Complete photo-fragmentation of the deuterium molecule

Abstract

However, despite 80 years of theoretical attention, near exact calculations for such systems are only available for bound states. On the experimental side, the tests of these calculations are largely based upon level energies or single particle momentum 3 distributions. Very promising and challenging new classes of experiments are those which achieve a complete description of the outcome following the excitation of the ground state to an unbound continuum. The momenta, i.e. the set of vectors, of all the fragments of an atom or molecule break-up can be measured in coincidence with high precision using state-of-the-art imaging and timing techniques [16]. These asymptotic many-particle momentum distributions are determined by the interaction inducing the fragmentation, the bound initial state from which it emerged, and the interactions between the outgoing particles. Thus it is useful to the experimentalist to keep the interaction process as simple as possible and to choose a geometry where final state interactions are negligible or under control. In the present study we used the absorption of a single photon to fragment the deuterium molecule: hν + D 2 → 2 e -+ 2 d + Due to their heavy masses, the initial motion of the nuclei in the continuum can be assumed the same as in the ground state at the instant of the electronic transition (Born Oppenheimer approximation). Once the electrons have left the system, the motion of the nuclei is solely determined by their Coulomb repulsion; they accelerate to a Kinetic Energy Release (KER) which corresponds to the Coulomb potential associated with their initial separation. Quantum mechanically one maps the nuclear vibrational wave-function onto the Coulomb potential to yield a KER spectrum. Inverting this process determines the squared nuclear vibrational wave-function from the measured KER spectrum [17]. Furthermore, by selecting events that occur within a fixed subregion in the KER spectrum, one samples molecules for which the corresponding internuclear distance is defined much more precisely than the full extent of the initial nuclear wave-function. This allows us to show how the electronic continuum momentum distribution depends on the inter-nuclear separation in the molecule and its orientation with respect to the photon polarization. [18,19,20,21]. In brief, inside our momentum spectrometer, a supersonic D 2 -gas jet was crossed with the linear polarized photon beam from the LBNL Advanced Light Source (D 2 provides a higher target density than a comparable H 2 gas jet and data less contaminated by random coincidences from background H 2 O). The electrons and ions created in the intersection of the photons with

Hydrogen and fluorine migration in photo-double-ionization of 1,1-difluoroethylene (1,1-C2H2F2Gaire1, Bocharova2, Sturm3 et al. 2014Phys. Rev. ASelf Cite41130View full textAdd to dashboardCite

“…In the indirect process (sometimes also referred to as a sequential process), photoejection of one electron leads to an intermediate cation state, which later decays by autoionization or other processes (e.g., Auger decay, fluorescence, etc.). After a couple of decades of studying the PDI of simple atoms and diatomic molecules (e.g., He, H 2 , N 2 , CO) in great detail [2][3][4][5][6][7][8][9][10], the investigation has been extended to polyatomic molecules in order to gain a general understanding of the double-ionization process in more complex systems. Simple hydrocarbon molecules are an ideal testbed for a series of studies with increasing complexity.…”

Single and triple differential cross sections for double photoionization ofH−

“…Recent experimental investigations have focused on double photoionization (DPI) of two-electron atoms [1][2][3][4][5][6][7] and molecules [8][9][10][11] as a sensitive probe of the correlated motion of electrons. The DPI problem is interesting from both experimental and theoretical viewpoints because the process by which an atom or molecule absorbs a photon of sufficient energy to eject two electrons into the continuum necessarily depends on electron correlation.…”

Molecular ionization and dissociation using synchrotron radiation and ultrashort laser pulses

“…Experiments in which both electrons are ejected from an oriented hydrogen molecule by absorption of a single photon are currently available [9,[71][72][73]. Among the latter, Weber et al [9,72] have recently demonstrated that the ejection pattern of the electrons depends sensitively on the bond distance between the two nuclei as they vibrate in their ground state.…”

“…Among the latter, Weber et al [9,72] have recently demonstrated that the ejection pattern of the electrons depends sensitively on the bond distance between the two nuclei as they vibrate in their ground state. In the experiments, linearly polarized 75 eV synchrotron radiation was used to study single-photon induced fragmentation of molecular deuterium.…”

“…In early pictures of molecular ionization, the nuclear motion was either ignored or described in terms of the Franck-Condon (FC) approximation, in which electronic processes occurring at the equilibrium position of the nuclei are weighted by the squared overlap between the initial and final vibrational states. With the advent of kinematically complete experiments [3,4], in which the momenta of all charged particles is determined, new phenomena with an intrinsic molecular origin have been discovered (see, e.g., [5][6][7][8][9][10][11]). Also the above pictures have been revealed to be incomplete.…”