Excitation of lowest electronic states of the uracil molecule by slow electrons

The excitation of lowest electronic states of the uracil molecule in the gas phase has been studied by electron energy loss spectroscopy. Along with excitation of lowest singlet states, excitation of two lowest triplet states at 3.75 and 4.76 eV (±0.05 eV) and vibrational excitation of the molecule in two resonant ranges (1?C2 and 3?C4 eV) have been observed for the first time. The peak of the excitation band related to the lowest singlet state (5.50 eV) is found to be blueshifted by 0.4 eV in comparison with the optical absorption spectroscopy data. The threshold excitation spectra have been measured for the first time, with detection of electrons inelastically scattered by an angle of 180°. These spectra exhibit clear separation of the 5.50-eV-wide band into two bands, which are due to the excitation of the triplet 1³ A?? and singlet 1¹ A?? states.     

Excitation of adenine molecules by slow electrons

The excitation of adenine molecules in the gas phase by slow electrons is studied by optical spectroscopy. The emission spectra of the molecule in the region of 250–500 nm upon excitation by slow electrons in the energy range of 15–120 eV, as well as the optical excitation functions of the most intense emission bands, are presented.     

Excitation cross section for iridium atoms by slow electrons

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 5, pp. 711–716, May, 1991.     

Excitation of quintet levels of the ytterbium atom by slow electrons

The excitation of transitions from upper quintet levels of the ytterbium atom is studied by the method of extended crossing beams. Seventy-five cross sections are measured at the excitation electron energy of 50 eV. Twelve optical excitation functions are recorded in the electron energy range from 0 to 200 eV.     

Excitation of resonance transitions in a thulium atom by slow electrons

We experimentally studied the excitation of resonance transitions in a thulium atom in electron-atom collisions. At an electron energy of 50 eV, we measured 52 TmI excitation cross sections. We recorded 41 optical excitation functions in the electron energy range from the excitation threshold to 200 eV. The measured cross sections are, on average, a factor of 1.09 larger than their preceding experimental values but a factor of 2.41 smaller than their theoretical values.     

Excitation cross-sections of 3 F-and 3 F o-levels of barium atom by slow electrons

Excitation of the ³F-and ³F^o-levels of barium atom by slow electrons has been investigated experimentally. A total of 75 excitation cross-sections were measured at 30-eV electron energy; 20 optical excitation functions, in the range 0–200 eV electron energy. The behavior of cross-sections in some spectral series of BaI is discussed. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 757–762, November–December, 2008.     

Formation of positive and negative ions of thymine molecules under the action of slow electrons

The formation of positive and negative molecules of thymine—a base of nucleic acids—under the action of slow electrons is investigated by the method of crossed electron and molecular beams. The method developed makes it possible to measure the molecular beam intensity and determine the energy dependences and absolute values of total cross sections for the formation of positive and negative ions of thymine molecules. It is found that the maximal cross section for the formation of positive ions is reached at an energy of 95 eV and its absolute value is, accordingly, 1.4 × 10^?15 cm². The total cross section for the formation of negative ions is 8.2 × 10^–18 cm² at an energy of 1.1 eV. The mass spectra of thymine molecules are measured and the cross sections of dissociative ionization are determined.     

Scattering of slow electrons by Si

The close coupling method is applied to e-Si scattering using Hartree-Fock target wavefunctions. Scattering cross-sections are found to be free from the effects of shape resonances and large elastic cross-sections are obtained at low energies.     

Low-lying electronic states of LiF molecule with inner electrons correlation

The potential energy curves and dipole moments of the low-lying electronic states of LiF molecule are performed by using highly accurate multi-reference configuration interaction with Awcv5z basis sets. 1s, the inner shell of Li is considered as the closed orbit, which is used to characterise the spectroscopic properties of a manifold of singlet and triplet states. 16 electronic states correlate with two lowest dissociation channels Li(²S)+F(²P) and Li(²P)+F(²P) are investigated. Spectroscopic parameters of the ground state X¹Σ⁺ have been evaluated and critically compared with the available experimental values and the other theoretical data. However, spectroscopic parameters of 1³Π, 1¹Δ, 1¹Σ^?, 1¹Π, 1³Σ⁺, 2³Σ⁺, 1³Δ, 1³Σ^?, 2³Π, 2¹Π, 3³Π, 3¹Π and 3³Σ⁺ states are studied for the first time. These 13 excited states have shallow potential wells, and the dispersion coefficients of these excited states are predicted. In additional, oscillator strengths of excited states at equilibrium distances are also predicted.     

Low-lying electronic states of BeH+ with the effect of inner electrons

The potential energy curves of the low-lying electronic states of BeH⁺ molecular ion are performed by using highly accurate multi-reference configuration interaction with AV5Z basis sets for H atom and ACV5Z basis set for Be atom, 1s inner shell of Be is considered as the core orbit and the active orbit, respectively, which are used to characterise the spectroscopic properties of a manifold of singlet and triplet states. Fourteen electronic states correlated with eight dissociation channels are investigated, we have found that the a³Σ⁺ and c³Σ⁺ both are bound states, the 3³Σ⁺ possesses double wells, and the C¹Σ⁺, 3³Σ⁺, 2³Π, 2¹Π, 1¹Δ, 1³Δ, 2³Δ and 2¹Δ states are studied for the first time. Transition dipole moment, Franck–Condon factors q_υ′υ^″ and Einstein coefficients A_υ′υ^″ for A¹Σ⁺–X¹Σ⁺, 2¹Π–B¹Π, c³Σ⁺–a³Σ⁺ and b³Π–a³Σ⁺ systems have been calculated. Radiative lifetime of A¹Σ⁺–X¹Σ⁺ band system has also been determined.     

Inelastic scattering of slow electrons by lanthanum oxide

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 6, pp. 988–993, December, 1991.     

Microscopy with slow electrons

Low energy microscopy is treated as the low energy limit of electron microscopy as a whole in all its basic branches, i.e. the emission, transmission and scanning microscopies. The instrumental and methodological aspects are briefly discussed. These include the interaction of electrons with a solid, the contrast formation mechanisms, the instrumentation problems and actual progress achieved in all three microscopies, from the point of view of lowering the energy of electrons, impacting or leaving the specimen, down to the low energy range below 5 keV and the very low energy range below 50 eV.Invited lecture presented at the Seminar on Secondary Electrons in Electron Spectroscopy, Microscopy, and Microanalysis, Chlum (The Czech Republic), 21–24 September 1993.     

Threshold vibrational excitation of CO2 by slow electrons

Threshold structures, reminiscent of those seen in the polar hydrogen halides, have recently been observed in the cross sections for electron impact excitation of certain vibrational levels of the nonpolar CO2 molecule. These structures occur at energies outside the range where shape resonances dominate the dynamics. We propose a virtual state model that describes the multidimensional nuclear dynamics during the collision and explains quantitatively the selectivity observed in the excitation of the Fermi dyad, as well as the pattern of threshold peaks and oscillations seen in the upper levels of the higher polyads.     

Theoretical study of the transition probabilities among the three lowest electronic states of the SeS molecule

Spin-perturbed CI wavefunctions are reported for the X ³Σ^? electronic states of the SeS molecule. The Breit-Pauli approach is employed using the one- and two-electron spin-orbit operator as the perturbing hamiltonian and a zeroeth-order basis of CI eigenfunctions generated by the standard multireference single- and double-excitation (MRD-CI) formalism. Transition moments are reported between each of the above states for electric and magnetic dipole and electric quadrupole radiative processes, and these results are compared with recent experimental high resolution data obtained by Fink, Kruse, Ramsay and Wang. Generally good agreement is found between computed and observed ratios of such quantities, but the absolute values of the computed transition moments are uniformly found to be only somewhat less than half as large as the corresponding observed results. A simple formula is presented which relates the magnetic moments of the b ¹Σ⁺-X ³Σ1? transitions to twice the square root of the ratio of two observable energy differences and this result promises to be useful in future experimental studies attempting to estimate line strengths for this type of band system. On this basis arguments are also presented supporting the view that the computed absolute intensities may be more accurate than would appear from the original experimental assessment of the SeS spectroscopic data.     

Excitation of surface plasmons by electrons in a parabolic beam

A theory is presented for the excitation of surface plasmons by an electron beam following a non-touching path above a metal surface in Born approximation. The metal is assumed to possess only surface plasmon excitations. Configurations involving deflection of the electron beam in a parallel plate condensor, and by scattering from a field emission tip are envisaged. The relation between experimental conditions and the validity of the semiclassical approximation is discussed. The region of space above the surface in which scattering occurs is calculated, but the feasability of the experiment depends on electron optical factors which are outlined.     

Scattering of electrons in image-potential states by steps

Image-potential states on several stepped copper surfaces were studied by time, energy, and angle-resolved two-photon photoelectron spectroscopy. For different step densities binding energies and effective masses were determined in the energy-resolved and decay rates in the time-resolved mode of two-photon photoemission. The asymmetry with respect to the electron motion up or down the steps of the total decay rates is enhanced for less-ordered step arrangements. Elastic interband scattering strongly depends on details of the backfolding of the bands by the periodic step structure. Elastic intraband scattering is of similar importance as inelastic decay may contribute significantly to the asymmetry of the decay rates. PACS 73.20.At; 79.60.Bm; 72.10.Fk