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T D Märk - One of the best experts on this subject based on the ideXlab platform.
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Electron Attachment to formamide clusters in helium nanodroplets.
The journal of physical chemistry. A, 2010Co-Authors: F. Ferreira Da Silva, T D Märk, Stephan Denifl, Nikos L. Doltsinis, Andrew M. Ellis, P ScheierAbstract:Electron Attachment to formamide clusters in helium nanodroplets is reported for the first time. In contrast to the gas phase, parent anions are seen following low energy Electron Attachment to both the monomer and the small clusters. This is attributed to formation of dipole (or quadrupole) bound anions. In addition to the bare anions, the mass spectra also show the monomer and clusters with attached helium atoms. The affinity for attaching helium atoms strongly varies with cluster size; for example, the dimer anion is more than 10 times more likely to bind one or more helium atoms than the monomer. Possible binding sites for the helium atoms are discussed.
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Investigations Of Electron Attachment To Nitro‐Compounds Towards Explosives
AIP Conference Proceedings, 2009Co-Authors: A. Mauracher, M. Probst, T D Märk, Stephan Denifl, P ScheierAbstract:Electron Attachment to gas phase nitrobenzene, all three isomers of mononitrotoluene and 2,4,6‐trinitrotoluene is studied by means of two crossed Electron‐molecular beam experiments. We point out the formation of long‐lived metastable parent anions and the most abundant anions produced via dissociative Electron Attachment (DEA). The experimental results are supported by quantum‐chemical calculations, to determine the Electronic configuration of selected molecular orbitals or the electrostatic potential mapped on an isosurface of the total Electron density to find preferential sites of Electron Attachment.
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dissociative Electron Attachment to gas phase alanine
Chemical Physics Letters, 2005Co-Authors: S Ptasinska, P Scheier, Stephan Denifl, Pietro Candori, S Matejcik, T D MärkAbstract:Abstract Using a high resolution Electron energy monochromator the dissociative Electron Attachment (DEA) to the gas phase l -alanine is studied by means of the mass spectrometric detection of the product anions. Alanine and the previously studied amino acid glycine exhibit several common features due to the possibility of Electron Attachment to the unoccupied π* orbital of the –COOH group. The largest DEA cross-section of about 1.5 × 10 −20 m 2 is observed for the production of the (A − H) − ion at the Electron energy of 1.27 eV. This ion is the major reaction product at Electron energies below 5 eV. At higher incident Electron energies several smaller fragment anions are formed via core excited resonances at about 5.5 and 9.0 eV.
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Dissociative Electron Attachment to gas-phase glycine.
Analytical and bioanalytical chemistry, 2003Co-Authors: S Ptasinska, S Denifl, A Abedi, P Scheier, T D MärkAbstract:By using a high-resolution Electron energy monochromator low-energy Electron Attachment to gas-phase glycine (H2NCH2COOH, or G) has been studied by means of mass spectrometric detection of the product anions. In the same way as for several other biologically relevant molecules no stable parent anion was formed by free Electron Attachment. The largest dissociative Electron Attachment (DEA) cross-section, approximately 5x10(-20) m2, was observed for (G-H)-+H at an Electron energy of 1.25 eV. Glycine and formic acid (HCOOH) have several common features, because a precursor ion can be characterized by Electron Attachment to the unoccupied pi* orbital of the -COOH group. At higher incident Electron energies several smaller fragment anions are formed. Except for H-, which could not be observed in this study, there was good agreement with an earlier investigation by Gohlke et al.
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Low energy Electron Attachment to CH3CN
Chemical Physics Letters, 2003Co-Authors: W. Sailer, P Scheier, Andrzej Pelc, Nigel J. Mason, Paulo Limão-vieira, Jumras Limtrakul, M. Probst, T D MärkAbstract:Low energy Electron Attachment cross sections for acetonitrile (CH3CN) are reported in the energy range from about 0 up to 10 eV determined with an energy resolution of 140 meV. Electron Attachment is shown to be a purely dissociative process with the production of the five anionic fragments: CH2CN−, CHCN−, CCN−, CN− and CH3− observed in two energy regions, the first between 1 and 4 eV, the second in excess of 6 eV. Quantum chemical and trajectory calculations have been carried out to complement the experimental results.
So Hirata - One of the best experts on this subject based on the ideXlab platform.
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Higher-order equation-of-motion coupled-cluster methods for Electron Attachment
Journal of Chemical Physics, 2007Co-Authors: Muneaki Kamiya, So HirataAbstract:High-order equation-of-motion coupled-cluster methods for Electron Attachment (EA-EOM-CC) have been implemented with the aid of the symbolic algebra program TCE into parallel computer programs. Two types of size-extensive truncation have been applied to the Electron-Attachment and cluster excitation operators: (1) the Electron-Attachment operator truncated after the 2p-1h, 3p-2h, or 4p-3h level in combination with the cluster excitation operator after doubles, triples, or quadruples, respectively, defining EA-EOM-CCSD, EA-EOM-CCSDT, or EA-EOM-CCSDTQ; (2) the combination of up to the 3p-2h Electron-Attachment operator and up to the double cluster excitation operator [EA-EOM-CCSD(3p-2h)] or up to 4p-3h and triples [EA-EOM-CCSDT(4p-3h)]. These methods, capable of handling Electron Attachment to open-shell molecules, have been applied to the Electron affinities of NH and C2, the excitation energies of CH, and the spectroscopic constants of all these molecules with the errors due to basis sets of finite sizes ...
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higher order equation of motion coupled cluster methods for Electron Attachment
Journal of Chemical Physics, 2007Co-Authors: Muneaki Kamiya, So HirataAbstract:High-order equation-of-motion coupled-cluster methods for Electron Attachment (EA-EOM-CC) have been implemented with the aid of the symbolic algebra program TCE into parallel computer programs. Two types of size-extensive truncation have been applied to the Electron-Attachment and cluster excitation operators: (1) the Electron-Attachment operator truncated after the 2p-1h, 3p-2h, or 4p-3h level in combination with the cluster excitation operator after doubles, triples, or quadruples, respectively, defining EA-EOM-CCSD, EA-EOM-CCSDT, or EA-EOM-CCSDTQ; (2) the combination of up to the 3p-2h Electron-Attachment operator and up to the double cluster excitation operator [EA-EOM-CCSD(3p-2h)] or up to 4p-3h and triples [EA-EOM-CCSDT(4p-3h)]. These methods, capable of handling Electron Attachment to open-shell molecules, have been applied to the Electron affinities of NH and C2, the excitation energies of CH, and the spectroscopic constants of all these molecules with the errors due to basis sets of finite sizes removed by extrapolation. The differences in the Electron affinities or excitation energies between EA-EOM-CCSD and experiment are frequently in excess of 2 eV for these molecules, which have severe multideterminant wave functions. Including higher-order operators, the EA-EOM-CC methods predict these quantities accurate to within 0.01 eV of experimental values. In particular, the 3p-2h Electron-Attachment and triple cluster excitation operators are significant for achieving this accuracy.
Lal A. Pinnaduwage - One of the best experts on this subject based on the ideXlab platform.
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TEMPERATURE DEPENDENCE OF Electron Attachment TO METHYLENE CHLORIDE
Journal of Chemical Physics, 1999Co-Authors: Lal A. Pinnaduwage, D. L. Mccorkle, Weixing DingAbstract:Temperature dependence of dissociative Electron Attachment to methylene chloride in the Electron energy range of 0–10 eV was studied in a high-temperature Electron swarm apparatus. The measurements were made using N2 and Ar as buffer gases. From the measured Electron Attachment rate constants, the Electron Attachment cross sections at 300, 400, and 500 K were determined using an unfolding technique. The maximum Electron Attachment cross sections at 300, 400, and 500 K were ≈3.1×10−18, ≈8.2×10−18, and ≈1.7×10−17 cm2, and occurred at Electron energies of ≈0.8, ≈0.65, and ≈0.55 eV, respectively. The increase in Electron Attachment to methylene chloride with temperature is attributed to the increase in the vibrational energy of the molecule.
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Electron Attachment to boron trichloride
Journal of Applied Physics, 1998Co-Authors: Cumali Tav, Panos G. Datskos, Lal A. PinnaduwageAbstract:Low-energy Electron Attachment to BCl3 was measured using an Electron swarm technique. The parent negative ion, BCl3−, was observed within a narrow Electron range close to thermal energy. Previous negative ion measurements in BCl3 discharges, which yielded seemingly inconsistent results, can be shown to be self-consistent based on the present observations.
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Electron Attachment to thermally excited trichlorotrifluoroethane (1, 1, 2-)
Journal of Physics D: Applied Physics, 1997Co-Authors: Panos G. Datskos, Cumali Tav, Isidor Sauers, Lal A. PinnaduwageAbstract:Electron Attachment to trichlorotrifluoroethane (1, 1, 2-) was investigated in buffer gases of and Ar using a high-temperature Electron swarm apparatus. The negative ion intensity was also measured as a function of Electron energy using an Electron beam apparatus. The Electron Attachment rate constant, , was measured in the mean Electron energy range, , 0.043 to 4.7 eV and over a temperature, T, range 300 to 700 K in the Electron swarm experiments. The Electron Attachment rate constant was found to first increase slightly with increasing temperature and subsequently decrease for K. Our room-temperature Electron beam study showed that 1, 1, 2- attaches Electrons predominantly via dissociative negative ion states and revealed that the Electron Attachment cross section exhibits three main peaks: one at eV producing , a second one at eV due to and a third one at eV also producing . The Electron Attachment cross sections obtained using an Electron swarm-unfolding technique show that the peak at eV observed in the Electron beam study is actually composed of three peaks; one at eV and two more at higher Electron energies but below 1.5 eV.
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NOVEL TECHNIQUE FOR REAL-TIME MONITORING OF Electron Attachment TO LASER-EXCITED MOLECULES
The Journal of Chemical Physics, 1996Co-Authors: Lal A. Pinnaduwage, Panos G. DatskosAbstract:We report a new experimental technique that is capable of monitoring Electron Attachment to laser‐excited molecules in real time; the time resolution is limited only by the time constant of the detection circuit and was ∼100 ps for the experiments reported here. This technique provides information on the lifetime of the excited states responsible for Electron Attachment, and also allows determination of Electron Attachment cross sections involved. Results on dissociative Electron Attachment to ArF‐excimer‐laser‐irradiated NO are reported: Electron Attachment occurred to the A 2Σ+(ν=3) state populated via the absorption of a single photon, and to highly excited states populated via two‐photon absorption; the cross section for low‐energy Electron Attachment to the A 2Σ+(ν=3) state was ∼3 orders of magnitude larger compared to that for the A 2Σ+(ν=0). Decay of the Electrons over the ∼200 ns lifetime of the A 2Σ+(ν=3) state was directly monitored. Negative‐ion formation that occurred via the A 2Σ+(ν=3) state ...
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Electron Attachment to Excited Molecules
Linking the Gaseous and Condensed Phases of Matter, 1994Co-Authors: L. G. Christophorou, Lal A. Pinnaduwage, Panos G. DatskosAbstract:Studies on Electron Attachment to molecules rotationally/vibrationally excited thermally or via infrared-laser excitation showed that the effect of internal energy of a molecule on its Electron Attachment properties depends on the mode-dissociative or nondissociative-of Electron Attachment. They quantified the effect of the internal energy of the molecule on the rate of destruction (by autodissociation or by autodetachment) of its parent transient anion. Generally, increases in ro-vibrational molecular energy increase the cross section for dissociative Electron Attachment and decrease the effective cross section for parent anion formation due mainly to increased autodetachment. These findings and their understanding are discussed. A discussion is given, also, of recent investigations of Electron Attachment to Electronically excited molecules, especially photoenhanced dissociative Electron Attachment to long- and short-lived excited Electronic states of molecules produced directly or indirectly by laser irradiation. These studies showed that the cross sections for dissociative Electron Attachment to Electronically excited molecules usually are many orders of magnitude larger than those for the ground-state molecules. The new techniques that have been developed for such studies are briefly described also.
P Scheier - One of the best experts on this subject based on the ideXlab platform.
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Electron Attachment to formamide clusters in helium nanodroplets.
The journal of physical chemistry. A, 2010Co-Authors: F. Ferreira Da Silva, T D Märk, Stephan Denifl, Nikos L. Doltsinis, Andrew M. Ellis, P ScheierAbstract:Electron Attachment to formamide clusters in helium nanodroplets is reported for the first time. In contrast to the gas phase, parent anions are seen following low energy Electron Attachment to both the monomer and the small clusters. This is attributed to formation of dipole (or quadrupole) bound anions. In addition to the bare anions, the mass spectra also show the monomer and clusters with attached helium atoms. The affinity for attaching helium atoms strongly varies with cluster size; for example, the dimer anion is more than 10 times more likely to bind one or more helium atoms than the monomer. Possible binding sites for the helium atoms are discussed.
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Investigations Of Electron Attachment To Nitro‐Compounds Towards Explosives
AIP Conference Proceedings, 2009Co-Authors: A. Mauracher, M. Probst, T D Märk, Stephan Denifl, P ScheierAbstract:Electron Attachment to gas phase nitrobenzene, all three isomers of mononitrotoluene and 2,4,6‐trinitrotoluene is studied by means of two crossed Electron‐molecular beam experiments. We point out the formation of long‐lived metastable parent anions and the most abundant anions produced via dissociative Electron Attachment (DEA). The experimental results are supported by quantum‐chemical calculations, to determine the Electronic configuration of selected molecular orbitals or the electrostatic potential mapped on an isosurface of the total Electron density to find preferential sites of Electron Attachment.
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dissociative Electron Attachment to gas phase alanine
Chemical Physics Letters, 2005Co-Authors: S Ptasinska, P Scheier, Stephan Denifl, Pietro Candori, S Matejcik, T D MärkAbstract:Abstract Using a high resolution Electron energy monochromator the dissociative Electron Attachment (DEA) to the gas phase l -alanine is studied by means of the mass spectrometric detection of the product anions. Alanine and the previously studied amino acid glycine exhibit several common features due to the possibility of Electron Attachment to the unoccupied π* orbital of the –COOH group. The largest DEA cross-section of about 1.5 × 10 −20 m 2 is observed for the production of the (A − H) − ion at the Electron energy of 1.27 eV. This ion is the major reaction product at Electron energies below 5 eV. At higher incident Electron energies several smaller fragment anions are formed via core excited resonances at about 5.5 and 9.0 eV.
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Dissociative Electron Attachment to gas-phase glycine.
Analytical and bioanalytical chemistry, 2003Co-Authors: S Ptasinska, S Denifl, A Abedi, P Scheier, T D MärkAbstract:By using a high-resolution Electron energy monochromator low-energy Electron Attachment to gas-phase glycine (H2NCH2COOH, or G) has been studied by means of mass spectrometric detection of the product anions. In the same way as for several other biologically relevant molecules no stable parent anion was formed by free Electron Attachment. The largest dissociative Electron Attachment (DEA) cross-section, approximately 5x10(-20) m2, was observed for (G-H)-+H at an Electron energy of 1.25 eV. Glycine and formic acid (HCOOH) have several common features, because a precursor ion can be characterized by Electron Attachment to the unoccupied pi* orbital of the -COOH group. At higher incident Electron energies several smaller fragment anions are formed. Except for H-, which could not be observed in this study, there was good agreement with an earlier investigation by Gohlke et al.
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Low energy Electron Attachment to CH3CN
Chemical Physics Letters, 2003Co-Authors: W. Sailer, P Scheier, Andrzej Pelc, Nigel J. Mason, Paulo Limão-vieira, Jumras Limtrakul, M. Probst, T D MärkAbstract:Low energy Electron Attachment cross sections for acetonitrile (CH3CN) are reported in the energy range from about 0 up to 10 eV determined with an energy resolution of 140 meV. Electron Attachment is shown to be a purely dissociative process with the production of the five anionic fragments: CH2CN−, CHCN−, CCN−, CN− and CH3− observed in two energy regions, the first between 1 and 4 eV, the second in excess of 6 eV. Quantum chemical and trajectory calculations have been carried out to complement the experimental results.
A. A. Viggiano - One of the best experts on this subject based on the ideXlab platform.
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Electron Attachment to fluorocarbon radicals
The Journal of chemical physics, 2012Co-Authors: Nicholas S. Shuman, Thomas M. Miller, A. A. ViggianoAbstract:Thermal Electron Attachment rate constants for a series of small fluorocarbon radicals (CF2, C2F3, 1-C3F7, 2-C3F7, C3F5, CF3O) were measured from 300 to 600 K using the variable Electron and neutral density Attachment mass spectrometry method. With the exception of CF2, for which no Attachment was observed, all species exclusively underwent dissociative Attachment to yield F−. The magnitude and temperature dependences of the rate constants varied significantly between species; however, Attachment was in all cases inefficient, never exceeding 2% of the calculated collisional value. The data are interpreted and extrapolated to conditions inaccessible to the experiment using a kinetic modeling approach to the Electron Attachment process.
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Electron Attachment to Fluorocarbon Radicals and Unstable Molecules: CF2 and C2F5
Journal of Physics: Conference Series, 2012Co-Authors: Thomas A. Field, Karola Graupner, Thomas M. Miller, Nicholas S. Shuman, Jeffrey F. Friedman, Sean A. Haughey, Chris A. Mayhew, A. A. ViggianoAbstract:Electron Attachment to unstable fluorocarbon molecules has been investigated; CF2 - no dissociative Electron Attachment was observed, C2F5 – Electron Attachment observed at close to zero Electron energy with the observation of C2F5−.
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Dissociative Electron Attachment to C2F5 radicals
The Journal of chemical physics, 2012Co-Authors: Sean A. Haughey, Thomas A. Field, Thomas M. Miller, Nicholas S. Shuman, Jeffrey F. Friedman, Judith Langer, A. A. ViggianoAbstract:Dissociative Electron Attachment to the reactive C2F5 molecular radical has been investigated with two complimentary experimental methods; a single collision beam experiment and a new flowing afterglow Langmuir probe technique. The beam results show that F− is formed close to zero Electron energy in dissociative Electron Attachment to C2F5. The afterglow measurements also show that F− is formed in collisions between Electrons and C2F5 molecules with rate constants of 3.7 × 10−9 cm3 s−1 to 4.7 × 10−9 cm3 s−1 at temperatures of 300–600 K. The rate constant increases slowly with increasing temperature, but the rise observed is smaller than the experimental uncertainty of 35%.
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Electron Attachment to propargyl chloride, 305-540 K.
The Journal of chemical physics, 2010Co-Authors: Joseph C. Bopp, Thomas M. Miller, Nicholas S. Shuman, Jeffrey F. Friedman, A. A. ViggianoAbstract:Electron Attachment to propargyl chloride (HC≡C–CH2Cl) was studied in a flowing-afterglow Langmuir-probe apparatus from 305 to 540 K. The sole ion product in this temperature range is Cl−. Electron Attachment is very inefficient, requiring correction for a competing process of Electron recombination with molecular cations produced in reaction between Ar+ and propargyl chloride and subsequent ion-molecule reactions. The Electron Attachment rate coefficient was measured to be 1.6×10−10 cm3 s−1 at 305 K and increased to 1.1×10−9 cm3 s−1 at 540 K.
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Electron Attachment to Ni(PF3)4 and Pt(PF3)4
The Journal of chemical physics, 2008Co-Authors: Jeffrey F. Friedman, Thomas M. Miller, A. A. Viggiano, Jessica K. Friedman-schaffer, G. K. Rekha, Amy E. StevensAbstract:An experimental study has been made of thermal Electron Attachment to the transition-metal trifluorophosphine complexes Ni(PF3)4 and Pt(PF3)4 using a flowing-afterglow Langmuir-probe apparatus. Both complexes are efficient at Electron Attachment, although the rate constants are somewhat less than collisional. The rate constant for Electron Attachment to Ni(PF3)4 is 1.9×10−7cm3s−1 at room temperature, about a factor of 2 less than collisional. The activation energy is 39±5meV for the Attachment reaction. The rate constant for Electron Attachment to Pt(PF3)4 is 5.4×10−8cm3s−1 at room temperature, and the activation energy is 84±8meV. For both complexes, a PF3 ligand is lost on Electron Attachment, and only the M(PF3)3− ion is observed in the negative-ion mass spectrum. Density functional calculations were carried out on Ni(PF3)4 and various fragments in order to describe the thermochemistry of the Attachment reaction.