O. V. Smirnov

Interaction of 3He2+ and Ar6+ ions with acetylene, ethylene, and ethane molecules

Time-of-flight mass spectroscopy methods are employed for studying processes occurring during capture of electrons by 3He2+ and Ar6+ multiply charged ions with energy 6z keV (z is the ion charge) from C2Hn molecules (n = 2, 4, 6) with different multiplicities of C-C bonds. Fragmentation schemes of the molecular ions formed in such processes are established from analysis of correlations of recording times for all fragment ions. The absolute values of the cross sections of capture of an electron and capture with ionization are measured, as well as the cross sections of formation of fragment ions in these processes. The absolute values of total capture cross sections for several electrons are determined.

Fragmentation of polyatomic ions produced by electron-loss collisions of butane and isobutane molecules with ions of kiloelectronvolt energy

Fragmentation accompanying the loss of electrons by butane and isobutane (C4H10) molecules in collisions with energy H+, He2+, and Ar6+ ions of kiloelectronvolt energies is studied. The electron density functional technique is applied to CnH2n+2 alkane molecules and their respective CnH2n+2+ ions to carry out quantum-chemical calculations of the atomic spacing, electron total energy for the initial configuration of the ionizing molecules and ions in the ground state, and atomic bond breaking energy necessary to produce different ion fragments. The fragmentation energy is correlated with the fragmentation probability. It is shown that the relative cross sections of ion fragmentation depend primarily on the related energy consumption. However, the process cross section is also strongly affected by the initial configuration of C4H10 isomer molecules, as well as by the amount of dangling and arising atomic bonds involved in the formation of each ion fragment.

Electron Capture and Fragmentation at Ar6+–C60 Collisions

Abstract Mass/charge spectra of recoil ionic fragments formed in collisions of C60 molecules with keV‐energy Ar6+ projectile ions were studied using registration of the fragments in coincidence with the projectile captured certain number of electrons s at the same single collision. Different channels of the fragmentation accompanied by additional ionization were observed. The degree of fragmentation is caused mainly by electronic excitation transferred predominantly to C60 at the electron capture and increases with s value from 1 to 6.

Fragmentation of D- and L-enantiomers of amino acids through interaction with 3He2+ ions

The relative cross section of processes attendant on the capture of an electron by 12-keV 3He2+ ions are measured by time-of-flight mass spectrometry for leucine (C6H13NO2), methionine (C5H11NO2S), and glutmic acid (C5H9NO4) molecules. No differences between the formation relative cross sections of different fragment ions for the D- and L-enantiomeric forms of the amino acids are revealed. The spectrum of glutamic acid fragments taken at temperatures above 110°C is explained by decomposition of the acid with the formation of pyroglutamic acid (C5H7NO3) and water. The results are compared with published data on fragmentation of the same molecules via electron-impact ionization.

Capture of an Electron by Ions in Methionine and Norleucine Molecules

The relative cross sections of processes taking place when H+ and He2+ ions with an energy of 6z keV (z is the ionic charge) capture an electron from molecules of C5H11NO2S methionine (proteogenic amino acid) and C6H13NO2 norleucine (nonproteogenic amino acid) are measured by time-of-flight mass spectrometry (a methionine molecule transforms into a norleucine molecule by substituting the CH2 group for the S heteroatom). The fragmentation pattern of resulting molecular ions is established from correlation analysis of the detection times of all fragment ions. The results are compared with experimental data for fragmentation of the same molecules ionized by electrons and photons. In these amino acids, the pattern of molecular ion fragmentation is found to depend on the type of molecule ionization. However, the detachment cross section of the COOH neutral group or residue (neutral or charged) R of a side chain of the amino acid is invariably among the largest. The relative cross sections of capture with single and double ionization of molecules are measured.

Elementary processes during collisions of ions with tryptophan molecules

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.

Ionization of glycine molecules by α-particles with keV energies

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 Ep = 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.

Dissociation of alkane ionized molecules

The subject of investigation is the fragmentation of variously charged molecular ions arising in col-lisions of several kiloelectronvolt H+, He2+, and Ar6+ ions with molecules of the simplest alkanes (from methane to butane). Using the method of time-of-flight mass spectrometry, the formation cross sections of dissociation-induced fragment ions are measured. The dissociation takes place when an incident ion captures an electron from a methane, ethane, or propane molecule. The role of additional ionization of the molecule, which accompanies the electron capture by the incident ion, is elucidated. The kinetic energy spectrum for protons resulting from the fragmentation of multiply charged alkane ions is determined. The most plausible kinetic energies of protons depending on the degree of ionization and molecule size fall into the range 1–25 eV. It is shown that, when the molecule loses several electrons, the kinetic energies of protons are governed by Coulomb interaction between all fragment ions and are determined by their flying apart from the relative spatial arrangement of corresponding atoms in a parent molecule.

Formation of Carbonic Cluster Ions at the Ionization of Fullerenes and Multiatomic Molecules of Hydrocarbons

Formation probability of carbonic ionized clusters arising from the collisions between multiply charged ions and fullerene – C60, toluene – C7H8, benzene – C6H6 and butane – C4H10 molecules has been measured. He2+ and Ar6+ projectile ions have been used for the ionization and following fragmentation of polyatomic molecules. The charge state analysis of projectile ions after collisions made it possible to control the minimal number of electrons removed from the target molecule and, as a result, the qualitative control of its excitation energy. The recoil fragment ions formed at target molecule dissociation have been analyzed on mass and charge by time of flight system (TOF).

Fragmentation of Multiply Ionized Fullerene Molecules

The dissociation of C60 fullerene molecules has been studied by means of an analysis of the kinetic energies of charged fragments formed upon the capture of several electrons from C60 by multiply charged Ar6+ ions. The kinetic energies of fragment ions of a multiply ionized C60 molecule are distributed in accordance with the Coulomb explosion mechanism of dissociation.