A classical Over Barrier Model to compute charge exchange between ions and one-optical-electron atoms

In this paper we study theoretically the process of electron capture between one-optical-electron atoms (e.g. hydrogenlike or alkali atoms) and ions at low-to-medium impact velocities (v/v_e <= 1) working on a modification of an already developed classical Over Barrier Model (OBM) [V. Ostrovsky, J. Phys. B: At. Mol. Opt. Phys. {\bf 28} 3901 (1995)], which allows to give a semianalytical formula for the cross sections. The model is discussed and then applied to a number of test cases including experimental data as well as data coming from other sophisticated numerical simulations. It is found that the accuracy of the model, with the suggested corrections and applied to quite different situations, is rather high.Comment: 12 pages REVTEX, 5 EPSF figures, submitted to Phys Rev

Circular dichroism in molecular frame photoelectron emission from space fixed oriented molecules : a complete experiment with a single circular polarization of the light

International audienc

Electron-ion vector correlations for the study of photoionization of molecules in the UVX range: From synchrotron radiation to short light pulses

Molecular frame photoemission is a very sensitive probe of the photoionization (PI) dynamics of molecules. The electron-ion vector correlation (VC) method takes advantage of dissociative photoionization (DPI) reactions of small molecules to measure such observables. It relies on the coincident detection of the photoelectron and the ion fragment emitted from the same DPI event and the determination of their velocity vectors. Most of the VC studies so far have been performed using synchrotron radiation (SR) light sources which benefit from a high repetition rate (1–10 MHz) favorable for coincidence experiments. In this paper we discuss the extension of this method to the study of PI processes induced by ultra-short VUV light sources, which provide the capability for investigating processes characterized by femtosecond or subfemtosecond dynamics. We first illustrate the VC method by the report of recent results of a comparative study of resonant photoionization of the H2 and D2 molecules induced by VUV circularly polarized synchrotron radiation at SOLEIL in the region involving resonant excitation of Q1 and Q2 doubly excited state series. This problem is of particular interest since autoionization and dissociation of selected Q1 or Q2 states occur on a comparable time scale of few femtoseconds, which implies a coupling between the electronic and nuclear motion. The extension of the VC method using femtosecond laser sources is then demonstrated by results for multiphoton PI of the Xe atom induced by 70 fs pulses centered at 400 nm delivered by the SOFOCKLE and PLFA sources (SLIC, CEA-Saclay) after frequency doubling of a 1 kHz Ti:sapphire laser

Molecular frame and recoil frame photoelectron angular distributions from dissociative photoionization of NO2

The authors report measured and computed molecular frame photoelectron angular distributions (MFPADs) and recoil frame photoelectron angular distributions (RFPADs) for the single photon ionization of the nonlinear molecule NO(2) leading to the (1a(2))(-1) b (3)A(2) and (4a(1))(-1) (3)A(1) states of NO(2)(+). Experimentally, the RFPADs were obtained using the vector correlation approach applied to the dissociative photoionization (DPI) involving these molecular ionic states. The polar and azimuthal angle dependences of the photoelectron angular distributions are measured relative to the reference frame provided by the ion recoil axis and direction of polarization of the linearly polarized light. Experimental results are reported for the photon excitation energies h nu=14.4 and 22.0 eV. Theoretically the authors give expressions for both the MFPAD and the RFPAD. They show that the functional form in the recoil frame, where an average over the azimuthal dependence of the molecular fragments about the recoil direction is made, is identical to that they have earlier found for the DPI experiments performed on linear molecules. MFPADs were then computed using single-center expansion techniques within the fixed-nuclei frozen-core Hartree-Fock approximation. The computed cross sections for ionization to the (1a(2))(-1) b (3)A(2) state show a strong propensity for ionization with the polarization of the light perpendicular to the plane of the molecule, whereas the ionization to the (4a(1))(-1) (3)A(1) state of the ion is of similar intensity for all orientations of the polarization of the light in the molecular frame. These qualitative features of the MFPAD are also evident in the RFPAD. The RFPAD for ionization leading to the (1a(2))(-1) b (3)A(2) state is strongly peaked in the perpendicular orientation, whereas the RFPAD for ionization leading to the (4a(2))(-1) (3)A(1) state is much more nearly isotropic. Comparison between experimental and theoretical RFPADs indicates that the recoil angle for NO(+) fragments is similar to 50 degrees relative to the symmetry axis of the initial C(2v) symmetry of the NO(2) molecule in the ionization leading to the (1a(2))(-1) b (3)A(2) state and the recoil angle is similar to 120 degrees for the O(+) fragment for ionization leading to the (4a(1))(-1) (3)A(1) state. (c) 2007 American Institute of Physics