[en] In this thesis, it is presented the results of the research performed in Resonant Raman effect and Raman effect intensified by surface

No abstract available

[en] The complex Kohn method has been used to obtain photoionization cross sections of N₂ leading to the three lowest states of the N₂⁺ ion, (X²Σ_g⁺, A²Π_u Β²Σ_u⁺). The effect of channel coupling and target correlation on both total and differential photoionization cross sections will be discussed. In particular, the level of theory needed to produce reliable cross sections in the ¹Π_u → kΠ_g channel and differential cross sections in the (2σ_u)^-1 ionization channel will be presented

[en] This paper presents an investigation of the stepwise ionization processes which occur during the interaction of laser radiation with electronegative gases. Calculations are carried out adopting a modified version of the electron cascade model previously developed by Evans and Gamal. The modifications of the model are performed for the case of molecular oxygen to account for electron attachment losses. Particular attention is devoted to molecular oxygen at a pressure of 2.8 x 10⁴ Torr irradiated by 10 ns pulse of Nd:YAG laser (λ=1.064 μm) at a peak intensity of 1.7x10¹¹Wcm^-2. The calculations consider the effect of the secondary ionization processes on the electron energy distribution function and its parameters (evolution of the density of the excited molecules, electrons density as well as the electron mean energy during the laser flash). This analysis shows how the removal of slow electrons by attachment to oxygen molecules creates a strong competition between the stepwise ionization processes. These processes namely photoionization and collisional ionization deplete the electronic excited states and contribute eventually to the ionization growth rate in laser induced breakdown of electronegative gases. (author). 7 refs, 6 figs, 1 tab

[en] Topics covered include: negative ion formation in organic molecules; negative-ion formation in Fe(CO)₅ and Ni(CO)₄; collisional ionization of Na, K, and Cs by CO₂, COS, and CS₂, electron affinities; abnormally large electron affinities for some hexafluoride molecules; π-electron affinities for organic molecules; gas phase laser-ion spectroscopy; studies of dissociative ionization by electron impact; ionization potentials of organic donor molecules; reactions of electronically excited atoms; kinetic energy production from unimolecular dissociations; optical and electrical measurements on organic semiconductors; level shifts from coulomb interaction of atoms in a gas; and rotational resonance in low-energy electron-H₂ scattering. 24 figures, 3 tables

[en] The main features of multiphoton processes are described on a somewhat elementary basis. The emphasis is put on multiphoton ionization of atoms where the influence of resonance effects is given through typical examples. The important role played by the coherence of light is shown to produce a very dramatic influence on multiphoton absorption. Different observations concerning molecules, electrons, as well as solid surfaces illustrate the generality of these very non linear interaction between light and matter. (Auth.)

[en] The helium dimer He₂ is an extreme quantum system, bound with only 100 neV of binding energy and a widely smeared wavefunction, showing a mean internuclear di stance of 52 Angstroem. We study the photoionization of this quantum system by me ans of the COLTRIMS technique. We find surprisingly efficient mechanisms by whic h a single photon can lead to ejection of two electrons, one from each of the distant atom of the dimer.

[en] Relationship between statistical properties of laser light scattering in Brownian medium and photon-counting distributions are described in detail. A coherence optical detection has been constructed and by using photon-counting technique the ensemble distribution of the scattered field within space and time coherence has been measured. Good agreement between theory and experiment is shown. (author)

[en] The two=photon ionization probability of a simple model of diatomic molecule has been exactly evaluated under the assumption that a perturbative treatment is valid. The model consists of a simple electron in one-dimensional motion in the field of two fixed Dirac delta wells. The exact results are compared with a number of approximations arising from simplifications introduced at the level of final state and/or the intermediate states involved in the evaluation of the relevant ionization amplitude

[en] Photoionization and photon-induced fragmentation of isomeric icosahedral closo-carboranes by monochromatic synchrotron radiation is reported. Vacuum ultraviolet radiation from the 3 m NIM-I beam line at the storage ring BESSY (Berlin) was used for the experiments. This allows us to measure ionization thresholds and fragmentation patterns at various photon energies. In spite of complexities that result because of the natural isotope abundance of boron and photon-induced loss of hydrogen, the distinct mass spectrometry fragmentation patterns have been partially identified. At low photoionization energies, we find that the loss of atomic hydrogen corresponds to even numbers of hydrogen atoms. Distinct differences between the isomers of closo-dicarbadodecaborane (orthocarborane (1,2-C₂B₁₀H₁₂), metacarborane (1,7-C₂B₁₀H₁₂)), paracarborane (1,12-C₂B₁₀H₁₂) are observed indicating that the loss of pairs of hydrogen depends on the carbon placement within the carborane cage. Furthermore, fragmentation of the cage into singly charged fragments of variable mass is observed along with stable doubly charged intact carborane cages. These results are discussed along with plausible fragmentation mechanisms