Mariusz Zubek

Absolute total electron-scattering cross sections of N2O and OCS in the low-energy region

Abstract Absolute total cross sections for electron scattering from CO, CO 2 and OCS molecules at low energies have been measured. An increase of the cross sections due to the formation of negative ion resonance states was observed.

Measurements of elastic electron scattering in the backward hemisphere

A new experimental method is described which allows the range of scattering angles to be extended to cover the whole of the backward hemisphere, i.e. up to , in measurements of elastic electron scattering. This is achieved by adding a localized magnetic field to the interaction region of a conventional electrostatic electron spectrometer. Measurements are presented of the differential cross section from 30 - for elastic scattering of electrons by argon at an energy of 10 eV, and of the resonance structures due to the states of at the fixed scattering angles of , and .

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.

Formation of CN (B2Σ+) radicals in the vacuum-ultraviolet photodissociation of pyridine and pyrimidine molecules

Formation of the excited CN(B2Σ+) free radicals in the photodissociation of pyridine (C5H5N) and pyrimidine (C4H4N2) molecules was investigated over the energy ranges 16–27 and 14.7–25 eV, respectively. Photon-induced fluorescence spectroscopy was applied to detect the vibrationally and rotationally excited CN radicals by recording the B2Σ+→X2Σ+ emission bands (violet system). The measured dissociation yield curves demonstrate that the CN(B2Σ+) formation occurs via excitation of pyridine and pyrimidine molecules into higher-lying superexcited states. This is followed by rearrangement and isomerization of the excited molecules before dissociation. The vertical excitation energies of the superexcited states were determined and the probable dissociation mechanisms of both molecules are discussed.

Electron impact vibrational excitation of CO in the range 1–4 eV

Abstract The cross sections for resonant vibrational excitation of the CO molecule by electron impact in the range 1–4 eV have been calculated. The calculations have been done on the basis of resonance scattering theory for the vibrational transitions from the ground level as well as from the excited levels.

Superexcited states in the vacuum-ultraviolet photofragmentation of isoxazole molecules

The photofragmentation of isoxazole molecules producing excited atomic and molecular fragments has been investigated over the energy range 16–50 eV, using photon-induced fluorescence spectroscopy. The following fragments have been identified by their fluorescence: the excited hydrogen atoms H(n), n = 3–7 and the diatomic CH(A 2 � , B 2 � − ), CN(B 2 � + ) and C2(d 3 � g) fragments. The diatomic fragments are vibrationally and highly rotationally excited. The fragmentation yield curves for the CH(A 2 � ), CN(B 2 � + ), C2(d 3 � g) and the H(n), n = 3–7 deduced from their emission yields, were obtained in the photon energy ranges from their appearance energies up to 50 eV. It is found that the fragmentation occurs via excitation into higher lying superexcited states of isoxazole. The vertical excitation energies of these states were determined and their possible fragmentation processes are discussed. (Some figures may appear in colour only in the online journal)

Measurements of differential cross sections for elastic electron scattering in the backward direction by molecular oxygen

Absolute differential cross sections have been measured for elastic electron scattering by molecular oxygen in the backward direction over the scattering-angle range 100°–180°, at selected incident energies in the range 7–20 eV. These measurements employed the magnetic angle-changing technique with a newly designed conical-solenoid source for the localized magnetic field. The measured differential cross sections are presented together with previous experimental work and the results of theoretical calculations. Integrated elastic and momentum transfer cross sections have been deduced using the measured differential cross sections for backward scattering together with existing differential cross sections for forward scattering.

A study of electron impact excitation of molecular oxygen at a scattering angle of 180

Abstract Excitation of molecular oxygen by electron impact has been observed at the backward scattering angle of 180°. For these studies a new solenoid system with a conical geometry has been designed to implement the angle-changing technique. Energy loss spectra have been measured to deduce differential cross-sections for vibrational excitation of the X 3 Σ g − ground state and excitation of the a 1 Δ g state at 180°. Excitation of the b 1 Σ g + state has not been observed at 180° in agreement with the theoretically predicted selection rule Σ − ←↦Σ + at that angle.

Excitation of carbon monoxide by electron impact in the 8–17 eV energy range

Abstract The excitation of carbon monoxide by electron impact has been studied in the energy range from 8 to 17 eV using an optical method. The excitation of several states has been detected in the emission spectral range between 180 and 550 nm. Excitation functions for the A 1 Π and a′ 3 Σ + states have been measured in the near-threshold energy region and are compared with recent experimental and theoretical results.