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DOE OSTI2017

Electrondriven processes in polyatomic molecules

This project developed and applied scalable computational methods to obtain information about low-energy electron collisions with larger polyatomic molecules. Such collisions are important in modeling radiation damage to living systems, in spark ignition and combustion, and in plasma processing of materials. The focus of the project was to develop efficient methods that could be used to obtain both fundamental scientific insights and data of practical value to applications.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗

DOE OSTI2016

Resonance effects in elastic cross sections for electron scattering on pyrimidine: Experiment and theory

Here, 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 0.1–14 eV. The experimental results are compared to the results of the fixed-nuclei Schwinger variational and R-matrix 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 $\sim\atop{\chi}$ 2 A 2 , $\sim\atop{A}$ 2 B 1 , and $\sim\atop{B}$ 2 B 1 shape resonances. As a consequence of superposition of coherent resonant amplitudes with background scattering the $\sim\atop{B}$ 2 B 1 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 fixed-nuclei cross sections should be compared to vibrationally elastic or vibrationally integrated cross section is discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2011

Low-energy elastic electron interactions with pyrimidine

We present results of measurements and calculations of elastic electron scattering from pyrimidine in the energy range 3-50 eV. Absolute differential and integral elastic cross sections have been measured using a crossed electron-molecule beam spectrometer and the relative flow technique. The measured cross sections are compared with results of calculations using the well-known Schwinger variational technique and an independent-atom model. Agreement between the measured differential cross sections and the results of the Schwinger calculations is good at lower energies but less satisfactory at higher energies where inelastic channels that should be open are kept closed in the calculations.

74 ATOMIC AND MOLECULAR PHYSICS↗