The hydrogen molecule under the reaction microscope: single photon double ionization at maximum cross section and threshold (doubly differential cross sections)

Abstract

We studied the photo double ionization of hydrogen molecules in the threshold region (50 eV) and the complete photo fragmentation of deuterium molecules at maximum cross section (75 eV) with single photons (linearly polarized) from the Advanced Light Source, using the reaction microscope imaging technique. The 3D-momentum vectors of two recoiling ions and up to two electrons were measured in coincidence. We present the kinetic energy sharing between the electrons and ions, the relative electron momenta, the azimuthal, and polar angular distributions of the electrons in the body fixed frame. We also present the dependency of the kinetic energy release in the Coulomb explosion of the two nuclei on the electron emission patterns. We find that the electronic emission in the body-fixed frame is strongly influenced by the orientation of the molecular axis to the polarization vector and the internuclear distance as well as the electronic energy sharing. Traces of a possible breakdown of the Born-Oppenheimer approximation are observed near threshold.

Role of initial-state electron correlation in one-photon double ionization of atoms and molecules

“…The two ejected electrons must share the energy of a single photon, but the operator for interaction of the electrons with the electromagnetic field is a one-body operator, which for the conditions of most experiments is simply the dipole operator. This fact strongly suggests that the dynamics of double photoejection are correlated, and that expectation has been verified by a large number of experimental measurements showing strong correlation in the angular dependence of the two ejected electrons in double photoionization of both atoms [1][2][3][4][5][6][7][8][9] and molecules [10][11][12][13][14][15][16][17][18][19], only a selection of which we cite here.…”

“…In molecular targets, the sensitivity to electron correlation in double photoionization is by far best revealed by measurements in the molecular frame [11][12][13][14][15][16][17][18], and for that reason we have limited ourselves here to the exploration of this question to oriented molecules. While those measurements thus far have been almost exclusively limited to the cases of the H 2 and D 2 molecules, this study suggests that double photoionization experiments on other oriented molecules will contain strong signatures of initial state correlation in molecular bonds of more complicated systems.…”

Dissociation dynamics of the water dication following one-photon double ionization. I. Theory

“…For that reason, one-photon double ionization is the focus of an extensive literature, of which a small sample includes experimental studies on atoms [1][2][3][4][5][6][7][8][9] and molecules [10][11][12][13][14][15][16][17][18][19] and theoretical studies on atoms that form the basis for theoretical treatments of the more challenging single-photon double photoionization from molecules [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56]. In molecular targets, the physics of double photoionization and, in particular, its sensitivity to the role of electron correlation, is by far best revealed by measurements in the molecular frame [11][12][13][14][15][16][17][18], with no averaging over orientations of the molecule, but those measurements have been almost exclusively limited to the cases of the H 2 and D 2 molecules. One-photon double photoionization of H 2 is followed promptly by the Coulomb explosion of the H ++ 2 dication, and a coincidence measurement of the momenta of the two ejected electrons and one of the protons (together with momentum conservation...…”