Brygida Mielewska

Dissociative electron attachment to furan, tetrahydrofuran, and fructose

We study dissociative electron attachment to furan (FN) (C(4)H(4)O), tetrahydrofuran (THF) (C(4)H(8)O), and fructose (FRU) (C(6)H(12)O(6)) using crossed electron/molecular beams experiments with mass spectrometric detection of the anions. We find that FN and THF are weak electron scavengers and subjected to dissociative electron attachment essentially in the energy range above 5.5 eV via core excited resonances. In striking contrast to that, FRU is very sensitive towards low energy electrons generating a variety of fragment ions via a pronounced low energy feature close to 0 eV. These reactions are associated with the degradation of the ring structure and demonstrate that THF cannot be used as surrogate to model deoxyribose in DNA with respect to the attack of electrons at subexcitation energies (<3 eV). The results support the picture that in DNA the sugar moiety itself is an active part in the initial molecular processes leading to single strand breaks.

Ionization and ionic fragmentation of tetrahydrofuran molecules by electron collisions

Electron impact ionization and ionic fragmentation of tetrahydrofuran molecules in the gas phase were studied in the energy range from ionization threshold up to 150 eV using the technique of mass spectrometry. The cation mass spectra, ionization and ionic fragmentation efficiencies were measured over this energy range. Well-resolved mass peaks were detected in the mass range 10-72 amu and assigned to corresponding ionic molecular fragments. The most abundant cation in the mass spectra is at 42 amu. Appearance energies of selected ionic fragments were also determined. Possible ionic fragmentation processes are discussed.

A study of resonance structures in elastic electron scattering from helium, neon, argon, krypton and xenon over the angular range from 100 to 180

Resonance structures corresponding to the 2sS state in He and the np(n + 1) s(S) states in Ne, Ar, Kr and Xe have been studied in elastic electron scattering over the angular range from 100 to 180. A newly developed magnetic angle-changing technique has been used and this has allowed the first observation of these structures at and near to 180. The widths and energies of the resonance states in krypton and xenon have been determined.

Absolute differential cross sections for electron elastic scattering and vibrational excitation in nitrogen in the angular range from 120° to 180°

Absolute differential cross sections for elastic electron scattering and vibrational (v = 0→1) excitation in nitrogen have been measured in the range of scattering angle from 120° to 180° at an incident electron energy of 5 eV. The measurements have been carried out using the magnetic angle-changing technique that allows observation of scattering in the backward direction. These results, together with the existing experimental data for lower scattering angles, give differential cross sections over a wide angular range from close to zero to 180°. The importance of short- and long-range correlation (polarization) interactions for elastic electron scattering at forward and backward directions is discussed.

A study of resonance structures in elastic electron scattering by carbon monoxide and molecular nitrogen in the backward direction

Abstract Resonance structures corresponding to the (3sσ) 2 2 Σ + state in carbon monoxide at 10.044 eV and the (3sσ g ) 2 2 Σ g + state in nitrogen at 11.499 eV have been studied in elastic electron scattering over the range of scattering angle from 95° to 180°. A new magnetic angle-changing technique has been used in the measurements, which has enabled the first observation of these resonance structures at and close to 180°. The width of the 2 Σ + resonance in carbon monoxide has been determined to be 42±3 meV.

Computational studies of a hypocycloidal electron monochromator

A hypocycloidal electron monochromator (HEM) which uses a uniform axial magnetic field and a cylindrical electric field has been investigated in a computational study using the CPO–3D program. Electron trajectories in the monochromator have been calculated and analysed for an incident electron beam which has a finite angular spread. The energy spread of the electron beam at the exit of the monochromator has been studied as a function of the monochromator parameters. It has been found that the energy resolution of the studied HEM is higher than that of an equivalent trochoidal electron monochromator.

Elastic electron scattering in neon in the 110 degree sign -180 degree sign scattering angle range

Differential cross sections for elastic electron scattering in neon have been measured in the angular range of backward scattering from 110 degree sign -180 degree sign at incident energies of 7, 10, and 15 eV. These measurements combined the use of a magnetic angle changer and an electrostatic electron spectrometer. The differential cross sections measured in the above scattering angle range, together with results obtained previously in the range below 110 degree sign , have been integrated to obtain integral elastic and momentum transfer cross sections. Detailed comparison is presented of the measured differential and integral cross sections with the results of various theoretical calculations.