The mass spectrum of positive ions formed by electron impact ionization of guanine (C5H5N5O) has been measured in a crossed electron–molecule beam experiment. The ionization energy of the molecule and the appearance potential (AP) of some fragment ions were obtained. The value of the ionization energy for the parent ion with m/z = 151 was determined experimentally to be 8.1 ± 0.2 eV, and it is in good agreement with vertical ionization energies obtained in previous photoelectron spectroscopy experiments. The temperature effect for the APs of guanine has been studied for the first time, and a remarkable difference of the APs for various fragment ions has been observed.
The ionization efficiency curve up to 16 eV, the total electron
scattering cross section up to 15 eV, the electron excitation
cross sections for metastable 5 3P0,1,2 and
resonance 5 1P1 levels up to 11 eV have been
measured for cadmium atoms. The energy dependence of the total
cross section has revealed two distinctly well resolved
resonance features at energies of 0.33 and 3.74 eV,
respectively. The total excitation cross sections measured for
the 5 3P0,1,2 and 5 1P1 levels refine the earlier measured optical excitation functions for these levels. These results show the possibility of measuring, in
the same experiment, the total cross section of electron
scattering by cadmium atoms, the ionization efficiency and the low-lying
level excitation function, as well as providing their absolute
calibration.
In electron spectroscopy a wide variety of methods using the dispersive properties of both magnetic and electric fields are applied to analyse the energies of charged particles moving in a longitudinal magnetic field. Retarding potential analysers where a uniform magnetic field is used, however, possess a disadvantage: an integral characteristic (retarding curve) must be differentiated in order to determine the energy spectrum. In analysers with a non-uniform magnetic field (which is increased or decreased in the retarding region), electrons are analysed by both the longitudinal and total components of electron velocity. The method of using a Wien filter with non-uniform transverse fields, immersed in a weak longitudinal magnetic field, has also been reported. A complicated system of magnetic field formation of these analysers is coupled with restrictions on the magnetic field alteration rate. Trochoidal electron monochromators (TEMs) have a favourable advantage-principle simplicity-enabling low-energy electron beams to be obtained. Since being created, the TEM has been used in a series of studies of electron scattering by atoms and molecules and solid surfaces. The monochromator theory has been considered in detail in the literature where the principal parameters of the TEM were calculated. Here we consider the influence of transverse potential drop at the entrance slit and suggest the minimization of beam distortion at the exit by means of the proper choice of non-uniform transverse electric field parameters.
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