Negative Ion States Research Articles

Studies of negative ion formation in fluoroethers and fluorosulphides using low-energy (≤10 eV) electron beam and electron swarm techniques

The attachment of low-energy (≤10 eV) electrons to four fluoroethers (CF3OCF3, CF3OCF2H, CF2HOCF2H and CF3OCH3) and two fluorosulphides (CF3SCF3 and CF3SCH3) has been studied using a time-of-flight mass spectrometer (TOFMS) and a high pressure electron swarm technique. The relative cross sections as a function of incident electron energy for all observed anions were measured by employing the former, and the total absolute electron attachment rate constants were measured by employing the latter technique. All six molecules were found to attach electrons dissociatively. The types and relative intensities of the fragment anions depend strongly on the number and relative positions of the F atoms in the molecule and on the presence of O or S atoms in the molecule. The fluorosulphides attach lower energy electrons than do the fluoroethers. The magnitude of the total electron attachment rate constants increases with increasing number of F atoms in the molecule. The observed negative ions (in decreasing order of intensity) and the positions of the peak intensities (given in parentheses in eV) are: F−(5.3) and CF3O−(4.8) from CF3OCF3; CF3O−(3.7), F−(5.7), HF−2(6.1), CFO−(5.9), and CF−3(6.7) from CF3OCF2H; CF3O−(3.0), HF−2(4.7), F−(5.0), and CFO−(4.9) from CF2HOCF2H; F−(6.7) from CF3OCH3; CF3S−(0.6) and F−(3.8) from CF3SCF3; CF3S−(∼0.0) from CF3SCH3. Energetic considerations were employed to identify possible fragmentation mechanisms of the negative ion states (NISs) leading to the production of the observed fragment negative ions and to deduce values for the electron affinities of the radicals CF3O and CF3S. CNDO/2 and MNDO molecular orbital calculations were performed on all six molecules investigated in an effort to rationalize the types, relative intensities, and positions of the maxima in the cross sections of the observed anions.

ChemInform Abstract: ELECTRON TRANSMISSION STUDY OF THE NEGATIVE ION STATES OF P‐BENZOQUINONE, BENZALDEHYDE, AND RELATED MOLECULES

Chemischer InformationsdienstVolume 15, Issue 46 Physical Organic Chemistry ChemInform Abstract: ELECTRON TRANSMISSION STUDY OF THE NEGATIVE ION STATES OF P-BENZOQUINONE, BENZALDEHYDE, AND RELATED MOLECULES A. MODELLI, A. MODELLISearch for more papers by this authorP. D. BURROW, P. D. BURROWSearch for more papers by this author A. MODELLI, A. MODELLISearch for more papers by this authorP. D. BURROW, P. D. BURROWSearch for more papers by this author First published: November 13, 1984 https://doi.org/10.1002/chin.198446040AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume15, Issue46November 13, 1984 RelatedInformation

Absolute calibration of arbitrary total cross sections for electron impact excitation of Xe metastable states in the near-threshold region

A comparison of the arbitrary cross sections for electron impact excitation of Xe metastable states obtained by Buckmann et al. (1983) with the afterglow results for quenching rate constants makes the calibration in absolute units of the excitation cross section possible. It is also shown that the resonance capture of the thermal electron by the metastable atom in a temporary negative ion state, followed by a decay to the ground state is an essential mechanism for de-excitation of the rare gas metastables. This quenching channel prevails over the conventional channel with a 1/V energy dependence for the Xe metastable atoms. The relation to a similar model for a decay of excimer molecules, is discussed.

Aspects of nuclear dynamics in short-lived negative ion states

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAspects of nuclear dynamics in short-lived negative ion statesW. Domcke, M. Berman, H. Estrada, C. Muendel, and L. S. CederbaumCite this: J. Phys. Chem. 1984, 88, 21, 4862–4867Publication Date (Print):October 1, 1984Publication History Published online1 May 2002Published inissue 1 October 1984https://doi.org/10.1021/j150665a012RIGHTS & PERMISSIONSArticle Views47Altmetric-Citations19LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (729 KB) Get e-Alerts

New electron states of negative ions in semiconductors

A theory is presented of a new class of localised states which are stabilised by enhanced correlation effects peculiar to the electronic structure of weakly-bonded defects in covalent semiconductors. A simple model of the correlation effect is employed and it is shown that it yields a consistent description of binding to N in GaP x As 1- x .

Electron transmission study of the negative ion states of p-benzoquinone, benzaldehyde, and related molecules

Par cette methode avec des electrons de 0-6 eV, localisation des resonances de forme en phase gazeuse de p-benzoquinone et de ses derives dimethyl-2,6 et di-t-butyl-2,6, d'acetophenone, de benzaldehydes p-substitues, de cyclohexanone et cyclohexene-2one-1. Ordre des orbitales normalement vacantes

Trends in temporary negative ion states in linear and cyclic alkenes

Transmission functions and hence electron affinities of linear- (ethylene to 1-hexene) and cis-cyclo-alkenes (5- to 8-membered rings) are measured by a 127° electron-transmission spectrometer. Comparison is made between reported shifts in electron affinities and existing values of ionization potentials.

Observation of Dipole-Bound States of Negative Ions

High-resolution threshold photodetachment of ${\mathrm{H}}_{2}$C-CH${\mathrm{O}}^{\ensuremath{-}}$ has resulted in the observation of \ensuremath{\sim}50 narrow resonances (some 20 MHz full width at half maximum). These resonances are due to autodetachment from a diffuse negative-ion complex consisting of an electron weakly bound (\ensuremath{\sim}5 ${\mathrm{cm}}^{\ensuremath{-}1}$) by the dipolar electric field of the neutral. Electric fields of 70 V/cm are adequate to detach the electron from the lower (bound) levels where autodetachment is not possible. Such states should exist for all neutrals with dipole moments greater than about 2 D.

Ab initio MRD-CI calculation of the electron affinities of Si and SiH: study of three stable states of the respective negative ions

Large DZP AO basis multi-reference through singles and doubles CI (MRD-CI) calculations are reported for the lowest electronic states of the negative ions of the silicon atom and its hydride SiH and also for the corresponding neutral species. The energy differences between electronic states within a given ionic system are found to agree with known experimental data to within about 0.05 eV at the estimated full CI level of treatment. The corresponding electron affinity results are in similarly good agreement with experiment (maximal errors of 0.07-0.14 eV), so that the combination of a high quality AO basis including semi-diffuse p and d as well as f-type polarisation functions plus a large-scale multi-reference CI including full CI correction is demonstrated to provide a high degree of reliability for the computation of such quantities. Spectroscopic parameters for SiH- (including De values) and Franck-Condon factors for a series of electron detachment processes involving the lowest states of this ion and other neutral SiH species are also presented.

Investigation of negative ion states in HCl and HF by configuration interaction methods

Multi-reference configuration interaction calculations are employed for the study of Born-Oppenheimer potential energy curves in HF/HF- and HCl/HCl-. Large gaussian basis sets including negative ion functions as well as diffuse s, p and d AOs are employed thereby. In HCl- a repulsive 2Σ+ state emerges from the calculations approximately 4·2 eV above the HCl X 1Σ+ ground state; no such entity could be observed in HF- in the energy range treated. All other CI roots which produce potential curves parallel to and above the X 1Σ+ curve are found to possess quite diffuse charge distributions in the basis set variations undertaken and can therefore not be considered resonant states but rather as discrete representations of free-electron species in the HX + e- continuum. For large internuclear distances the HF- and HCl- curves lie below those of the neutral species, whereby the crossing between the X 2Σ+ ionic and X 1Σ+ curves are calculated to occur at 3·2 a 0 in HCl/HCl- and 2·6 a 0 in HF/HF-. Finally it is arg...

Shape resonances, overtones, and electron energy loss spectroscopy of gas phase and physisorbed diatomic molecules

Electron energy loss spectra of O2 and N2 physisorbed on metallic substrates showing a series of high overtone losses have recently been reported. In the case of N2, the intense overtone excitation is credited to the formation of a well-known temporary negative ion state with a resonance lifetime ∼10−15 s for gas phase N2−. The principal distinction between the gaseous and physisorbed molecule EELS spectrum is a significant depletion of the overtone intensity which has been attributed to a surface-induced decrease in the resonance lifetime. In the present work, a time dependent quantum mechanical model applicable to vibrational excitation in resonance scattering is outlined which quantitatively accounts for the observed spectra and, in particular, the surface modifications to the gas phase results. The essential feature of the model is one in which the intramolecular dynamics of the intermediate state is characterized by nuclear propagation over a harmonic potential curve spatially displaced from the ground state curve for a time duration equal to the resonance lifetime. The resulting calculated overtone spectra agree well with the experimentally observed ones. The results suggest that the physisorbed N−2 lifetime is about 40% of that of the free molecule.

Low-lying electronic states of CSi-and electron affinity of CSi according to ab initio MRD-CI calculations

Large scale MRD-CI calculations including highly excited configurations have been carried out in several large AO basis sets to determine the electronic structure of the CSi- ion. Only two bound states are found (2 Sigma + and 2 Pi ), in contrast to the results for isovalent C2-, in which a third such species (2 Sigma u+) is also known. Results for the separated atomic species C, C-, Si and Si- employing the same theoretical method indicate that the energy separations between such negative ion states can be obtained to an accuracy of 0.1-0.2 eV. The present calculated electron affinity for CSi of 1.98 eV is thought to be of this accuracy, and it is therefore suggested that a previous estimate for this quantity of 4 eV based on indirect experimental evidence must be reconsidered.

Electron attachment to the perfluoroalkanes n-CNF2N+2 (N=1–6) and i-C4F1 a)

Parent and fragment negative ion formation from seven perfluoroalkanes [n-CNF2N+2 (N=1–6) and i-C4F10] under low-energy (0–10 eV) electron impact has been studied using a time-of-flight mass spectrometer. For CF4, C2E6, and C3F8 only fragment anions were observed, F− being the most abundant. For n-C4F10 a weak parent ion was observed, but again the predominant ion was F−. For i-C4F10, n-C5F12, and n-C6F14 the parent negative ions were the most abundant with relative cross sections peaking at 0.6 eV and autodetachment lifetimes from 10 to 100 μs depending on the molecular size and electron energy. In addition to the parent negative ion and the F− ion, fragment negative ions of the form CNF−2N+1, CNF−2N, CNF−2N−1 (with N=1–6) have been detected. The relative cross sections for all observed negative ions have been measured and corrected for the finite width of the electron pulse using an unfolding procedure. The positions of the dissociating negative ion states (NISs) shift to lower energies with increasing size of the molecule. Possible fragmentation mechanisms of the NISs leading to the production of the observed fragment negative ions have been suggested and discussed. From the appearance onsets of a number of fragment negative ions, various C–C and C–F bond dissociation energies, heats of formation, and electron affinities EA of certain fragments have been determined and are reported. It was found that the EA of perfluorocarbon radicals increases with increasing size of these radicals, and similar behavior is indicated also for the perfluoroalkane molecules themselves. The separation times of the dissociating fragments and the autodetachment lifetimes of the extremely short-lived (∼10−15 s) and dissociating NISs of CF4 and C2F6 were estimated. The intensity of the parent anion as a function of molecular size and geometry is discussed, and the relative intensities of the fragment negative ions are rationalized on the basis of the present work and relevant data from electron swarm studies.

Hartree-Fock calculations on negative ion states of chromium hexacarbonyl

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHartree-Fock calculations on negative ion states of chromium hexacarbonylL. G. Vanquickenborne and J. VerhulstCite this: J. Am. Chem. Soc. 1983, 105, 7, 1769–1772Publication Date (Print):April 1, 1983Publication History Published online1 May 2002Published inissue 1 April 1983https://doi.org/10.1021/ja00345a012RIGHTS & PERMISSIONSArticle Views61Altmetric-Citations12LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (506 KB) Get e-Alerts Get e-Alerts

Formation of gas-phase negative ions in vinylene carbonate

The formation and structure of negative ions from vinylene carbonate (C 3O 3H 2) have been studied in gas-phase collision experiments, using both low-energy electrons (<10 eV) and potassium atoms (<40 eV) as projectiles. The two major dissociative attachment resonances, producing C 2H 2O − and C 2H 2O 2 −, exhibit large cross-sections and peak at energies close to the calculated energies of the 2 A 2 and 2 B 1 π-negative-ion states of vinylene carbonate. The ion C 2H 2O − is metastable with respect to autodetachment, and its lifetime decreases rapidly with increasing electron energy over the width of the dissociation resonance. Collisions of potassium atoms with vinylene carbonate indicate that formation of C 2H 2O 2 − is the more exothermic reaction. The ion CO 3 − is detected only in potassium collisions. A simple analysis involving molecular orbital theory together with a consideration of the resonance structures of the compound negative-ion state is presented which accounts for the major decay modes of the compound states of vinylene carbonate.

ChemInform Abstract: ELECTRON ATTACHMENT TO HALOCARBONS OF ENVIRONMENTAL INTEREST: CHLOROETHANES

Electron attachment to the chlorofluoroethanes 1,1‐C2Cl2F4, 1,2‐C2Cl2F4, 1,1,1‐C2Cl3F3, and 1,1,2‐C2Cl3F3 was investigated in dilute mixtures with nitrogen and argon using the electron swarm method. The 1,1,1‐C2Cl3F3 molecule has a very large electron attachment rate constant at thermal energy (2.8×10−7 cm3 s−1); the rate constant for this molecule decreases monotonically with increasing electron energy above thermal. The other chlorofluoroethanes investigated attach electrons less strongly and show maxima in the rate constant vs mean electron energy at ∼0.5 eV. For all four compounds, the measured rate constants are due primarily to dissociative electron attachment producing Cl−. Electron attachment cross sections were determined for these halocarbons which showed the existence of several negative ion states below ∼2 eV. Additionally, the temperature dependence of electron attachment to 1,1‐C2Cl2H4 was investigated from 323–473 K. The measured rate constants and unfolded cross sections indicated electron attachment to a repulsive negative ion state from the v=0 and v=1 levels of the neutral molecule.

Electron-transmission study of the temporary anion states of substituted pyridines

Electron-transmission spectroscopy has been employed in a study of the temporary negative-ion states of 2-, 3- and 4-methylpyridine, 2-, 3- and 4-chloropyridine, 2-, 3- and 4-aminopyridine, 2-, 3- and 4-acetylpyridine and 2- and 4-vinylpyridine. The effect of substitution on the normally unoccupied orbitals, as well as that of replacement of a CH group by a nitrogen atom, is found to be related to the coefficient of the molecular orbital at the site of substitution. The latter effect, however, is much less pronounced for the unfilled than for the filled orbitals. We attribute this to changes in geometry of the aza derivatives and to the greater diffuseness of the anion wavefunction compared with that of the cation. A simple Hückel MO treatment, the equivalent of the LCBO method for filled orbitals, is applied to the unfilled orbitals of the vinylpyridines and acetylpyridines, and yields the energies of these short-lived anion states quite satisfactorily.

Electron attachment to halocarbons of environmental interest: Chloroethanes

Electron attachment to the chlorofluoroethanes 1,1-C2Cl2F4, 1,2-C2Cl2F4, 1,1,1-C2Cl3F3, and 1,1,2-C2Cl3F3 was investigated in dilute mixtures with nitrogen and argon using the electron swarm method. The 1,1,1-C2Cl3F3 molecule has a very large electron attachment rate constant at thermal energy (2.8×10−7 cm3 s−1); the rate constant for this molecule decreases monotonically with increasing electron energy above thermal. The other chlorofluoroethanes investigated attach electrons less strongly and show maxima in the rate constant vs mean electron energy at ∼0.5 eV. For all four compounds, the measured rate constants are due primarily to dissociative electron attachment producing Cl−. Electron attachment cross sections were determined for these halocarbons which showed the existence of several negative ion states below ∼2 eV. Additionally, the temperature dependence of electron attachment to 1,1-C2Cl2H4 was investigated from 323–473 K. The measured rate constants and unfolded cross sections indicated electron attachment to a repulsive negative ion state from the v=0 and v=1 levels of the neutral molecule.

Broadband photon yield of Kr excited by monoenergetic electron impact. Part II: 12–15 eV

The broadband photon yield in the spectral range 165–650 nm of Kr excited by monoenergetic electrons with energies from 12 to 15 eV has been measured. Several negative-ion states are observed both below and above the 2P3/2 ionization threshold. No structures are detected above the 2P1/2 limit, even with a total accumulation of 200 million counts per observation point.

Forward Electron Scattering in Benzene; Forbidden Transitions and Excitation Functions

AbstractA systematic study of vibronic excitation in benzene via forward electron scattering was carried out using a novel type of a trochoidal electron spectrometer. Energy‐loss spectra in the energy range 1.0–9.5 eV, with residual energies 0.03–20 eV as well as excitation functions for individual vibrational levels of some of the triplet and singlet states are presented and discussed. Following observations were made. (1) A new s‐type Rydberg series with quantum defect δ = 0.86. (2) Additional information on the complex 6–6.5 eV band. (3) A new core excited shape resonance at 6.5 eV. (4) A narrow Feshbach resonance at 5.87 eV, The new spectrometer is suggested as a tool for routine study of forbidden transitions and negative ion states in organic molecules.