Off-campus UNL users: To download campus access dissertations, please use the following link to log into our proxy server with your NU ID and password. When you are done browsing please remember to return to this page and log out.

Non-UNL users: Please talk to your librarian about requesting this dissertation through interlibrary loan.

Absolute differential scattering cross-sections of electrons from neon, nitrogen and methyl chloride

Xueying Shi, University of Nebraska - Lincoln

Abstract

The relative flow technique is used to obtain absolute DCS in a crossed-beam experiment. A novel gas handling system was designed to facilitate these measurements. The absolute DCS of electrons scattered from neon have been measured from 7 eV down to 0.25 eV. At energies of 2 eV and lower, our results are in excellent agreement with MERT and recent ab initio calculation. At energies higher than 2 eV, our results are in excellent agreement with those of Williams. Thus we propose that neon can be used as a benchmark to test the overall performance of the electron spectrometer at low energies. The angular dependence of absolute vibrationally-elastic DCS of electrons scattered from N$\sb2$ have been measured at 0.55 eV, 1.50 eV, and $\sim$2.22 eV, the second elastic peak of the $\sp2\Pi\sb{\rm g}$ resonance. Our results at these two lower energies are much larger than the previous experimental results, but in close agreement with theoretical calculations by Morrison. By extrapolating our curves to 0$\sp\circ$ and 180$\sp\circ$ using Morrison's curves as a guide, integration gave the total vibrationally-elastic cross sections at these two energies. Our results are within 2-4% of the experimentally measured total cross sections. Methyl Chloride is the simplest saturated hydrocarbon with a single chlorine atom substitution. Two resonances have been assigned in CH$\sb3$Cl, the $a\sb1$(C-Cl,$\sigma\sp*)$ resonance at 3.45 eV and the e(C-H,$\sigma\sp*$) resonance at 5.5 eV. In the elastic channel, the measurements show that dipole scattering dominates at low energies and in the forward direction. In inelastic channels, the C-Cl stretch mode $\nu\sb3(a\sb1)$ is strongly excited by the $\sigma\sp*$(C-Cl) shape resonance, and the C-H stretch mode $\nu\sb4(e)$ is the strongest one excited by the e resonance. The angular dependences for excitation of these two modes are relatively flat. The shapes cannot be explained solely by a few leading terms in the angular momentum expansion arising from the resonance. This suggests that non-resonant scattering may contribute to the angular distribution of these two modes.

Subject Area

Atoms & subatomic particles|Molecules

Recommended Citation

Shi, Xueying, "Absolute differential scattering cross-sections of electrons from neon, nitrogen and methyl chloride" (1992). ETD collection for University of Nebraska-Lincoln. AAI9308195.
https://digitalcommons.unl.edu/dissertations/AAI9308195

Share

COinS