Excitation of L-valine molecules by electrons and photons.

Excitation of L-valine molecules was studied by optical spectroscopy. Optical emission spectra of the L-valine molecule and optical excitation functions of molecular bands and the Hß spectral line were measured in the gas phase using electron impact. In the spectra of optical emission in the wavelength range of 250-500 nm, intense emission bands were found at energies of incident electrons of 30, 50 and 70 eV. Analysis of structural features of the valine molecule suggested a fragmentation scheme with the formation of excited particles in collisions with electrons. A notable feature of the presented optical excitation functions is a different growth dynamics with an increase in the energy of exciting electrons and the presence of a number of features and kinks, which are especially pronounced for λ = 305 nm and λ = 311 nm. The excitation thresholds were determined from the initial sections of the excitation functions of the most intense spectral lines by the least-squares method. The photoluminescence spectra of L-valine were measured for the first time on a Shimadzu RF-6000 spectrofluorophotometer in the spectral range of 400-800 nm for excitation wavelengths of 250, 275, 333, 351, and 380 nm.

Surface miller index dependence of Auger neutralization of ions on surfaces.

Neutralization of He+ ions in grazing incidence scattering on Ag(111) and Ag(110) surfaces is studied. These measurements reveal the existence of an order of magnitude difference in the probability of ion survival on Ag(110) and Ag(111). The experimental results are discussed in terms of survival from Auger neutralization, whose rates are derived theoretically. Molecular dynamics simulation of scattered ion trajectories is performed and the surviving ion fractions are then calculated using the theoretical Auger neutralization rates, without adjustable parameters. The calculations agree quite well with the experimental data and show that the observed differences in the neutralization probabilities on these surfaces are related to different extensions of the electron density beyond the surface, resulting from different atomic packing.