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.

Differential cross sections for scattering of helium atoms formed at collisions of He2+ ions with kinetic energies of 1.97, 3.00, and 7.17 keV/a.m.u with Xe atoms in processes with the formation of slow xenon ions with charges 2-4 have been measured. The projectiles deflection function is calculated. The probability of all these processes occurring at various values of the impact parameter of colliding particles is determined. The role of the electron shells of the Xe atom 5(s,p) and 4(s,p,d) for the capture of two electrons is determined depending on the speed of approach of the colliding particles, the impact parameter and the charge of the formed xenon ions. Keywords: Double electron capture, capture with ionization, scattering differential cross section, impact parameter.

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.

Differential cross sections for scattering of helium atoms formed at collisions of He2+ ions with kinetic energies of 1.97, 3.00, and 7.17 keV/a.m.u with Xe atoms in processes with the formation of slow xenon ions with charges 2 - 4 have been measured. The projectiles deflection function is calculated. The probability of all these processes occurring at various values of the impact parameter of colliding particles is determined. The role of the electron shells of the Xe atom 5 (s, p) and 4 (s, p, d) for the capture of two electrons is determined depending on the speed of approach of the colliding particles, the impact parameter and the charge of the formed xenon ions.

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).

We have measured the cross sections of elementary processes occurring during collisions of impinging 3He2+ particles with kinetic energies in the range 1–100 keV with Xe atoms, which are accompanied with the formation of free electrons and ions in different final charge states: Xen+ (n = 1–6) and He(2 – m)+ (m = 0–2). We distinguish between ionization processes, in which the impinging α particle does not change the charge state, and processes of capture of one or two electrons, which lead to the formation of a singly charged helium ion or atom with additional removal of electrons from the xenon atom to the continuum. We have determined the cross sections of formation of free electrons in each of these processes and calculated the contribution of multielectron processes to the formation of free electrons. It is shown that upon a change in the energy of collisions between 3He2+ ions from 1 to 100 keV (the velocity of an impinging ion changes from 0.12 to 1.2 a.u.), the mechanism of removal of electrons from the xenon atom changes basically. For low approach velocities of particles, the formation of an autoionization state of the quasi-molecule and its subsequent decay take place. At higher velocities (V > 0.7 a.u.), free electrons are mainly formed because of an abrupt change in the potential energy of electrons when a fast α particle approached the nucleus of the xenon atom.

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.

Измерены сечения элементарных процессов при столкновении налетающих ионов 3 Не 2+ с кинетическими энергиями в диапазоне 1-100 keV с атомами Хе, сопровождающиеся образованием свободных электронов и ионов в различных конечных зарядовых состояниях: Хе n+ (n=1-6) и Не (2-m)+ (m=0-2). Выделены процессы ионизации, когда налетающая альфа-частица не меняет зарядового состояния, и процессы захвата одного или двух электронов, ведущие к образованию однозарядного иона или атома гелия с дополнительным удалением электронов из атома ксенона в сплошной спектр. Определены сечения образования свободных электронов в каждом из этих процессов. Определен вклад в образование свободных электронов многоэлектронных процессов. Показано, что при изменении энергии столкновения ионов 3 Не 2+ от 1 до 100 keV (скорости налетающего иона от 0.12 до 1.2 a.u.) принципиально меняется механизм удаления электронов из атома ксенона. При малых скоростях сближения частиц происходит образование автоионизационного состояния квазимолекулы и его последующий распад. При больших скоростях (V>0.7 a.u.) образование свободных электронов в основном обусловлено внезапным изменением потенциальной энергии электронов при сближении быстрой альфа-частицы с ядром атома ксенона. Ключевые слова: захват с ионизацией, многоэлектронные процессы, свободные электроны, квазимолекулярный механизм.

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.

We have measured the absolute values of total cross sections of capture of one and two electrons by He 2+ ions from argon atoms. The differential scattering cross sections have been determined for fast atoms and singly charged helium ions formed in each of these processes (without and with additional ionization of the formed slow argon ion). Measurements have been taken for He 2+ ions with kinetic energy of 6 keV in scattering angle range 0–2.5°. Based on the measured differential cross sections using different model atomic particle interaction potentials, we have calculated the cross sections of these processes as functions of the impact parameter. The probabilities of realization of these processes with electron density distribution in different shells in the target atom have been compared. The applicability of the expressions for the screened Coulomb interaction potentials in the description of scattering of particles that have captured electrons has been demonstrated.

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.

AbstractWe have measured the absolute values of total cross sections of capture of one and two electrons by He^2+ ions from argon atoms. The differential scattering cross sections have been determined for fast atoms and singly charged helium ions formed in each of these processes (without and with additional ionization of the formed slow argon ion). Measurements have been taken for He^2+ ions with kinetic energy of 6 keV in scattering angle range 0–2.5°. Based on the measured differential cross sections using different model atomic particle interaction potentials, we have calculated the cross sections of these processes as functions of the impact parameter. The probabilities of realization of these processes with electron density distribution in different shells in the target atom have been compared. The applicability of the expressions for the screened Coulomb interaction potentials in the description of scattering of particles that have captured electrons has been demonstrated.