The fragmentation processes of adenine (Ade, C5H5N5) and cyclodiglycine (DKP, C4H6N2O2) ions formed in capturing a single electron during the interaction of molecules in the gas phase with C2+ and O2+ ions with an energy of 12 keV are studied by time-of-flight mass spectrometry. The experimentally observed dependence of the relative fragmentation cross section of molecular ions on the type of projectile is qualitatively explained within the framework of the quasi-molecular model. Using the multiconfiguration method of a self-consistent field in a complete active space (CASSCF), the fragmentation reaction paths of Ade+ and DKP+ ions are calculated. The calculated energy values of the appearance of fragments are in close agreement with the available experimental data.

The mechanism of radiation damage to 2,5-diketopiperazine (DKP, C4H6N2O2) molecules in the gas phase upon interaction with He2+ ions with an energy Ep = 4 keV/u has been investigated. The relative cross sections of various elementary processes occurring in single collisions of DKP with ions have been measured for the first time. The channels of fragmentation processes of singly charged ions have been studied experimentally. The DFT method was used to calculate the geometry of molecules and singly charged DKP ions, as well as the energies of the main experimentally observed channels of fragmentation of these ions.

Исследован механизм процессов фрагментации ионов аденина (Ade, C 5 H 5 N 5 ), происходящих при взаимодействии молекул, находящихся в газовой фазе, с ионами энергий порядка кэВ. Измерены относительные сечения различных элементарных процессов, осуществляющихся при однократных столкновениях ионов с молекулами. Экспериментально изучены каналы процессов фрагментации однозарядных ионов Ade + . Методом самосогласованного поля в полном активном пространстве ( CASSCF) выполнен расчет геометрии молекул и однозарядных ионов Ade + , а также путей реакций основных экспериментально наблюдаемых каналов фрагментации этих ионов.

The mechanism of the fragmentation processes of adenine ions (Ade, C 5 H 5 N 5 ) occurring during the interaction of molecules in the gas phase with ions energies of the order of keV is studied. The relative cross sections of various elementary processes occurring in single collisions of ions with molecules are measured. The channels of the fragmentation processes of singly charged Ade + ions are experimentally studied. The complete active space self-consistent field (CASSCF) method is used to calculate the geometry of the molecules and singly charged Ade + ions, as well as the reaction paths of the main experimentally observed fragmentation channels of these ions.

The mechanism of radiation damage to 2,5-diketopiperazine (DKP, C4H6N2O2) molecules in the gas phase upon interaction with He2+ ions with an energy Ep = 4 keV/u has been investigated. The relative cross sections of various elementary processes occurring in single collisions of DKP with ions have been measured for the first time. The channels of fragmentation processes of singly charged ions have been studied experimentally. The DFT method was used to calculate the geometry of molecules and singly charged DKP ions, as well as the energies of the main experimentally observed channels of fragmentation of these ions.

The single electron capture process from adenine molecules by H+, 3He+, N+, O+, and Ne+ ions with an energy of 6.3 keV has been studied. It was found that when one electron is captured by He+ and Ne+ ions, the dissociative capture process is dominant, which is fundamentally different from the processes of capture by singly charged ions of atoms with a lower ionization potential and multiply charged ions, as well as from the process of electron impact ionization. This effect is qualitatively explained within the framework of a quasimolecular model.

The single electron capture process from adenine molecules by H+, 3He+, N+, O+, and Ne+ ions with an energy of 6.3 keV has been studied. It was found that when one electron is captured by He+ and Ne+ ions, the dissociative capture process is dominant, which is fundamentally different from the processes of capture by singly charged ions of atoms with a lower ionization potential and multiply charged ions, as well as from the process of electron impact ionization. This effect is qualitatively explained within the framework of a quasimolecular model. Keywords: dissociative capture, nucleic acid bases, fragmentation, Landau-Zener model.

In this paper we have studied a mechanism for radiation damage of gas phase molecules of glycine [Gly] and dipeptide derivatives of glycine, such as diglycine [Gly-Gly], cyclo(glycylglycyl) [cyclo(Gly-Gly)] and glycylleucine [Gly-Leu] by the impact of He2+ ions with energy E-p = 4 keV/u. Relative cross sections of different elementary processes occurring in single collisions between dipeptide derivatives of glycine and ions have been measured for the first time. The fragmentation channels of both singly and multiply charged molecular ions have been studied experimentally. It has been shown that in the process of Gly-Gly sublimation, cyclization in the crystalline sample takes place, which results in formation of cyclo(Gly-Gly). Using the DFT method, the geometry of molecules and singly charged ions of glycine dipeptide derivatives has been calculated, as well as energies of different experimentally observed fragmentation channels of these ions.

Radiation-induced damage of isolated glycyl–leucine (C 8 H 16 N 2 O 3 ) molecules by the impact of He 2+ ions has been studied. Relative cross sections of the main processes of charged state variation in collision parties and relative cross sections of fragmentation for singly and doubly charged molecular ions formed due to single collisions between glycyl–leucine molecules and He 2+ ions have been determined for the first time. Optimized geometry of the molecule and singly charged molecular ion of glycyl–leucine has been calculated by method of density functional theory.

Radiation damage to isolated glycyl-leucine (C8H16N2O3) molecules caused by interaction with He2+ ions was studied. For the first time, the relative cross sections of the main processes of changes in the charge state of the collision partners and the relative cross sections of the fragmentation processes of singly and doubly charged molecular ions formed during single collisions of glycyl-leucine molecules with ions have been obtained. The optimized geometry of the molecule and singly charged glycyl-leucine ion was calculated using the density functional theory (DFT).

The method of collision spectroscopy, which is based on precision measurement of the kinetic energy of projectile ions after the electron capture process, is used to measure the partial cross sections of the formation of He + ( n ) ions in specific electronic states upon the capture of an electron by 3 He 2+ ions with energy E = 1.4–10 keV/a.m.u. from hydrogen atoms. A target of atomic hydrogen with a dissociation degree of 78% was created at the temperature of a tungsten dissociation cell of 2180 K.

Using collision spectroscopy based on precision measurements of the kinetic energy of projectile ions that capture an electron, we measured the state selective electron capture cross sections of formation of He^+(n) ions at collision 3^He^{2 +} ions with an energy of E = 1.4-10 keV/a.m.u. with hydrogen atoms. The atomic hydrogen target with a degree of dissociation 78% at a temperature of tungsten dissociation cell 2180K has been made.

AbstractThe absolute cross sections of single-electron capture and single-electron capture with dissociation in the interaction between incident He^2+, C^2+, N^2+, and O^2+ ions with energies from 6.4 to 36.4 keV and СО molecules were measured. It is demonstrated that the cross section of dissociative capture is much larger than the cross section of single-electron capture for O^2+ projectile ions. A qualitative explanation for this effect is provided.

Fragmentation of isolated molecular ions of dipeptides produced by alpha-particles was studied by an experimental technique based on time-of-flight analysis of the charge and mass composition of the fragment ions. The study has shown that the N-Glycylglycine sublimation results in the molecule decomposition into cyclo(GlycylGlycyl) and H2O molecule. We have examined a mass-spectrum of the fragments arising in the cyclo(GlycylGlycyl) interaction with α-particles. By analyzing the temperature dependence of the cyclo(GlycylGlycyl) vapor pressure, we have determined sublimation enthalpy ΔHsubl(453K) = (213 ± 9) kJ/mol.

The absolute cross sections of single-electron capture and single-electron capture with dissociation in the interaction between incident He2+, C2+, N2+, and O2+ ions with energies from 6.4 to 36.4 keV and СО molecules were measured. It is demonstrated that the cross section of dissociative capture is much larger than the cross section of single-electron capture for O2+ projectile ions. A qualitative explanation for this effect is provided.

Методом "многостоповой" времяпролетной масс-спектрометрии исследован механизм радиационных повреждений молекул глицина, находящихся в газовой фазе, при взаимодействии с ионами He2+ с энергией Ep = 4 keV/a.m.u. Впервые измерены относительные сечения различных элементарных процессов, происходящих при однократных столкновениях молекул глицина с ионами. Обнаружено различие в фрагментации промежуточных двухзарядных ионов, формирующихся в процессах захвата одного электрона с ионизацией и двухэлектронного захвата, что объясняется разницей в энергии возбуждения молекулярных ионов. DOI: 10.21883/PJTF.2017.07.44470.16531

The method of "multistop" time-of-flight mass spectrometry has been used to study the mechanism of radiation damage to glycine molecules in the gas phase upon their interaction with He2+ ions with energy E (p) = 4 keV/amu. The relative cross sections of various elementary processes occurring in single collisions of glycine molecules with the ions were measured for the first time. A difference was found between the fragmentations of intermediate doubly charged ions formed in capture of a single electron with ionization and in two-electron capture, which is accounted for by the difference between the excitation energies of molecular ions.

Computer simulation is carried out for selecting a compact electron-optical system of the channel for detecting secondary electrons formed during the interaction of xenon atoms or ions with energy of 1-30 keV with Xe atoms. The solid angle of passage of secondary electron beams in a wide range of their initial energies is calculated. The energy spectrum of secondary electrons with various energies is determined by constructing their deceleration curve.

The relative cross sections of elementary processes occurring in single collisions of tryptophan molecules in the gaseous phase with He2+ ions with energy 4 keV/u are measured using time-of-flight mass spectrometry for studying the mechanism of radiation damage of amino acid molecules. The fragmentation channels for intermediate singly and doubly charged tryptophan molecular ions formed during one-electron capture, two-electron capture, and electron capture with ionization are investigated. Significant difference is observed in the mass spectra of fragmentation of intermediate doubly charged ions formed during the capture with ionization and double capture, which is associated with different energies of excitation of {C11H12N2O2}2+* ions.