Dissociative Ionization Cross Sections Research Articles

Theoretical Investigation of Electron Impact Scattering on Imidazole.

This study presents the results of electron scattering calculations on a biologically important molecule, imidazole, using the UK molecular R-matrix method. The R-matrix calculations are performed using SE, SEP, and CC models, and the resonance detected in the present SEP model is found to be in better agreement with available experimental data than previous theoretical data. The study also reports an inelastic scattering cross section, which comprises dissociative electron attachment (DEA), excitation, and ionization cross section, for the first time. The total scattering cross sections are also reported for the first time. We confirm the presence of the two well-known π* shape resonances predicted earlier experimentally. Due to the scarcity of total scattering cross section (TCS) data for imidazole, we have compared the TCS of imidazole with its isoelectronic target isoxazole and drawn important conclusions. A comparison among the resonances of imidazole with those of isoxazole helps us to conclude that electron attachment to π* molecular orbitals is a general feature displayed by these five-membered heterocyclic compounds. The comprehensive electron scattering studies presented in this work are expected to provide a deeper understanding of electron-induced biochemical processes and fill gaps in the available data. Furthermore, this study is anticipated to inspire further investigations on imidazole and other five-membered heterocyclic ring molecules, which have significant applications in medicine.

Partial Ionization Cross Sections of Tungsten Hexafluoride Due to Electron Impact

The ionization data of a neutral molecule are crucial to model the energy deposition and dissociative ionization process. We study theoretically the electron impact ionization process and report on the dissociative ionization cross sections of the tungsten hexafluoride cations invoking the modified-binary-encounter-Bethe model. In this model, the binary-encounter-Bethe model is modified by applying the transformation to the binding energies of the molecular orbitals and then normalizing the partial ionization cross sections of the cations using the branching ratios. The normalization is performed at a particular energy and ensures that the branching ratios of different fragments are summed to unity. The model yielded satisfactory results for both the singly and doubly ionized ions. The approach validates the results of Basner et al. The advantages and limitations of this model are also discussed. This work corroborates the importance of mass spectrometry data in the proper understanding of the ionization process.

Electron impact cross-sections of tetraethyl silicate

Understanding the interactions of electrons with molecules in plasma is of vital importance from both academic and technological points of view. Reliable electron collision data is required to model the electron and ion components of low-temperature and nonequilibrium plasmas. Various electron impact cross sections such as the differential, integral, momentum transfer, partial and total ionizations are reported for tetraethyl silicate (TEOS), a plasma-relevant molecule in the energy range between the ionization threshold and 5 keV. The elastic (differential, integral and momentum transfer) cross sections are obtained by invoking the molecular approach and local potential approximation within the single center expansion formalism. The dissociative ionization cross sections are reported within the binary encounter Bethe (BEB) model formalism. The elastic and ionization cross sections are summed incoherently to estimate total cross sections. A good agreement is observed between the present results and others that are available. This work validates the efficacy of the modified BEB model in computing the partial ionization cross sections.

Direct And Dissociative Ionization Cross Section Of Oxygen Molecule From Threshold To 10 Kev

Due to abundant applications of ionization in various fields of applied sciences, it’s desirable to calculate absolute ionization cross sections of various atoms or molecules. In this literature, we have calculated the absolute direct and dissociative ionization cross sections of the oxygen molecule from threshold energy to 10,000 eV by using revisited Jain-Khare semi-empirical approach. In this literature, the total direct and absolute ionization cross section data have compared with easily available experimental and/or theoretical data. The present results give a better account for the ionization cross sections up to higher incident electron energies.

Mass spectrometry of d-ribose molecules

The results of mass spectra of d-ribose molecular beam study by electron impact for the 20–70 eV energy range at the evaporation temperature 310–430 K are presented. The experiment was carried out in two stages: first the mass spectra were measured in the range of 0–200 Da at different ionization energies, then relative cross-sections of single ionization of fragment ions were investigated in the electron energy range of 5–60 eV. The measured temperature dependences show the competing character of water and oxonium cation formation processes. It is the first determination of the appearance energy (AE) for the d-ribose molecule from the threshold region of the energy dependence of the effective ionization cross section. For the most intense fragment ions in the mass spectrum, the potentials of appearance are determined at the threshold of the dissociative ionization cross sections. Schemes for the fragmentation of positive d-ribose ions are proposed.

Absolute total ionization and dissociative ionization cross sections for H+ impact on N2O within the energy range of 2–10 keV

Measurements were made for the ionization and dissociative ionization of N2O in collisions with 2–10 keV protons. Absolute cross sections were obtained employing the time of flight mass spectroscopy for the slow target molecular ions and ionic fragments. Cross sections for the formation of single and doubly charged fragments are reported.

Mass spectrometry of processes of dissociative ionization of glutamine molecules

Background : Recently the interest in the radiation-implication-study of amino acids has rapidly increased due to the fundamental importance of the molecules of amino acids. Amino acids belong to biologically relevant organic substances involved in the live organisms. They serve as building blocks of proteins and intermediates in metabolism. The chemical properties of amino acids determine the biological activity of the proteins. The latter do not only catalyze most of the reactions in living cells, they also control all cellular processes. In addition, proteins contain the necessary information needed to determine the structure and the stability of the human body. The availability of such experimental data is the basis for developing new or improving existing theoretical models. Methods : The electron-impact ionization mass-spectrometric technique was used being combined with the method of normally crossed molecular and electron beams. The experiments were carried out using a modified magnetic МИ-1201 mass-spectrometer. The mass-spectra of the above molecules have been measured together with the energy dependences of their ionization and dissociative ionization cross-sections. Results : The work represents the mass-spectra of the glutamine molecules measured at energy of ionizing electrons 70 eV. The principal mass-spectra peaks have been identified. Despite the low relative intensity of the fragment ions, the energy dependences of their yield and the ionization potentials (energies) have been measured and obtained, respectively. The absolute values of the appearance energies of the main ionic fragments of the molecules under study have been determined. Conclusions: The paper presents new data on the electron-impact fragmentation of the amino acid glutamine molecule and they are presented as being related to the formation of the ionized products due to the influence of low-energy ionizing radiation on the above molecule. A series of the produced fragments have been identified. The absolute appearance energies for some of them have been measured experimentally

Electron-impact dissociation and ionization of NO+ ions

Absolute cross sections for electron-impact ionization and dissociation of NO+ ions are reported. Simple ionization to NO2+ ion and production of singly charged N+ and O+ and doubly charged N2+ and O2+ fragments have been investigated. The animated electron-ion crossed-beam method is applied in the energy range from the respective thresholds up to 2.5 keV. The maximum of the simple ionization cross section is found to be (3.49 ± 0.07) × 10−17 cm2 at 135 eV. The total cross sections for N+ and O+ fragments at the maximum are found to be (13.9 ± 1.0) × 10−17 cm2 and (14.0 ± 1.4) × 10−17 cm2, respectively, both at an energy of 85 eV. By performing careful magnetic field scans of the detected signal, contributions of dissociative excitation and dissociative ionization to N+ and O+ production are determined separately. The cross sections for asymmetric dissociative ionization to N2+ and O2+ are found to be over one order of magnitude smaller. Distributions of the kinetic energy release to the fragments are determined for all dissociation processes.

Low energy ionization and fragmentation cross sections for [formula omitted] impact on [formula omitted] and [formula omitted

Measurements were made for ionization and dissociative ionization cross sections of O2 and N2 in collisions with 2–10keV protons. Cross sections were measured for both target gases employing the time of flight mass spectroscopy for the slow target molecular ions and ionic fragments. Measured cross sections were found to connect very well with previously measured data. Ionization was found to be dominant and 5 times higher than dissociative ionization in the case of O2 and 10 times in the case ofN2. Pronounced structure around 5keV was attributed to the transition between the initial and final states of the system as well as from quantum or classical effect involving the attractive and repulsive parts of the potential energy curves of N2 and O2. The present data add to the present available data and confirm previously measured total cross sections.

Dissociative ionization cross sections of CO2 at electron impact energy of 5 keV

The dissociative ionization of CO2 induced by 5 keV electrons in two-body and three-body dissociative channels of CO22+ and CO23+ is identified by the ion—ion coincidence- method using a momentum imaging spectrometer. The partial ionization cross sections (PICSs) of different ionic fragments are measured and the results generally agree with the calculations made by a semi-empirical approach. Furthermore, the PICSs of the dissociative channels are also obtained by carefully considering the detection efficiency of the micro-channel plates and the total transmission efficiency of the time of flight system.

Cross sections for dissociative ionization and dissociative excitation of H 2 + by single photon absorption

The photo-absorption cross sections for the dissociative ionization and dissociative excitation of H 2 + are calculated for photon polarization parallel and perpendicular to the internuclear axis. The wavefunctions for the initial and final states are prepared using the Born-Oppenheimer approximation. For dissociative ionization, the cross section and angular distribution of photo-electrons are compared with those calculated with the fixed-nuclei approximation. For dissociative excitation, the cross sections for H (N = 1∼4) productions are shown.

Fragmentation of the adenine and guanine molecules induced by electron collisions.

Secondary electron emission is the most important stage in the mechanism of radiation damage to DNA biopolymers induced by primary ionizing radiation. These secondary electrons ejected by the primary electron impacts can produce further ionizations, initiating an avalanche effect, leading to genome damage through the energy transfer from the primary objects to sensitive biomolecular targets, such as nitrogenous bases, saccharides, and other DNA and peptide components. In this work, the formation of positive and negative ions of purine bases of nucleic acids (adenine and guanine molecules) under the impact of slow electrons (from 0.1 till 200 eV) is studied by the crossed electron and molecular beams technique. The method used makes it possible to measure the molecular beam intensity and determine the total cross-sections for the formation of positive and negative ions of the studied molecules, their energy dependences, and absolute values. It is found that the maximum cross section for formation of the adenine and guanine positive ions is reached at about 90 eV energy of the electron beam and their absolute values are equal to 2.8 × 10(-15) and 3.2 × 10(-15) cm(2), respectively. The total cross section for formation of the negative ions is 6.1 × 10(-18) and 7.6 × 10(-18) cm(2) at the energy of 1.1 eV for adenine and guanine, respectively. The absolute cross-section values for the molecular ions are measured and the cross-sections of dissociative ionization are determined. Quantum chemical calculations are performed for the studied molecules, ions and fragments for interpretation of the crossed beams experiments.

Calculations of electron scattering from H2+

We have extended the convergent close-coupling method to investigate electron scattering from the vibrationally excited molecular hydrogen ion H${{}_{2}}^{+}$, within the Born-Oppenheimer approximation. Results are presented for proton-production and dissociative-ionization cross sections. The comparison with experiment is excellent across the energy range from near threshold to 1 keV.

Absolute photoionization cross-sections of selected furanic and lactonic potential biofuels

Absolute photoionization cross sections of the molecules γ-butyrolactone (GBL), γ-valerolactone (GVL), α-angelicalactone (AAL), and γ-methylene-γ-butyrolactone (GMGB), including partial ionization cross sections for dissociative ionization, are measured. The experiments are carried out using photoionization mass spectrometry (PIMS) at the Advanced Light Source, and an orthogonal extraction time-of-flight spectrometer is used for mass analysis. Photoionization of furan, 2-methyl furan (2-MF), and 2,5-dimethyl furan (2,5-DMF) is also investigated to confirm the accuracy of our measurements, which show a good agreement of the absolute partial photoionization cross sections with literature values. CBS-QB3 calculations of adiabatic ionization energies (AIE) and appearance energies (AE) agree well with the experimental results.

Absolute cross sections for dissociative electron attachment and dissociative ionization of cobalt tricarbonyl nitrosyl in the energy range from 0 eV to 140 eV

We report absolute dissociative electron attachment (DEA) and dissociative ionization (DI) cross sections for electron scattering from the focused electron beam induced deposition (FEBID) precursor Co(CO)(3)NO in the incident electron energy range from 0 to 140 eV. We find that DEA leads mainly to single carbonyl loss with a maximum cross section of 4.1 × 10(-16) cm(2), while fragmentation through DI results mainly in the formation of the bare metal cation Co(+) with a maximum cross section close to 4.6 × 10(-16) cm(2) at 70 eV. Though DEA proceeds in a narrow incident electron energy range, this energy range is found to overlap significantly with the expected energy distribution of secondary electrons (SEs) produced in FEBID. The DI process, on the other hand, is operative over a much wider energy range, but the overlap with the expected SE energy distribution, though significant, is found to be mainly in the threshold region of the individual DI processes.

Inelastic collisions of the uracil molecules with electrons

Ionization and excitation of the uracil molecules by electron impact is investigated. Production of positive ions of uracil molecules (nucleic acid base) was studied using a crossed electron and molecular beam technique. The method developed by the authors enabled the molecular beam intensity to be measured and the electron dependences and the absolute values of the total cross sections of production of both positive ions to be determined. It is shown that the total positive uracil ion production cross section reaches its maximal value of (1.0 ± 0.1) × 10(-15) cm(2) at the 95 eV electron energy. Dissociative ionization cross sections were also determined. The luminescence spectra of isolated uracil molecules in the wavelength range of 200-500 nm under the influence of slow electrons are obtained. In the spectrum, more than 20 spectral bands and lines at 100 eV electron energy are observed. It is shown that the uracil radiation spectrum is formed by the processes of molecules dissociative excitation, dissociative excitation with ionization, excitation of electronic levels of the initial molecule and molecular ion.

Scattering Angle Dependence of Double Differential Cross Sections for Dissociative Ionization of H2 by Proton Impact

We have measured double differential cross sections for dissociative ionization of H2 by 75 keV proton impact for fixed energy losses as a function scattering angle. The data exhibit an oscillating pattern with a frequency about twice as large as found earlier for non-dissociative ionization.

Gas phase low energy electron induced decomposition of the focused electron beam induced deposition (FEBID) precursor trimethyl (methylcyclopentadienyl) platinum(iv) (MeCpPtMe3)

Relative cross sections for dissociative electron attachment (DEA) and dissociative ionization (DI) of the FEBID precursor, trimethyl (methylcyclopentadienyl) platinum(iv), MeCpPtMe(3), are presented. The most pronounced DEA process is the loss of one methyl radical, while the loss of two or three methyl groups along with hydrogen is the main pathway in DI. Further fragments are formed in DEA and through DI by more complex rearrangement reactions but complete dissociation to bare Pt(-) in DEA or Pt(+) in DI is minor. The transient negative ion (TNI) formation in DEA is discussed and fragmentation mechanisms are proposed for individual processes. From the thermodynamics of the DEA processes we derive a lower limit for the electron affinity of the MeCpPtMe(2) radical (1.7 eV). Appearance energies (AE) of MeCpPtMe(3)(+) (7.7 eV) and Pt(+) (18.6 eV) formation through electron impact ionisation (EI) and through DI, respectively, are determined. Finally, the current DEA and DI results are compared and brought into context with earlier surface science studies on electron-induced decomposition of adsorbed MeCpPtMe(3) as well as gas phase and surface science studies on the FEBID precursors [Co(CO)(3)NO] and [Pt(PF(3))(4)]. These comparisons strongly indicate that DEA is an important process in the electron-induced decomposition of these molecules in FEBID.

Vibrationally resolved ionization cross sections for the ground state and electronically excited states of the hydrogen molecule

Ionization cross sections for the hydrogen molecule have been calculated by applying the classical Gryzinski theory combined with the Franck–Condon theory. It is shown that—if the reaction channels, Franck–Condon factors and Franck–Condon densities are taken into account properly—the calculated cross sections for ionization of the molecular ground state X 1 Σ g + ( v ′ = 0 ) are in almost perfect agreement with the latest and most reliable experimental results. A comprehensive database is established which includes vibrationally resolved cross sections for non-dissociative and dissociative ionization of the molecular ground state as well as for the first five non-repulsive electronically excited states in the molecule.

Electron impact dissociation of ND+: formation of D+

Absolute cross sections for electron impact dissociation of ND(+) leading to the formation of D(+) have been measured by applying the animated electron-ion beam method in the energy range from the reaction threshold up to 2.5 keV. The maximum inclusive cross section is observed to be (16.8 +/- 0.8) x 10(-17) cm(2) at the electron energy of 65.1 eV. The appearance energy for the D(+) production is measured to be (4.0 +/- 0.5) eV. Collected data are analyzed in details by means of an original procedure in order to determine separately the contributions of dissociative channels. A specific Monte Carlo modeling has been developed, which is proven to reconstruct adequately the dissociative ionization cross section. The present energy thresholds provide information about the ground and excited states of the molecular ion, as well as about the possible population of the vibrational levels. The reaction D(2)(v) + N(+) (or H(2)(v) + N(+)) is a probable source for that population and it constitutes the first step of the molecular activated processes, so the corresponding chain of reactions has to be considered to study the chemistry of plasma sources.