Publications (419)1007.46 Total impact
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ABSTRACT: We measured differential cross sections for elastic (rotationally integrated) electron scattering on pyrimidine, both as a function of angle up to 180(∘) at electron energies of 1, 5, 10, and 20 eV and as a function of electron energy in the range 0.114 eV. The experimental results are compared to the results of the fixednuclei Schwinger variational and Rmatrix theoretical methods, which reproduce satisfactorily the magnitudes and shapes of the experimental cross sections. The emphasis of the present work is on recording detailed excitation functions revealing resonances in the excitation process. Resonant structures are observed at 0.2, 0.7, and 4.35 eV and calculations for different symmetries confirm their assignment as the X̃(2)A2, Ã(2)B1, and B̃(2)B1 shape resonances. As a consequence of superposition of coherent resonant amplitudes with background scattering the B̃(2)B1 shape resonance appears as a peak, a dip, or a step function in the cross sections recorded as a function of energy at different scattering angles and this effect is satisfactorily reproduced by theory. The dip and peak contributions at different scattering angles partially compensate, making the resonance nearly invisible in the integral cross section. Vibrationally integrated cross sections were also measured at 1, 5, 10 and 20 eV and the question of whether the fixednuclei cross sections should be compared to vibrationally elastic or vibrationally integrated cross section is discussed.  [Show abstract] [Hide abstract]
ABSTRACT: We report theoretical as well as (normalized) experimental differential and integral cross sections for vibrationally elastic scattering of lowenergy electrons from chloroethane, C2H5Cl, also known as ethyl chloride. The theoretical cross sections were computed using the Schwinger multichannel variational method in the singlechannel approximation, with polarization effects included via virtual excitations. Cross section measurements were made at incident energies ranging from 1 to 30 eV and at scattering angles from &${10}^{\circ }$; to &${125}^{\circ }$;. We compare our data to previous results for C2H5Cl and for the related molecule chloromethane.  [Show abstract] [Hide abstract]
ABSTRACT: We report theoretical as well as (normalized) experimental differential and integral cross sections for vibrationally elastic scattering of lowenergy electrons from chloromethane, CH3Cl, also known as methyl chloride. The theoretical cross sections were computed using the Schwinger multichannel variational method in the singlechannel approximation, with polarization effects included via virtual excitations. Cross section measurements were made at incident energies ranging from 0.5 to 100 eV and at scattering angles from to 5° to 125°. We compare our data to earlier previous results for this molecule.  [Show abstract] [Hide abstract]
ABSTRACT: We report differential and integral cross sections for electronic excitation of methanol by lowenergy electron impact. Cross sections were measured for the four lowestlying excited states at incident electron energies from 9 to 20 eV and at scattering angles from 5° through 130°. The measured cross sections were normalized against previously reported elastic scattering data determined using the relative flow method. Corresponding crosssection calculations were carried out using the complex Kohn variational method within a 7channel closecoupling scheme and using the Schwinger multichannel method within an 11channel closecoupling scheme.  [Show abstract] [Hide abstract]
ABSTRACT: We describe a theoretical approach to molecular photoionization that includes firstorder corrections to the dipole approximation. The theoretical formalism is presented and applied to photoionization of H2 over the 20 to 180eV photon energy range. The angleintegrated cross section σ, the electric dipole anisotropy parameter βe, the molecular alignment anisotropy parameter βm, and the firstorder nondipole asymmetry parameters γ and δ were calculated within the singlechannel, staticexchange approximation. The calculated parameters are compared with previous measurements of σ and βm and the present measurements of βe and γ+3δ. The dipole and nondipole angular distribution parameters were determined simultaneously using an efficient, multiangle measurement technique. Good overall agreement is observed between the magnitudes and spectral variations of the calculated and measured parameters. The nondipole asymmetries of He 1s and Ne 2p photoelectrons were also measured in the course of this work.  [Show abstract] [Hide abstract]
ABSTRACT: We report a combined experimental and theoretical investigation of dissociative electron attachment (DEA) to the nucleobase uracil. Using ion momentum imaging experiments employing a DEA reaction microscope we have measured 3dimensional momentum distributions of specific anionic fragments following DEA to uracil by 6 eV electrons. From the measured anion fragment kinetic energy we determine the possible dissociation pathways and the total kinetic energy release. We employ electronic structure and electron scattering calculations to determine the probability for electron attachment in the molecular frame. Combining these calculations with the imaging measurements, we reveal several key features of the coupled electronic and nuclear dynamics of DEA.  [Show abstract] [Hide abstract]
ABSTRACT: Normalized experimental differential and integral cross sections for vibrationally elastic scattering of lowenergy electrons from isobutanol (C4H9OH) are presented. The differential cross sections are measured at incident energies from 1 to 100 eV and scattering angles from 5 degrees to 130 degrees. These cross sections are compared to earlier experimental and theoretical results for isobutanol and nbutanol, as well as to results for smaller alcohols and for alkanes. Further comparisons are made with calculated cross sections for isobutylamine (C4H9NH2) and for smaller amines, including ethylamine (C2H5NH2), dimethylamine (CH3NHCH3), the two C3H7NH2 isomers npropylamine and isopropylamine, and ethylene diamine (NH2C2H4NH2). The calculated cross sections are obtained using the Schwinger multichannel method. The comparisons illuminate the role of molecular structure in determining the angular distribution of resonantly scattered electrons.  [Show abstract] [Hide abstract]
ABSTRACT: We report results of the application of a fully ab initio approach for simulating timeresolved molecularframe photoelectron angular distributions around conical intersections in CS_2. The technique employs wave packet densities obtained with the multiple spawning method in conjunction with geometry and energydependent photoionization matrix elements. The robust agreement of these results with measured molecularframe photoelectron angular distributions for CS_2 demonstrates that this technique can successfully elucidate, and disentangle, the underlying nuclear and photoionization dynamics around conical intersections in polyatomic molecules.  [Show abstract] [Hide abstract]
ABSTRACT: We report differential and integral cross sections for excitation of the 3B1, 1B1, 3A2, 1A2, 3A1 and 1A1 states of H2O by 9–20 eV electrons. The measurements are taken by conventional differential electron energy loss spectroscopy techniques, while the calculations employ the Schwinger multichannel method within a tenchannel approximation. The new data are compared with previous experimental and theoretical results. The present measurements and calculations agree reasonably well both with each other and with prior theoretical efforts but show discrepancies with prior measurements. Reasons for those discrepancies are considered and discussed. 
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ABSTRACT: We report results from a combined experimental and computational study of lowenergy electron interactions with acetaldehyde in the gas phase. Differential cross sections for elastic electron scattering were measured at selected incident energies from 1 to 50 eV, while corresponding firstprinciples calculations were carried out up to 30 eV. Integral and momentumtransfer cross sections were derived from the angledifferential data. The role of resonances in the scattering is examined and comparison is made to previous results for acetaldehyde and for its analogs, formamide and formic acid.  [Show abstract] [Hide abstract]
ABSTRACT: In order to understand and optimize processes occurring during the ignition of plasma and its consequences in postdischarge for an internal combustion engine, especially considering the spark plug, we have produced in this work some basic information necessary to modeling spark ignition in alcohol fuelled engines. Total cross sections of electron scattering by methanol and ethanol molecules in the energy range from 60 to 500 eV are reported, using the linear transmission method based on the BeerLambert law to first approximation. Aditionally to that, measurements and calculations of differential cross sections for elastic lowenergy (rotationally unresolved) electron scattering were also discussed, for impact energies of 1, 2, 5, 10, 15, 20, 30, 50, and 100 eV and for scattering angles of 5°130°. The measurements were obtained using the relative flow method with an aperture source, and calculations using two different implementations of the Schwinger multichannel method, one that takes all electrons into account and is adapted for parallel computers, and another that uses pseudopotentials and considers only the valence electrons.  [Show abstract] [Hide abstract]
ABSTRACT: We present absolute experimental cross sections for elastic scattering, vibrational excitation by electron impact and for dissociative electron attachment to 1,3butadiyne, as well as calculations of the elastic cross sections.  [Show abstract] [Hide abstract]
ABSTRACT: New experimental and theoretical data are presented for excitation of the 3B1 and 1B1 states of water by lowenergy (915 eV) electron impact.  [Show abstract] [Hide abstract]
ABSTRACT: We report measured and calculated differential crosssections for inelastic scattering of lowenergy electrons by water leading to excitation of the dissociative (1b_1 → 4ɑ_1) ^(1,3)B_1 states. The measurements were taken using conventional energyloss spectroscopy at incident energies of 9, 10, 12, 15, and 20 eV for scattering angles from 10◦ to 130◦. The calculations were carried out using the Schwinger multichannel method, with a Borndipole correction applied in the singlet excitation channel. Integral excitation cross sections for the ᾶ^3B_1 and Ã^1B_1 states are also derived from the differential cross section results.  [Show abstract] [Hide abstract]
ABSTRACT: We report results from a combined experimental and computational study of lowenergy electron interactions with acetaldehyde in the gas phase. Differential cross sections for elastic electron scattering were measured at selected incident energies from 1 to 50 eV, while corresponding firstprinciples calculations were carried out up to 30 eV. Integral and momentumtransfer cross sections were derived from the angledifferential data. The role of resonances in the scattering is examined and comparison is made to previous results for acetaldehyde and for its analogs, formamide and formic acid.  [Show abstract] [Hide abstract]
ABSTRACT: We report experimental and theoretical (Schwinger MultiChannel method with polarization effects) differential crosssections (DCS) for low energy elastic electron scattering from tetrahydrofuran. The data are for incident energies from 0.75 to 30eV and the experimental scattering angles range from 10^o to 130^o. Agreement between theory and experiment is very good across the range of this data. Comparisons with previous experiments is also very good in general. We will also report DCSs for vibrational excitation of this target for energies up to 15eV and similar scattering angles.  [Show abstract] [Hide abstract]
ABSTRACT: Pyrazine (C4H4N2) is a model molecule for studying electron interactions with nucleases. Also pyrazine is an ideal target, due to its high symmetry (D2h), for theoreticians to investigate electron collisions with complex DNA/RNA bases. In this work we present absolute elastic differential cross sections and elastic excitation functions for scattering of lowenergy electrons by pyrazine measured using a crossed electrontarget beam apparatus at the Australian National University. A comparison is also made between pyrazine cross sections with previously measured pyrimidine and benzene cross sections. Since all those molecules are similar in structure and considered as analogues to nucleobases, we intend to discuss similarities and differences in electron scattering results between three molecules. 
Article: Excitation of the \tilde{a}\,^3B_1 and \tilde{A}\,^1B_1 states of H2O by lowenergy electron impact
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ABSTRACT: We report measured and calculated differential crosssections for inelastic scattering of lowenergy electrons by water leading to excitation of the dissociative (1b1 → 4a1) 1, 3B1 states. The measurements were taken using conventional energyloss spectroscopy at incident energies of 9, 10, 12, 15, and 20 eV for scattering angles from 10° to 130°. The calculations were carried out using the Schwinger multichannel method, with a Borndipole correction applied in the singlet excitation channel. Integral excitation cross sections for the \tilde{a}\,^3B_1 and \tilde{A}\,^1B_1 states are also derived from the differential cross section results.  [Show abstract] [Hide abstract]
ABSTRACT: We explore the application of a quantum vibrational wavepacket dynamics formulation of femtosecond energy and angleresolved photoelectron spectroscopy to the study of nuclear and electron dynamics. The formulation incorporates geometry and energydependent photoionization matrix elements and is well suited for studies of nonadiabatic dynamics where nuclear and electronic degrees of freedom are coupled. In this paper we explore two aspects of angleresolved pump–probe photoelectron spectroscopy, using NO2 and NaI as examples. The first is a refinement of femtosecond photoelectron spectroscopy in which the time derivative of the velocity map image is seen to more readily characterize the nuclear wavepacket dynamics in nonadiabatic regions. The other is an analysis to extract the effects of electronicstate fluctuation from subfemtosecond scale photoelectron dynamics. Within the framework of the Born–Huang (Oppenheimer) expansion where the total wavefunction is expressed in products of stationarystate electronic wavefunctions and timedependent nuclear wavepackets, we seek to identify how the effect of electron dynamics might be manifested in principle.
Publication Stats
9k  Citations  
1,007.46  Total Impact Points  
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Institutions

19672015

California Institute of Technology
 • Arthur Amos Noyes Laboratory of Chemical Physics
 • Division of Chemistry and Chemical Engineering
 • Gates and Crellin Laboratories of Chemistry
Pasadena, California, United States


2014

National Research Council Canada
Ottawa, Ontario, Canada


20102013

California State University, Fullerton
 Department of Physics
Fullerton, California, United States


2005

Universidade Federal do Paraná
 Department of Physics
Curityba, Paraná, Brazil


2000

University of Minnesota Duluth
 Department of Chemistry and Biochemistry
Duluth, Minnesota, United States


19941995

Louisiana State University
 Department of Chemistry
Baton Rouge, Louisiana, United States


1987

NASA
Вашингтон, West Virginia, United States


1981

Bielefeld University
Bielefeld, North RhineWestphalia, Germany 
Pasadena City College
Pasadena, Texas, United States
