Annick Giusti-Suzor

Shape resonance and electronic autoionization in vibrationally resolved partial photoionization cross sections of O2

Vibrationally resolved partial photoionization cross sections of O2 leading to the b4Σ−g and B2Σ−1g(3σ−1g) tonic states have been measured at high resolution in a wide photon energy range from 0.5 eV above threshold to 24.5 eV. The σu shape resonance is observed around 21.5 eV, in fairly good agreement with “one-electron” theoretical predictions. The series of resonances from 19 to 20 5 eV result from an autoionization process with a strong vibrational selectivity, explained by the similar geometries of the resonance states and the b ionic state. The large resonance widths originate from a strong Rydberg-valence orbital mixing Calculations using multichannel quantum defect theory reproduce the most important features.

Above-threshold dissociation of H+2 in intense laser fields.

We present nonperturbative, time-independent calculations of the photodissociation rate of H{sup +}{sub 2} in intense laser fields. The energy distribution of the protons consists in a sequence of peaks evenly spaced by half the photon energy, all of equal width but of varying heights. They result from multiphoton absorption above the dissociation threshold, with equal sharing of the excess photon energy between H and H{sup +}. Surprisingly, the distribution of higher-energy peaks decreases with increasing intensity, due to stimulated free-free emission of the dissociating fragments. We also predict a sharp angular distribution of the protons along the electric field vector of a linearly polarized laser.

COHERENT CONTROL OF PHOTODISSOCIATION IN INTENSE LASER FIELDS

The fragmentation dynamics of the hydrogen molecular ion H2+ and of its isotopic derivate HD+subjected to an intense pulsed laser radiation are studied using quantum wave packet propagations. It is shown that bichromatic optical excitations are subject to a high degree of control through the variation of the relative phase between the two fields. A phase‐locked (ω,2ω) laser pulse is used to induce asymmetry in the angular distribution of the emitted fragments. In addition, an appreciable isotope separation in the fragmentation of HD+ is predicted. The critical role of quantum molecular interferences in such phase‐controllable processes is demonstrated.

Coherent Control of Isotope Separation in HD + Photodissociation by Strong Fields

The photodissociation of the

Associative Ionization: Experiments, Potentials, And Dynamics

{\mathrm{HD}}^{+}

Recent Developments and Perspectives in the Treatment of Dissociative Recombination and Related Processes

molecular ion in intense short-pulsed linearly polarized laser fields is studied using a time-dependent wave-packet approach where molecular rotation is fully included. We show that applying a coherent superposition of the fundamental radiation with its second harmonic can lead to asymmetries in the fragment angular distributions, with significant differences between the hydrogen and deuterium distributions in the long wavelength domain where the permanent dipole is most efficient. This effect is used to induce an appreciable isotope separation.

Molecular dynamics in intense laser fields

Publisher Summary This chapter presents an account of research into fundamental questions, spanning roughly the past decade, and provides continuity from earlier reviews of collisional ionization. The chapter discusses progress along three principal lines: (1) experimental investigation of the fundamental questions, (2) the calculation of molecular potential curves required for the interpretation of experiments, and (3) a review of theoretical approaches developed to grapple with the physics of electron bound-free coupling in heavy particle associative and dissociative processes. The chapter explains the problem of molecular potentials and dynamics of associative ionization. The treatment of associative ionization necessitates knowledge of accurate potential curves and dynamical couplings characterizing the quasi-molecule formed during the collision. Dynamics of associative ionization reviews and classifies the theoretical approaches. It assumes that the basic molecular data, the potential curves and couplings responsible for the ionization process are either known from first principles or have been parametrically fit to experimental results.

Above-threshold dissociation ofH2+in intense laser fields

In 1988, J. B. A. Mitchell and S. L. Guberman decided to gather together near Lake Louise (Ontario) the various people interested in Dissociative Recombination (DR), spread over several domains of research: an important process for laboratory plasmas as well as interstellar and planetary chemistry, this reaction also provides a clue to elementary processes in atoms and molecules since most of the basic interactions between electrons and nuclei, in bound or continuum states, are involved. This meeting gave a real impetus to the field, by initiating several collaborations between experimentalists using different methods, between theoreticians dealing with molecular structure on one hand, dynamics on the other hand; last but not least, between experimentalists and theoreticians. As an example, Table 1 presents most of the theoretical papers on DR (restricted to diatomic molecules), with the “post-Lake Louise” ones in boldface. Clearly, the four last years have been fruitful, and the meeting in Saint-Jacut in May 1992 came at the right time to summarize the recent advances in the field and define the new prospect.

Above-threshold dissociation of H sup + sub 2 in intense laser fields

The fragmentation dynamics of small molecules submitted to intense laser fields can be described in the framework of laser‐assisted multichannel half‐collisions. A number of unexpected features have been observed or predicted in the past few years. We review these processes for the case of the molecular ion H2+. The theoretical results, obtained mostly from time‐dependent wave‐packet calculations, are analyzed in terms of ‘‘dressed’’ potential curves, and compared to available experimental results.

Two-color coherent control of H2+ photodissociation in intense laser fields.

We present nonperturbative, time-independent calculations of the photodissociation rate of H{sup +}{sub 2} in intense laser fields. The energy distribution of the protons consists in a sequence of peaks evenly spaced by half the photon energy, all of equal width but of varying heights. They result from multiphoton absorption above the dissociation threshold, with equal sharing of the excess photon energy between H and H{sup +}. Surprisingly, the distribution of higher-energy peaks decreases with increasing intensity, due to stimulated free-free emission of the dissociating fragments. We also predict a sharp angular distribution of the protons along the electric field vector of a linearly polarized laser.