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Temperature Dependence of Electron-Induced Reactions S. Matejcik, M. Stano, I. Ipolyi, E. Vasekova, J. D. Skalny Department of Experimental Physics The electron induced reactions depend on the energy of the electrons and on the initial state of the molecules [1]. The initial state of the molecules can be described by the electronic, vibrational and rotational excitation. In many cases, especially polyatomic molecules, it is very difficult or even impossible to prepare molecule in well defined excited state (vibrational, rotational excitation) in the time window necessary for the experiments with the electrons. Another possibility is to study electron interaction with molecules with well defined temperature (vibrational and rotational excitation). The studies of gas temperature dependencies for electron induced reaction are of practical importance as many media (discharges, plasmas) where these reactions take place are at elevated temperatures. The crossed electron molecule beams apparatus at the department of Plasma physics in Bratislava has been designed for studies of ionization reactions of the electrons with the molecules at elevated temperatures. The temperature dependences of dissociative electron attachment (DEA) reaction to the molecules have been studied in many swarm experiments and it has been shown that the gas temperature in many cases enhance the rate coefficient for this reaction. We have studied the gas temperature dependences of the cross sections for exotherm DEA reactions (e.g. halo-derivatives of methane [2, 3, 4]). Generally, if a reaction of DEA was sensitive to the gas temperature the magnitude of the cross section has been changed only in the low electron energy range (from zero to few hundred meV). The influence of the gas temperature on the electron impact ionization
(Ell) reactions has been studied for molecules CxHy (x=1..3, y=4..8) [5, 6,
7]. We have observed the influence of the temperature (gas temperatures 293
and 690 K) on the values of the ionization energy (IE) of the molecule and
on the values of the appearance energies (AE) of the fragment ions formed
via the reaction of dissociative electron impact ionization. The IE and AE
values were decreasing with the increasing of the gas temperature and the
shifts of the values were proportional to the rotational and vibrational
excitation of the molecules. References |
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