Enhanced electron attachment to vibrationally and electronically excited molecules

Author

Cumali Tav

Date of Award

12-2000

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Physics

Major Professor

Lal. A. Pinnaduwage

Committee Members

Panos G. Datskos, D. L. McCorkle

Abstract

Electron attachment studies on vibrationally and electronically excited states have been measured using two different techniques: Electron swarm and electron electron-swarm type techniques. In electron swarm technique, the attachment of electrons produced in a plane by alpha-particle ionization of carrier gas (N₂ and Ar gases) to vibrationally excited states of the ground electronic state populated via temperature increase has been conducted in the mean electron energy range, (ε), 0.04 to 4.8 eV, over the temperature range, T, 300 to 700 K and over the total gas number density, N_t, 2.25 to 15.5 x 10¹⁹ molecules/cm³ These studies have been presented in Part I including technologically important molecules: Methylene Chloride (C₂H₂CI₂), Boron Trichloride (BCI₃), and Trichlorotrifluoroethane (1,1,2- C₂CI₃F₃). Electron attachment rate constants, k_α((ε),T), have been measured as a function of mean electron energy in Ar and N₂ gases at different temperatures. Using swarm unfolding technique, electron attachment cross sections, δ_&alpha,(ε,T), have been obtained as a function of electron energy by unfolding k_&alpha((ε),T) at each temperature. The results of these measurements have showed that the dissociative electron attachment cross sections have increased with the increase of vibrational energies. In the electron-swarm type technique, electrons produced via photoionization and attaching molecules produced via photoexcitation have been produced indirectly concomitantly in over the laser-irradiated region via single excimer-laser pulse. The excitation of molecules that were excited to energies above the ionization potential (IP) caused the population of core-excited Rydberg states (HR). The electrons produced via photoionization were attached to the concomitantly produced highly-excited molecules leading to negative ion formation under the high-pressure environment provided by Ar or N₂ gases. In these experiments two different methods have been used: two-electrode arrangement and three-electrode arrangement. The two-electrode arrangement technique has provided information on the lifetimes of the excited molecules as well as estimates of various experimental parameters including the electron attachment rate constant of excited molecules. The other technique, the three-electrode arrangement, has provided information about the density of charged species including electrons and negative ions, and the estimation of electron attachment rate constant as well as the other parameters such as number of photons needed to form a negative ion and so on. These results have been presented in Part II including the other technologically important molecules: Benzene (C₆H₆), Oxygen (O₂), and Dichlorodifluoromethane (CCI₂F₂). It has been shown that the electron attachment to highly-excited molecules was extremely efficient process leading to enormous electron attachment cross sections, δ_α ~ 10^-10 cm², which were many orders of magnitude larger compared to those cross sections measured in ground electronic state.

Recommended Citation

Tav, Cumali, "Enhanced electron attachment to vibrationally and electronically excited molecules. " PhD diss., University of Tennessee, 2000.
https://trace.tennessee.edu/utk_graddiss/8427