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

Experimental and Theoretical Cross Sections for Molecular-frame Electron-impact Excitation-ionization of D₂

We present both experimental and theoretical results for the dissociative ionization of D2 molecules induced by electron impact. Cross sections are determined in the molecular frame and are fully differential in the energies and emission angles of the dissociation fragments. Transitions are considered from the X1Σg+ electronic ground state of D2 to the 2sσg, 2pπu and 2pσu excited states of D2+. The experimental results are compared to calculations performed within the molecular four-body distorted-wave framework to describe the multicenter nature of the scattering process. The cross sections reveal a dramatic dependence on both the alignment of the internuclear axis with respect to the direction of the projectile momentum and on the symmetry of the excited dissociating state which is energetically resolved

Dynamical (e, 2e) Studies Using Tetrahydrofuran As a DNA Analog

Triple differential cross sections for the electron-impact ionization of the outer valence orbital of tetrahydrofuran have been measured using the (e, 2e) technique. The measurements have been performed with coplanar asymmetric kinematics, at an incident electron energy of 250 eV and at an ejected electron energy of 10 eV, over a range of momentum transfers. The experimental results are compared with theoretical calculations carried out using the molecular three-body distorted wave model. The results obtained are important for gaining an understanding of electron driven processes at a molecular level and for modeling energy deposition in living tissue

The following article appeared in S

The binding energies of the p-, m-, and o-difluorobenzene-H 2 O complexes have been measured by velocity map ion imaging to be 922Ϯ 10, 945Ϯ 10, and 891Ϯ 4 cm −1 , respectively. The lack of variation provides circumstantial evidence for water binding to the three isomers via the same interaction, viz. an in-plane O-H¯F hydrogen bond to one of the fluorine atoms on the ring, with a second, weaker interaction of the water O atom with an ortho hydrogen, as determined previously for the p-difluorobenzene-H 2 O complex ͓Kang et al., J. Phys. Chem. A 109, 767 ͑2005͔͒. The ground state binding energies for the difluorobenzene-H 2 O complexes are ϳ5 % -11% larger than that for benzene-H 2 O, where binding occurs to the electrons out-of-plane. However, in the S 1 state the binding energies of the o-and p-difluorobenzene-H 2 O complexes are smaller than the benzene-H 2 O value, raising an interesting question about whether the geometry at the global energy minimum remains in-plane in the excited electronic states of these two complexes. Recoil energy distributions for dissociation of p-difluorobenzene-H 2 O have been measured from the 3 1 , 5 2 , and 3 1 5 1 levels of the excited electronic state. These levels are 490, 880, and 1304 cm −1 , respectively, above the dissociation threshold. Within the experimental uncertainty, the recoil energy distributions are the same for dissociation from these three states, with average recoil energies of ϳ100 cm −1 . These recoil energies are 60% larger than was observed for the dissociation of p-difluorobenzene-Ar, which is a substantially smaller increase than the 400% seen in a comparable study of dissociation within the triplet state for pyrazine-Ar, -H 2 O complexes. The majority of the available energy is partitioned into vibration and rotation of the fragments

Ionization and Ionization-Excitation of Helium to the n=1-4 States of He⁺ by Electron Impact

We present experimental and theoretical results for the electron-impact-induced ionization of ground-state helium atoms. Using a high-sensitivity toroidal electron spectrometer, we measured cross-section ratios for transitions leading to the first three excited states of the residual helium ion relative to the transition leaving the ion in the ground state. Measurements were performed for both symmetric- and asymmetric-energy-sharing kinematics. By presenting results as a ratio, a direct comparison can be made between theoretical and experimental predictions without recourse to normalization. The experimental data are compared to theoretical predictions employing various first-order models and a second-order hybrid distorted-wave + convergent R matrix with pseudostates (close-coupling) approach. All the first-order models fail in predicting even the approximate size of the cross-section ratios. The second-order calculations are found to describe the experimental data for asymmetric-energy-sharing with reasonable fidelity, although significant disparities are evident for the symmetric-energy-sharing cases. These comparisons demonstrate the need for further theoretical developments, in which all four charged particles are treated on an equal footing

A Dynamical (e,2e) Investigation of the Structurally Related Cyclic Ethers Tetrahydrofuran, Tetrahydropyran, and 1,4-Dioxane

Triple differential cross section measurements for the electron-impact ionization of the highest occupied molecular orbitals of tetrahydropyran and 1,4-dioxane are presented. For each molecule, experimental measurements were performed using the (e,2e) technique in asymmetric coplanar kinematics with an incident electron energy of 250 eV and an ejected electron energy of 20 eV. With the scattered electrons being detected at -5°, the angular distributions of the ejected electrons in the binary and recoil regions were observed. These measurements are compared with calculations performed within the molecular 3-body distorted wave model. Here, reasonable agreement was observed between the theoretical model and the experimental measurements. These measurements are compared with results from a recent study on tetrahydrofuran [D. B. Jones, J. D. Builth-Williams, S. M. Bellm, L. Chiari, C. G. Ning, H. Chaluvadi, B. Lohmann, O. Ingolfsson, D. Madison, and M. J. Brunger, Chem. Phys. Lett. 572, 32 (2013)] in order to evaluate the influence of structure on the dynamics of the ionization process across this series of cyclic ethers

Dynamical (e,2e) Investigations of Structurally Related Cyclic Ethers

Experimental and theoretical cross sections are presented for electron-impact ionization of a series of cyclic ethers

The partitioning of energy amongst vibration, rotation, and translation during the dissociation of p-difluorobenzene-Ar neutral and cation complexes

Susan M. Bellm and Warren D. Lawranc

Dynamical (e,2e) Investigations of Tetrahydrofuran and Tetrahydrofurfuryl Alcohol As DNA Analogues

Triple differential cross section measurements for the electron-impact ionization of the highest occupied molecular orbital of tetrahydrofuran (THF) are reported. Experimental measurements were performed using the (e,2e) technique in asymmetric coplanar kinematics with an incident electron energy of 250 eV and an ejected electron energy of 20 eV. With the scattered electrons being detected at -5⁰, the angular distribution of the ejected electrons was observed. These measurements are compared with calculations performed within the molecular 3-body distorted wave (M3DW) model, and against previous measurements on THF and tetrahydrofurfuryl alcohol to further understand the role that kinematics and structure play in electron-impact ionization