Electron Impact Ionization of Metastable States of Diatomic Molecules

The Binary-Encounter Bethe approach was applied to the estimation of total ionization induced by electron impact in metastable states of diatomic molecules. The cross sections recently obtained for N2 and CO are reviewed and the new results for H2 are presented, discussing their reliability through the comparison with other theoretical methods.

Electron spectra for twisted electron collisions

Ionization collisions have important consequences in many physical phenomena, and the mechanism that leads to ionization is not universal. Double differential cross sections (DDCSs) are often used to identify ionization mechanisms because they exhibit features that distinguish close collisions from grazing collisions. In the angular DDCS, a sharp peak indicates ionization through a close binary collision, while a broad angular distribution points to a grazing collision. In the DDCS energy spectrum, electrons ejected through a binary encounter collision result in peak at an energy predicted from momentum conservation. These insights into ionization processes are well-established for plane wave projectiles. However, the recent development of sculpted particle wave packets reopens the question of how ionization occurs for these new particle wave forms. We present theoretical DDCSs for (e,2e) ionization of atomic hydrogen for electron vortex projectiles. Our results predict that the ionization mechanism for vortex projectiles is similar to that of non-vortex projectiles, but that the projectile’s momentum uncertainty causes noticeable changes to the shape and magnitude of the vortex DDCSs. Specifically, there is a broadening and splitting of the angular DDCS peak for vortex projectiles, and an increase in the cross section for high energy ejected electrons.

Binary-Encounter Model for Direct Ionization of Molecules by Positron-Impact

We introduce two models for the computation of direct ionization cross sections by positron impact over a wide range of collision energies. The models are based on the binary-encounter-Bethe model and take into account an extension of the Wannier theory. The cross sections computed with these models show good agreement with experimental data. The extensions improve the agreement between theory and experiment for collision energies between the first ionization threshold and the peak of the cross section. The models are based on a small set of parameters, which can be computed with standard quantum chemistry program packages.

A Binary-Encounter-Bethe approach to compute electron-impact partial ionization cross sections of plasma relevant molecules like Hexamethyldisiloxane and Silane

The electron-impact partial ionization cross sections (PICS) of the fragments are reported from threshold to 5~keV energy using the modified form of the binary-encounter-Bethe model. The scaling using mass spectrometry data ensures that the cross sections are of correct order of magnitude. The total ionization cross sections (TICS) were obtained by summing the PICS of fragments. The PICS and TICS obtained from the modified-binary-encounter-Bethe model are in excellent agreement with the experimental results and theoretical results. The molecules investigated are hexamethyldisiloxane (HMDSO) and silane. Both these species are highly relevant in plasma processing where the PICS are required over an extended energy range. The study of ionization process in conjunction with mass spectrometry provides correct estimates of the contribution that each charged ion makes to the TICS. The present approach can be easily extended to any species provided ion energetics, and relative cation abundances data are available.

Іонізація електронами молекул глютамінової кислоти та глютаміну

Проведено комплекснi (експериментальнi i теоретичнi) дослiдження виходу позитив-них iонiв молекул глютамiнової кислоти (Glu-Acid) i глютамiну (Gln) в газовiй фазi, утворених в результатi дисоцiативної iонiзацiї цих амiнокислот електронним ударом. Експеримент проводився на установцi з монопольним мас-спектрометром ти-пу MX-7304A в дiапазонi масових чисел 10–150 Da. Дослiджено мас-спектри молекул глютамiнової кислоти i глютамiну при рiзних температурах, динамiку виходу iонiв-фрагментiв в iнтервалi температур випаровування вихiдної речовини 310–430 К та детально проаналiзовано особливостi процесiв утворення iонiв-фрагментiв таких молекул електронним ударом. Проведено ab initio розрахунки потенцiалiв iонiзацiї глютамiнової кислоти i глютамiну в адiабатичному наближеннi та за енергiями зв’язку HOMO- i LUMO-орбiталей нейтральних молекул. Отримано сумарнi перерiзи одноелектронної iонiзацiї обох молекул електронним ударом в Binary-Encounter-Bethe моделi та за формулою Гризiнського. Показано, що розрахованi молекулярнi константи добре узгоджуються з отриманими експериментальними даними.