115 research outputs found
Total electron scattering cross sections from thiophene for the (1-300 eV) impact energy range
Experimental electron scattering cross sections for thiophene in the impact energy range from 1 to 300 eV have been measured with a magnetically confined electron transmission-beam apparatus. Random uncertainty limits have been estimated to be less than 5%, and systematic errors derived from acceptance angle limitations have also been identified and evaluated. Experimental values are compared with our previous low energy (1-15 eV) R-matrix and intermediate/high energy (15-300 eV) IAM-SCAR+I calculations finding reasonable agreement, within the combined uncertainty limits. Some of the low energy shape and core-excited resonances predicted by previous calculations are experimentally confirmed in this study
Multiple scattering approach to elastic electron collisions with molecular clusters
We revisit our multiple-scattering method to treat low energy elastic electron collisions with (H2O)2. Calculations are performed for different geometries of the water dimer with different dipole moments. The effect of the dipole moment of the cluster is analysed. The elastic cross sections are compared to R-matrix results. Good agreement is found above 1 eV for all geometries. Results conrm the validity of the technique
Low and intermediate energy electron collisions with the C molecular anion
Calculations are presented which use the molecular R-matrix with
pseudo-states (MRMPS) method to treat electron impact electron detachment and
electronic excitation of the carbon dimer anion. Resonances are found above the
ionisation threshold of C with , and
symmetry. These are shape resonances trapped by the effect of an attractive
polarisation potential competing with a repulsive Coulomb interaction. The
resonances are found to give structure in the detachment cross section
similar to that observed experimentally. Both excitation and detachment cross
sections are found to be dominated by large impact parameter collisions whose
contribution is modelled using the Born approximation.Comment: 18 pages, 5 figures constructed from 8 file
Multiple scattering approach to low-energy electron collisions with the water dimer
Multiple scattering theory is applied to low-energy electron collisions with
a complex target formed of two molecular scatterers. The total T-matrix is
expressed in terms of the T-matrix for each isolated molecule. We apply the
approach to elastic electron-(H2O)2 collisions. Following the method developed
in our previous work on crystalline ice, we impose a cut-off on the dipole
outside the R-matrix sphere and an energy dependent cut-off on the angular
momentum components of the monomer T-matrix. An R-matrix calculation of
electron-dimer collisions is performed in order to evaluate the accuracy of the
multiple scattering approach. The agreement between the two calculations is
very good.Comment: 15 pages, 4 figures New submission: Added references Included PACS
numbers Figure 3 slightly changed Additions made to the Conclusions and
Discussion sectio
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Toward a description of electron-induced dissociative excitation in HO : Investigation of three resonances above the B̃ state
Electron-induced dissociative excitation (DE) is a little studied process of significant applied relevance. Our aim is to provide a theoretical counterpart to earlier experiments [M. J. Jensen, R. C. Bilodeau, O. Heber, H. B. Pedersen, C. P. Safvan, X. Urbain, D. Zajfman, and L. H. Andersen, Phys. Rev. A 60, 2970 (1999)] on DE of HO. For this purpose, we have performed low-energy fixed-nuclei scattering calculations, based on the R-matrix method, for over 1800 geometries of HO. We have identified and characterized three resonances lying above the second (B̃) excited state of HO; their energy, lifetime, and associated quantum defect have been determined. We assess their possible contribution to the DE process
Elastic and inelastic cross sections for low-energy electron collisions with pyrimidine
We present theoretical elastic and electronic excitation cross sections and experimental electronic excitation cross sections for electron collisions with pyrimidine. We use the R-matrix method to determine elastic integral and differential cross sections and integral inelastic cross sections for energies up to 15 eV. The experimental inelastic cross sections have been determined in the 15–50 eV impact energy range. Typically, there is quite reasonable agreement between the theoretical and experimental integral inelastic cross sections. Calculated elastic cross sections agree very well with prior results
A joint theoretical and experimental study for elastic electron scattering from 1,4-dioxane
We present results of measurements and calculations of elastic electron scattering from 1,4-dioxane in the energy range of 0–1000 eV. Absolute differential and integral elastic cross sections have been measured using a crossed electron-molecule beam spectrometer and the relative flow technique, at four energies in the 10–30 eV range and for scattered electrons in the angular range 20°–129°. The measured cross sections are compared with results from R-matrix computations, at the static exchange plus polarization level, calculated at energies between 0–20 eV, and with calculations employing the independent atom model with the screening corrected additivity rule (IAM-SCAR). Those latter computations were conducted at energies between 1 and 1000 eV. Agreement between the measured and R-matrix cross sections was typically found to be good at all common energies, whereas agreement with IAM-SCAR was satisfactory only at 30 eV. To the best of our knowledge, the present results are the first absolute data to be published in the literature for this scattering system
Convergent calculations of positron scattering from molecular hydrogen
An overview is given of the recently developed adiabatic-nuclei convergent closecoupling method for positron-molecule scattering. Fixed-nuclei single-centre calculations of positron-H2 scattering are presented. Particular emphasis is given to demonstrating convergence with increasing size of the basis and the projectile partial-wave expansion. Results are converged to within ±5%
An investigation into electron scattering from pyrazine at intermediate and high energies
Total electron scattering cross sections for pyrazine in the energy range 10-500 eV have been measured with a new magnetically confined electron transmission-beam apparatus. Theoretical differential and integral elastic, as well as integral inelastic, cross sections have been calculated by means of a screening-corrected form of the independent-atom representation (IAM-SCAR) from 10 to 1000 eV incident electron energies. The present experimental and theoretical total cross sections show a good level of agreement, to within 10%, in the overlapping energy range. Consistency of these results with previous calculations (i.e., the R-matrix and Schwinger Multichannel methods) and elastic scattering measurements at lower energies, below 10 eV, is also discussed
Electron scattering from molecules and molecular aggregates of biological relevance
In this Topical Review we survey the current state of the art in the study of low energy electron collisions with biologically relevant molecules and molecular clusters. We briefly describe the methods and techniques used in the investigation of these processes and summarise the results obtained so far for DNA constituents and their model compounds, amino acids, peptides and other biomolecules. The applications of the data obtained is briefly described as well as future required developments
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