed within the ICD process is prevented by the stabilization effect of the argon solvent. [ABSTRACT FROM AUTHOR]

In this paper, we present the mechanisms of ionization of a thin gold film irradiated by a high-intensity, short-pulse laser in the range of I = 10 20 − 22 W / cm 2 and the associated acceleration of multiply charged gold ions. A numerical one-dimensional simulation using an extended particle-in-cell code, which includes atomic and collisional relaxation processes, indicates that two types of acceleration, hole-boring radiation pressure acceleration (RPA) and target normal sheath acceleration (TNSA), contribute to the generation of highly charged ions with kinetic energies on the order of 10 MeV/u. In each acceleration, a longitudinal electrostatic field excited by different mechanisms dominantly ionizes atoms to higher charge states and accelerates them to the vacuum region from the rear surface, which is opposite the front surface irradiated by the laser field. The field ionization process dominantly ionizes high energy ions to the high charge state, while a large number of ions with energy < 1 MeV / u are ionized by an electron impact ionization process. In TNSA, a multiply charged ion generated at the rear surface is accelerated to the maximum energy although the ion with the highest charge state is generated at the front surface in RPA. However, the existence of contamination, such as water vapor, suppresses the ion energy of TNSA to less than that of RPA since the sheath field readily accelerates the protons and oxygen prior to the acceleration of the gold ions. Our derived theoretical scaling describes the maximum ion energy for each charge state in the cases with and without contamination using the relationship between the longitudinal electrostatic field profile near the rear surface and the classical tunnel field ionization model. [ABSTRACT FROM AUTHOR]

2,5-dimethylfuran (C6H8O) is an important fuel additive and a possible renewable liquid fuel for the future. This paper presents a recent Fourier transfer mass spectrometry study on the formation of ions from C6H8O by electron impact ionization and by ion-molecule reactions. Cross sections of the partial electron impact ionization have been measured and the pathways of major fragmentation channels of the parent ion have been examined. The kinetics of the reactions of C6H8O with selected product ions from electron impact and Ar+ have been studied. [ABSTRACT FROM AUTHOR]

The C 1s and N 1s Auger spectra of pyrimidine, 2-chloropyrimidine, and 5-bromopyrimidine have been measured in an electron impact experiment at 1000 eV. In the case of the halogen-substituted pyrimidines, also the Cl 2p and Br 3d Auger spectra have been recorded. We have thoroughly analyzed and interpreted all the Auger spectra recorded here with the aid of accurate Green’s function calculations with a large basis set. The spectra are extremely complex with thousands of states contributing and almost no single-state feature even near the double ionization threshold. Besides reproducing and explaining with great detail nearly all the main spectral features observed, the calculations have successfully unraveled the interplay among the different C 1s core hole chemical shifts in each molecule and how this affects some fingerprinting details in the composite C 1s Auger spectra. [ABSTRACT FROM AUTHOR]

Electron-ion-ion coincidence measurements of sulfur dioxide at discrete resonances near the O 1s ionization edge are reported. The spectra are analyzed using a model based upon molecular symmetry and on the geometry of the molecule. We find clear evidence for molecular alignment that can be ascribed to symmetry properties of the ground and core-excited states. Configuration interaction (CI) calculations indicate geometry changes in accord with the measured spectra. For the SO2 molecule, however, we find that the localized core hole does not produce measurable evidence for valence localization, since the transition dipole moment is not parallel to a breaking σ* O–S bond, in contrast to the case of ozone. The dissociation behavior based upon the CI calculations using symmetry-broken orbitals while fixing a localized core-hole site is found to be nearly equivalent to that using symmetry-adapted orbitals. This implies that the core-localization effect is not strong enough to localize the σ* valence orbital. [ABSTRACT FROM AUTHOR]

One-photon mass-analyzed threshold ionization (MATI) spectra for the X 2E3/2 states of CH3I+ and CD3I+ were measured using vacuum ultraviolet radiation generated by four-wave mixing in Kr. Spin-orbit density functional theory calculations at the B3LYP/aug-cc-pVTZ level and spin-orbit/Jahn-Teller calculations were made to aid vibrational assignment. Each vibrational band consisted of several peaks due to different ΔK transitions, which could be assigned by using molecular parameters determined in the previous high resolution photodissociation spectroscopic study. Possibility of generating mass-selected, vibronically selected and K-selected ion beam with decent intensity by one-photon MATI was demonstrated. The ionization energies to the X 2E3/2 states of CH3I+ and CD3I+ corrected for the rotational contribution were 9.5386±0.0006 and 9.5415±0.0006 eV, respectively. [ABSTRACT FROM AUTHOR]

Photodissociation of CH3I+ in the ground vibronic state generated by mass-analyzed threshold ionization resulted in a superb spectrum for the first excited electronic state (A 2A1) with hardly any spurious peak. Rotational structure in the spectrum could be resolved by using a single mode laser. This structure for one vibronic band, 213161, was analyzed with the assumption of Hund’s case (a) scheme both in the ground and excited electronic states. [ABSTRACT FROM AUTHOR]

Ethanol molecules were irradiated with a pair of temporally overlapping ultrashort intense laser pulses (1013–1014 W/cm2) with different colors of 400 and 800 nm, and the dissociative ionization processes have been investigated. The yield ratio of the C–O bond breaking with respect to the C–C bond breaking was varied in the range of 0.17–0.53 sensitively depending on the delay time between the two laser pulses, and the absolute value of the yield of the C–O bond breaking was found to be increased largely when the Fourier-transform limited 800 nm laser pulse overlaps the stretched 400 nm laser pulse, demonstrating an advantage of the two-color intense laser fields in controlling chemical bond breaking processes. [ABSTRACT FROM AUTHOR]

The ionization of a beam of H2 Rydberg molecules in collision with a metal surface (evaporated Au or Al) is studied. The Rydberg states are excited in an ultraviolet–vacuum ultraviolet double-resonant process and are state selected with a core rotational quantum number N+=0 or 2 and principal quantum numbers n=17–22 (N+=2) or n=41–45 (N+=0). It is found that the N+=0 states behave in a very similar manner to previous studies with atomic xenon Rydberg states, the distance of ionization from the surface scaling with n2. The N+=2 states, however, undergo a process of surface-induced rotational autoionization in which the core rotational energy transfers to the Rydberg electron. In this case the ionization distance scales approximately with ν02, the effective principal quantum number with respect to the adiabatic threshold. This process illustrates the close similarity between field ionization in the gas phase and the surface ionization process which is induced by the field due to image charges in the metal surface. The surface ionization rate is enhanced at certain specific values of the field, which is applied in the time interval between excitation and surface interaction. It is proposed here that these fields correspond to level crossings between the N+=0 and N+=2 Stark manifolds. The population of individual states of the N+=2, n=18 Stark manifold in the presence of a field shows that the surface-induced rotational autoionization is more facile for the blueshifted states, whose wave function is oriented away from the surface, than for the redshifted states. The observed processes appear to show little dependence on the chemical nature of the metallic surface, but a significant change occurs when the surface roughness becomes comparable to the Rydberg orbit dimensions. [ABSTRACT FROM AUTHOR]

This article describes the scaling of plane-wave Born cross sections for the excitation of the H2 molecule to four low-lying electronic states (B 1Σu+, C 1Πu, B′ 1Σu+, and D 1Πu) by electron impact. The same BE and BEf scaling methods used on atoms were found to be equally effective for H2 in converting Born cross sections into cross sections in good agreement with available experiments. These scaling methods are applicable only to dipole-allowed excitations. The possibility of using these scaling methods, as was done in atoms, to estimate the contribution of inner-shell excitations to the total ionization cross section via the excitation-autoionization mechanism is discussed, though this type of indirect ionization in molecules is not as common as in atoms. [ABSTRACT FROM AUTHOR]

The authors report absolute differential and integral cross section measurements for electron-impact excitation of the à 1B1 electronic state of water. This is an important channel for the production of the OH (X 2Π) radical, as well as for understanding the origin of the atmospheric Meinel [Astrophys. J. 111, 555 (1950)] bands. The incident energy range of our measurements is 20–200 eV, while the angular range of the differential cross section data is 3.5°–90°. This is the first time such data are reported in the literature and, where possible, comparison to existing theoretical work, and new scaled Born cross sections calculated as a part of the current study, is made. The scaled Born cross sections are in good agreement with the integral cross sections deduced from the experimental differential cross sections. In addition they report (experimental) generalized oscillator strength data at the incident energies of 100 and 200 eV. These data are used to derive a value for the optical oscillator strength which is found to be in excellent agreement with that from an earlier dipole (e,e) experiment and an earlier photoabsorption experiment. [ABSTRACT FROM AUTHOR]

The authors report new differential cross section measurements for electron impact excitation of the A 1Π(v′) states of carbon monoxide. The energy range is 20–200 eV. They also reanalyze the A 1Π(v′) manifold cross sections of Middleton et al. [J. Phys. B 26, 1743 (1993)] in order to provide a basis for comparison with our new vibrationally resolved differential cross sections. Excellent agreement is found between the two sets of measurements at all common energies. From 20 to 200 eV the present differential cross sections are extrapolated and integrated, and the corresponding integral excitation cross sections determined. New scaled Born integral cross sections, calculated as a part of the present study, are compared against these experimental integral cross sections, with excellent agreement being found for all the A 1Π(v′=0–7)←X 1Σg+(v″=0) transitions. In addition our scaled Born integral cross sections are found to be in excellent agreement between 300 and 1500 eV with those derived from the previous experiments of Lassettre and Skerbele [J. Chem. Phys. 54, 1597 (1971)] and of Zhong et al. [Phys. Rev. A 55, 1799 (1997)] and from near threshold to 15 eV with those derived from Zobel et al. [J. Phys. B 29, 813 (1996)] and Zetner et al. (J. Phys. B 31, 2395 (1998)]. [ABSTRACT FROM AUTHOR]

The pulsed field ionization–zero kinetic energy photoelectron technique has been used to observe the low-lying energy levels of UO+. Rotationally resolved spectra were recorded for the ground state and the first nine electronically excited states. Extensive vibrational progressions were characterized. Ω+ assignments were unambiguously determined from the first rotational lines identified in each vibronic band. Term energies, vibrational frequencies, and anharmonicity constants for low-lying energy levels of UO+ are reported. In addition, accurate values for the ionization energies for UO [48643.8(2) cm-1] and U [49957.6(2) cm-1] were determined. The pattern of low-lying electronic states for UO+ indicates that they originate from the U3+(5f3)O2- configuration, where the uranium ion-centered interactions between the 5f electrons are significantly stronger than interactions with the intramolecular electric field. The latter lifts the degeneracy of U3+ ion-core states, but the atomic angular momentum quantum numbers remain reasonably well defined. [ABSTRACT FROM AUTHOR]

A restricted-open-shell model chemistry based on the complete basis set-quadratic Becke3 (CBS-QB3) model is formulated and denoted ROCBS-QB3. As the name implies, this method uses spin-restricted wave functions, both for the direct calculations of the various components of the electronic energy and for extrapolating the correlation energy to the complete-basis-set limit. These modifications eliminate the need for empirical corrections that are incorporated in standard CBS-QB3 to compensate for spin contamination when spin-unrestricted wave functions are used. We employ an initial test set of 19 severely spin-contaminated species including doublet radicals and both singlet and triplet biradicals. The mean absolute deviation (MAD) from experiment for the new ROCBS-QB3 model (3.6±1.5 kJ mol-1) is slightly smaller than that of the standard unrestricted CBS-QB3 version (4.8±1.5 kJ mol-1) and substantially smaller than the MAD for the unrestricted CBS-QB3 before inclusion of the spin correction (16.1±1.5 kJ mol-1). However, when applied to calculate the heats of formation at 298 K for the moderately spin-contaminated radicals in the G2/97 test set, ROCBS-QB3 does not perform quite as well as the standard unrestricted CBS-QB3, with a MAD from experiment of 3.8±1.6 kJ mol-1 (compared with 2.9±1.6 kJ mol-1 for standard CBS-QB3). ROCBS-QB3 performs marginally better than standard CBS-QB3 for the G2/97 set of ionization energies with a MAD of 4.1±0.1 kJ mol-1 (compared with 4.4±0.1 kJ mol-1) and electron affinities with a MAD of 3.9±0.2 kJ mol-1 (compared with 4.3±0.2 kJ mol-1), but the differences in MAD values are comparable to the experimental uncertainties. Our overall conclusion is that ROCBS-QB3 eliminates the spin correction in standard CBS-QB3 with no loss in accuracy. [ABSTRACT FROM AUTHOR]

Using a Nier-type electron impact ion source in combination with a double focusing two sector field mass spectrometer, partial cross sections for electron impact ionization of acetylene are measured for electron energies up to 1000 eV. Discrimination factors for ions are determined using the deflection field method in combination with a three-dimensional ion trajectory simulation of ions produced in the ion source. Analysis of the ion yield curves obtained by scanning the deflectors allows the assignment of ions with the same mass-to-charge ratio to specific production channels on the basis of their different kinetic energy distributions. This analysis also allows to determine, besides kinetic energy distributions of fragment ions, partial cross sections differential in kinetic energy. Moreover a charge separation reaction, the Coulomb explosion of the doubly charged parent ions C2H2++ into the fragment ions C2H+ and H+, is investigated and its mean kinetic energy release (=3.88 eV) is deduced. [ABSTRACT FROM AUTHOR]

By the use of invariance principles a procedure to characterize thin films using an electron microprobe is reported. Experimental quantities such as the detected intensities and electron fluxes in the boundaries of a solid system are described by the invariant embedding method. In addition, differential equations are given for the probabilities of the different “destinations” of the electrons inside a solid as functions of the sample thickness. The procedure reported here makes it possible to perform microanalysis without the need of making approaches to estimate the ionization distribution function. The decaying in the energy of the electrons is described by a state ladder model. A few but usual cases for which this method gives fairly good agreement with experimental results are reported. The method seems to be promising to obtain procedures in microanalysis. [ABSTRACT FROM AUTHOR]

We have investigated the ionization threshold behavior of small helium cluster ions (cluster size n=2-10) formed via electron-impact ionization of neutral helium droplets and derive appearance energies for mass-selected cluster ions using a nonlinear least-square-fitting procedure. Moreover, we report magic numbers in the mass spectrum observed at the electron energy of 70 eV. The apparatus used for the present measurements is a hemispherical electron monochromator combined with a quadrupole mass spectrometer. Our experiment demonstrates that helium clusters are not only exclusively formed via direct ionization above the atomic ionization potential but also indirectly via autoionizing Rydberg states. The present results are compared with previous electron-impact and photoionization results. [ABSTRACT FROM AUTHOR]

The electron-impact ionization coefficient (α) in In0.53Ga0.47As increases with temperature at electric fields below 200 kV/cm, in contrast to most crystalline semiconductors. It exhibits conventional negative temperature dependence at higher fields. A four-valley analytical band Monte Carlo model is used to study this anomalous behavior. The simulations show that both alloy scattering and the temperature dependence of the impact ionization threshold energy contribute to the temperature dependence of α. At low fields, we find that most ionization events occur in the first conduction band causing an increase of α with temperature in In0.53Ga0.47As. At high fields, α decreases with temperature again because of the reduced hot-electron population in the second conduction band. [ABSTRACT FROM AUTHOR]

In this paper, we present a theoretical approach to calculate differential and total ionization cross sections of polyatomic molecules by fast electron impact. More exactly, we have studied the ionization of ammonia (NH3) and methane (CH4) molecules, and previous results concerning the H2O molecule ionization are reported for comparison. The calculations are performed in the distorted wave Born approximation without exchange by employing the independent electron model. The molecular target wave functions are described by linear combinations of atomic orbitals. To describe the interaction between the inactive target electrons and the slow ejected electron, we have introduced a distortion via an effective potential calculated for each molecular orbital. The present theoretical calculations agree well with a large set of existing experimental data in terms of multiple differential and total cross sections. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Electrical breakdown in homogeneous liquid water for an ∼100 ns voltage pulse is analyzed. It is shown that electron-impact ionization is not likely to be important and could only be operative for low-density situations or possibly under optical excitation. Simulation results also indicate that field ionization of liquid water can lead to a liquid breakdown provided the ionization energies were very low in the order of 2.3 eV. Under such conditions, an electric-field collapse at the anode and plasma propagation toward the cathode, with minimal physical charge transport, is predicted. However, the low, unphysical ionization energies necessary for matching the observed current and experimental breakdown delays of ∼70 ns precludes this mechanism. Also, an ionization within the liquid cannot explain the polarity dependence nor the stochastic-dendritic optical emission structures seen experimentally. It is argued here that electron-impact ionization within randomly located microbubbles is most likely to be responsible for the collective liquid breakdown behaviors. [ABSTRACT FROM AUTHOR]

An ab initio investigation of the potential energy surfaces and vibrational energies and wave functions of the anion, neutral, and cation Cu(H2O) complexes is presented. The equilibrium geometries and harmonic frequencies of the three charge states of Cu(H2O) are calculated at the MP2 level of theory. CCSD(T) calculations predict a vertical electron detachment energy for the anion complex of 1.65 eV and a vertical ionization potential for the neutral complex of 6.27 eV. Potential energy surfaces are calculated for the three charge states of the copper-water complexes. These potential energy surfaces are used in variational calculations of the vibrational wave functions and energies and from these, the dissociation energies D0 of the anion, neutral, and cation charge states of Cu(H2O) are predicted to be 0.39, 0.16, and 1.74 eV, respectively. In addition, the vertical excitation energies, that correspond to the 4 2P←4 2S transition of the copper atom, and ionization potentials of the neutral Cu(H2O) are calculated over a range of Cu(H2O) configurations. In hydrogen-bonded, Cu-HOH configurations, the vertical excitation and ionization energies are blueshifted with respect to the corresponding values for atomic copper, and in Cu-OH2 configurations where the copper atom is located near the oxygen end of water, both quantities are redshifted. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Absolute partial and total cross sections for electron-impact ionization of CCl4 and CCl2F2 are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ion species are collected with equal efficiency irrespective of their initial kinetic energies. Data are presented for production of CCl3+, CCl2+, CCl+, C+, Cl2+, and CCl32+ from CCl4; and for production of CCl2F+, CClF2+, CClF+, (CCl++CF2+), Cl+, CF+, F+, and C+ from CCl2F2. Data are also reported for formation of (CCl2+,Cl+) and (CCl+,Cl+) ion pairs from CCl4. The total cross section for each target is obtained as the sum of the partial cross sections. The overall uncertainty in the absolute cross sections for most of the singly charged ions is ±5–7 %. The present partial cross sections for lighter fragment ions are found to be considerably greater than had been previously reported but the most recent total cross section measurements agree well with those reported here. Neither the binary-encounter-Bethe theory nor the Deutsch–Märk theory reproduces the experimental cross sections correctly for both targets. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Absolute partial and total cross sections for electron-impact ionization of CCl4 and CCl2F2 are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ion species are collected with equal efficiency irrespective of their initial kinetic energies. Data are presented for production of CCl3+, CCl2+, CCl+, C+, Cl2+, and CCl32+ from CCl4; and for production of CCl2F+, CClF2+, CClF+, (CCl++CF2+), Cl+, CF+, F+, and C+ from CCl2F2. Data are also reported for formation of (CCl2+,Cl+) and (CCl+,Cl+) ion pairs from CCl4. The total cross section for each target is obtained as the sum of the partial cross sections. The overall uncertainty in the absolute cross sections for most of the singly charged ions is ±5–7 %. The present partial cross sections for lighter fragment ions are found to be considerably greater than had been previously reported but the most recent total cross section measurements agree well with those reported here. Neither the binary-encounter-Bethe theory nor the Deutsch–Märk theory reproduces the experimental cross sections correctly for both targets. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Single and double differential ionization cross sections for the production of ions resulting from dissociative, single and double ionization of SF[sub 6] by electron impact have been calculated using a semiempirical formulation based on the Jain–Khare approach. In addition, triple differential cross sections have been obtained for some of the doubly charged fragment ions at an incident electron energy of 100, 150, and 200 eV, respectively, and a fixed scattering angle of 30°. As no previous data seem to exist for differential cross sections we have derived from these differential cross sections corresponding partial and total ionization cross sections from threshold up to 900 eV and compared those with the available theoretical and experimental data. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A set of photodissociation experiments and simulations of hydrogen iodide (HI) on Ar[sub n] clusters, with an average size =139, has been carried out for different laser polarizations. The doped clusters are prepared by a pick-up process. The HI molecule is then photodissociated by a UV laser pulse and the outgoing H fragment is ionized by resonance enhanced multiphoton ionization in a (2+1) excitation scheme within the same laser pulse at the wavelength of 243 nm. The measured time-of-flight spectra are transformed into hydrogen kinetic energy distributions. They exhibit a strong fraction of caged H atoms at zero-kinetic energy and peaks at the unperturbed cage exit for both spin–orbit channels nearly independent of the polarization. At this dissociation wavelength, the bare HI molecule exhibits a strict state separation, with a parallel transition to the spin–orbit excited state and perpendicular transitions to the ground state. The experimental results have been reproduced using molecular simulation techniques. Classical molecular dynamics was used to estimate the HI dopant distribution after the pick-up procedure. Subsequently, quasi-classical molecular dynamics (Wigner trajectories approach) has been applied for the photodissociation dynamics. The following main results have been obtained: (i) The HI dopant lands on the surface of the argon cluster during the pick-up process, (ii) zero-point energy plays a dominant role for the hydrogen orientation in the ground state of HI–Ar[sub n] surface clusters, qualitatively changing the result of the photodissociation experiment upon increasing the number of argon atoms, and, finally, (iii) the scattering of hydrogen atoms from the cage which originate from different dissociation states seriously affects the experimentally measured kinetic energy distributions. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Electron impact ionization of the chlorodifluoromethane molecule is studied using crossed beams of high-resolution electrons and an effusive molecular beam of CHF[sub 2]Cl. Ionization energies (IEs) for many positive ions from CHF[sub 2]Cl (CHF[sub 2]Cl[sup +],CF[sub 2]Cl[sup +],CHFCl[sup +],CFCl[sup +],CHF[sub 2][sup +],CF[sub 2][sup +],HCl[sup +],Cl[sup +],CF[sup +],CH[sup +],F[sup +] C[sup +]) are determined from a careful examination of the threshold behavior of the ionization cross sections. Reaction pathways for the dissociative ionization products are suggested using known thermodynamic quantities. Surprisingly, it is observed that the ionization threshold for the parent positive ion IE(CHF[sub 2]Cl[sup +]/CHF[sub 2]Cl)=12.50(±0.05) eV lies above that for the fragment ions CHF[sub 2][sup +], CHFCl[sup +], and CF[sup +] [IE(CHF[sub 2][sup +]/CHF[sub 2]Cl)=12.24(±0.03) eV, IE(CHFCl[sup +]/CHF[sub 2]Cl)=12.3(±0.05) eV, and IE(CF[sup +]/CHF[sub 2]Cl)=11.5(±0.1) eV]. Experiments using a three sector field BEE mass spectrometer provide evidence for the existence of two states of the parent CHF[sub 2]Cl[sup +] ion, one exhibiting a short lifetime of about 2 μs and another parent ion state which appears to be stable on the time scale of the experiment (>20 μs) with an IE of 12.50 eV. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Mono-, di- and trinuclear complexes of Fe(III), Co(II), Ni(II), and Cu(II) ions with Bis-N,N'(salicylidene)-1,3-diaminopropane (LH2), Bis-N,N'(salicylidene)-2,2'-dimethyl-1,3-diaminopropane (LDMH2), N(salicylidene)-2-hydroxyaniline (SAP), and Tris-N,N',N"(salicylidene)-2,2',2"-aminoethylamine (Trensal) were prepared and ionized with 30-110 eV electrons in direct inlet (DI). Compounds with metal-oxygen covalent bonds were observed to give molecular peaks, whereas polynuclear complexes containing coordinative bonds did not have such peaks. It was concluded that the coordinative bonds were dissociated by electron impact (EI). The thermogravimetric analysis reveals that the molecular peak observed for the mononuclear complexes which are stable up to 300 °C is also the base peak. The peaks obtained for the di- and trinuclear complexes that decomposed at these temperatures could not be observed as a molecular signal. The resulting fragments were evaluated and compared with the literature data. [ABSTRACT FROM AUTHOR]

This paper represents a contribution toward finding a complete set of electron collision cross sections for the methane molecule by revising all of the collision cross sections and adding the partial collision cross sections data relating to dissociation by electron impact. For the latter, there are no available measurements data for each channel of dissociation and no validated recommended data for use in the modeling, although these data are very important in order to determine different species in a methane plasma. The rate coefficients of the partial dissociative collisions into neutrals and the partial ionization collisions are also calculated, and when fitted, these can be used as input for fluid models. This paper is concluded by the validation of our set of data through a comparison between the transport coefficients calculated by using our data and the measurements of the transport coefficients that already exist in the literature. [ABSTRACT FROM AUTHOR]

Reports on the absolute partial cross sections for electron impact ionization of CH(sub 4) from threshold to 1000 eV. Overall uncertainty in the absolute cross-section values for singly charged parent ions; Mass analysis of product ions using a time-of-flight mass spectrometer and detection of the ions through a position-sensitive detector.

Electron impact ionization of C60 and C70 has been studied as a function of electron energy in the threshold region using a crossed molecular beam/electron beam double focusing sector field mass spectrometer system. Appearance energies have been determined (using a special threshold extrapolating procedure) for Cz+60-2m and Cz+70-2m ions with z ranging from 1 to 4 and m from 0 to 4, respectively. Whereas the different charge states of the parent ions of C60 and C70 have the same appearance energies within the experimental error bars, the fragment ions of C70 show slightly higher values than their C60 counterparts due to an increased kinetic shift. The presently deduced ionization energies for the C60 parent ions are in excellent agreement with previously reported reliable data for Cz+60 ions (previous data are available only up to z is 3). In contrast, these experimental values disagree strongly with a theoretical calculation by Yannouleas and Landman predicting an approximately linear dependence of the ionization energy on the charge state z, i.e., the experimental values deviate strongly from linearity with increasing charge. [ABSTRACT FROM AUTHOR]

Presents information on a study that extracted the electron impact ionization coefficient in bulk silicon using a method that is applicable for the low-electric fields. Determination of the electron ionization coefficient; Reason for the importance of impact ionization in semiconductors; Approach used to improve sensitivity of the impact ionization current measurements.

Highlights • Atomic structure data of tungsten ion, W 44 + , have been computed using different methods. • Electron impact excitations and cross sections of W 44 + are performed using R-matrix method. • Ionization cross sections by electron impact are calculated and presented in the current work. Abstract Atomic structure data, electron impact excitations and ionization cross sections of tungsten ions, W 44 + , have been calculated using the multi-configuration Dirac–Fock and R-matrix methods for a set of configurations consists of 3 d 104 s 2, 3 d 104 s 4 l , and 3 d 104 p 4 l. A set of configuration state functions (CSFs) with doubly excitations up to 5 l orbitals have been included within the calculations of energy levels and transition probabilities. As well as, 4-electron excitation to 4 l -levels and 3-electron to 5 l -levels have been involved in the computation process. R-matrix calculations of collision strength and cross section have been executed for the intercombination transitions between 3d104s2, 3d104s4p, 3d104s4d, and 3d104s4f at different angular momenta using DARC code. Resonance collision strengths have been observed at low energy of incident electron in the range of ∼ 6 – 40 Ryd, however, the strong lines are limited to 6–25 Ryd. For cross section of various transitions, resonances arising from these transitions are observed at low-electron energies in the range of 6–25 Ryd. To estimate the accuracies of calculated energy levels and transition probabilities, comparisons between experimental observations and theoretical calculations are presented. The convergence between different methods for collision strengths and cross sections are observed. Different calculations of electron impact ionization cross section of the present ion in the collision energy range of 100–1000 Ryd are evaluated. [ABSTRACT FROM AUTHOR]

Gas chromatography (GC) coupled with electron ionization (EI) mass spectrometry (MS) is a well-established technique for the analysis of volatile and semi-volatile compounds. The main advantage is the highly repeatable fragmentation of the compounds into the ion source, generating intense and diagnostic fragmentation when the ionization is performed at 70 eV; this is considered the standard ionization condition and has been used for creating many established databases, which are of great support in the analyte identification process. However, such an intense fragmentation often causes the loss of the molecular ion or more diagnostic ions, which can be detrimental for the identification of homologous series or isomers, as for instance fatty acids. To obtain this information chemical or soft ionization can be used, but dedicated ion sources and conditions are required. In this work, we explored different ionization voltages in GC-EI-MS to preserve the intensity of the molecular ion using a conventional quadrupole MS. Twenty, 30, 50, and 70 eV were tested using a mixture of fatty acid methyl esters standards. Intensity and repeatability of the most informative ions were compared. Twenty and 70 eV were then used to analyze the fatty acid composition of six different strains of mycobacteria. Two approaches were used for elaborating the data: (1) a single average spectrum of the entire chromatogram was derived, which can be considered (in terms of concept) as a direct EI-MS analysis; (2) the actual chromatographic separation of the compounds was considered after automatic alignment. The results obtained are discussed herein.ᅟ [ABSTRACT FROM AUTHOR]

The results of optical emission spectroscopy experiments probing the cold electron population of a 14 GHz Electron Cyclotron Resonance Ion Source (ECRIS) are reported. The study has been conducted with a high resolution spectrometer and data acquisition setup developed specifically for the diagnostics of weak emission line characteristic to ECRIS plasmas. The optical emission lines of low charge state ions and neutral atoms of neon have been measured and analyzed with the line-ratio method. The aforementioned electron population temperature of the cold electron population (Te < 100 eV) is determined for Maxwell-Boltzmann and Druyvesteyn energy distributions to demonstrate the applicability of the method. The temperature was found to change significantly when the extraction voltage of the ion source is turned on/off. In the case of the Maxwellian distribution, the temperature of the cold electron population is 20 ± 10 eV when the extraction voltage is off and 40 ± 10 eV when it is on. The optical emission measurements revealed that the extraction voltage also affects both neutral and ion densities. Based on the rate coefficient analysis with the aforementioned temperatures, switching the extraction voltage off decreases the rate coefficient of neutral to 1+ ionization to 42% and 1+ to 2+ ionization to 24% of the original. This suggests that switching the extraction voltage on favors ionization to charge states ≥2+ and, thus, the charge state distributions of ECRIS plasmas are probably different with the extraction voltage on/off. It is therefore concluded that diagnostics results of ECRIS plasmas obtained without the extraction voltage are not depicting the plasma conditions in normal ECRIS operation. [ABSTRACT FROM AUTHOR]

In the present work, K-shell ionization cross-sections of Chlorine and Argon due to alpha impact have been calculated through the Binary Encounter Approximation model. The effects of Coulomb deflection of the projectile under the influence of target nucleusand increase in binding energy of the target electron because of presence of the projectile inside K- shell of the target have been incorporated.The cross-sections have been averaged over Hartree-Fock momentum distribution for the target electron. The calculated cross-sections have been found in satisfactory agreement with the available experimental values and other calculated results. [ABSTRACT FROM AUTHOR]

The partial and total ionization cross sections for N 2 in gas phase by electron impact in a wide energy range have been measured by ion imaging mass spectrometer. The results are put on an absolute scale by normalizing the data of N 2 + to that of Ar + from N 2 –Ar mixture target. The overall errors are evaluated by considering various kinds of uncertainties. Comparisons are made with the previous measurements. [ABSTRACT FROM AUTHOR]

The theoretical Khare model modified by Y Kumar et al. [J. At. Mol. Sci. (2012)], has been used to calculate the total cross sections for K-shell ionization of two targets, chromium, and cobalt, (i.e., Cr & Co) due to electron impact at incident electron kinetic energy from ionization threshold energy to 1 GeV. This method is based on plane wave Born approximation. The present model requires only two atomic parameters, ionization energy, and atomic number. The calculated cross sections have been compared with the available experimental data and other theoretical cross sections. The present calculated cross sections are in excellent agreement with measured by Liovet et al. [J. Phys.B 33, 2000] and Hoffmann et al. [Z. Phys. Rev. A 22, 1980] for Cr. A good agreement is found between the present calculations and measured An et al. [Chin. Phy. Lett. 18, 2001] and Se et al. [Phys. Lett. 29, 1974]. [ABSTRACT FROM AUTHOR]

Electronic structure calculations based on a density-functional approach have been performed for P, As, B, and Al subsitutional dopants near the Si(001)-oxide interface. The structures are geometrically optimized for each charge state. P and As geometries show a strong distortion when neutral, and regain tetrahedral local bonding when ionized. This geometry change creates an activation barrier for the release of the electron. Distorted neutral dopants may react with hydrogen during the forming gas interface passivation. In contrast, B and Al show tetrahedral bonding for all charge states. All four neutral dopants show substantial energy gain upon formation of dimer complexes near the interface. Neutral B is significantly more stable when bonded to two O atoms at the interface, while neutral P is more stable bonded to four Si atoms adjacent to the interface. [ABSTRACT FROM AUTHOR]

A special xenon matrix detector has been used to study the production of S(¹S) following controlled electron impact on thiophosgene (Cl2CS) targets over an electron energy range from threshold to 400 eV. Time-of-flight spectroscopy has been used to measure S(¹S) fragment kinetic energies. Fragments with energies in excess of 1 eV have been observed. The absolute cross section for S(¹S) production reaches a maximum of [1.05±0.35]x 1018 cm² at approximately 125 eV impact energy. Two different fragmentation processes, involving triplet and singlct excited states of the parent Cl2CS molecule, have been identified. [ABSTRACT FROM AUTHOR]

The perpendicular plane ionization results of (e, 2e) triple differential cross sections (TDCS) for the Kr (4p) atoms are reported at the incident electron energies 2 eV–50 eV above ionization potential. Modified distorted wave Born approximation formalism has been employed to calculate the TDCS. The results of our calculations have been compared with the measurements of Nixon et al. and it is observed that there are certain discrepancies between theoretical and experimental results which indicate that further theoretical efforts are required to understand the cross section trends of krypton atoms in the perpendicular plane ionization. [ABSTRACT FROM AUTHOR]

Cross-sections for electron collisions with the 2-methyl-1-buten-3-yne [H 2 C C(CH 3 )C CH] molecule were measured and calculated. Absolute grand -total electron-scattering cross-section (TCS) was taken at impact energies from 0.6 to 300 eV in the linear electron-transmission experiment. The TCS energy dependence for the electron–C 5 H 6 collision has two prominent enhancements separated with a deep minimum located near 1.8 eV. In addition, in the low-energy TCS function two noteworthy features occur: (i) near 1 eV, a change in a slope on rapidly declining side of the TCS curve; (ii) between 2 and 5 eV, a distinct hump superimposed on the opposite, rising part of the curve. To search for the origin of these features in the TCS curve for C 5 H 6 , the comparison was made with results of the electron-scattering studies for selected hydrocarbon molecules. These features were attributed to the formation of short-living negative ions (resonant states). Elastic (ECS) and ionization (ICS) cross-sections for C 5 H 6 and C 4 H 2 (1,3-butadiyne) were computed up to 3 keV by means of the additivity rule (AR) approximation and the binary-encounter-Bethe (BEB) approach, respectively. For the C 5 H 6 molecule, the sum ECS + ICS is in good agreement with the experimental TCS for energies above about 40 eV. [ABSTRACT FROM AUTHOR]

Rationale The total or relative cross-sections for the ionization of polyatomic molecules by electron ionization are essential data in a wide range of applications. In addition to the total ionization cross-sections, relative ionization cross-sections are sometimes also required. Accurate values of electron ionization cross-sections of high-temperature vapor species are of importance in mass spectrometric investigations. So the need for experimental ionization cross-section data for high-temperature vapor species is vital. Methods Measurements were performed by high-temperature Knudsen effusion mass spectrometry with a MS-1301 mass spectrometer. Vaporization was carried out using molybdenum or tungsten effusion cells containing samples of pure Au and CeO2. The vapor compositions over the CeO2-Mo and CeO2-W systems were determined by Knudsen effusion mass spectrometry. The method of ion currents comparison was used to measure partial pressures. The enthalpies of the reactions under study were calculated using the third law procedure. Results The standard formation enthalpies of cerium molybdates and tungstates were determined from the relative ionization cross-sections of molybdenum, tungstate, cerium, and cerium salts. Cross-sections were calculated by different methods: simple adding atomic cross-sections with correction factor, using known ratios of complex ions, adding oxide cross sections. The traditional approach to determination of ionization cross-sections exploiting the values of atomic cross-sections and the additivity rules as well as literature experimental data was used. Conclusions The enthalpies of formation of gaseous cerium molybdates and tungstates were evaluated by measurements of the reaction enthalpies for several independent reactions. The best agreement was obtained with the data from the analysis of experimentally determined relative ionization cross-sections, and using ionization cross-sections of polyatomic molecules recommended by Drowart et al. The widely used additivity method, in spite of the additional corrections introduced, gives the worst convergence of the values under consideration. [ABSTRACT FROM AUTHOR]

Absolute double differential cross sections (DDCS) of secondary electrons emitted in ionization of O by fast electrons have been measured for different emission angles. Theoretical calculations of atomic DDCS were obtained using the first Born approximation with an asymptotic charge of Z = 1. The measured molecular DDCS were divided by twice the theoretical atomic DDCS to detect the presence of interference effects which was the aim of the experiment. The experimental to theoretical DDCS ratios showed clear signature of first order interference oscillation for all emission angles. The ratios were fitted by a first order Cohen-Fano type model. The variation of the oscillation amplitudes as a function of the electron emission angle showed a parabolic behaviour which goes through a minimum at 90°. The single differential and total ionization cross sections have also been deduced, besides the KLL Auger cross sections. In order to make a comparative study, we have discussed these results along with our recent experimental data obtained for N molecule. Graphical abstract: [ABSTRACT FROM AUTHOR]