Circular Dichroism in Photoionization ofH2

The presence of net circular dichroism in the photoionization of nonchiral homonuclear molecules has been put in evidence recently through the measurement of molecular-frame photoelectron angular distributions in dissociative photoionization of H 2 [Dowek et al., Phys. Rev. Lett. 104, 233003 (2010)]. In this work we present a detailed study of circular dichroism in the photoelectron angular distributions of H 2 and D 2 molecules, oriented perpendicularly to the propagation vector of the circularly polarized light, at different photon energies (20, 27, and 32.5 eV). Circular dichroism in the angular distributions at 20 and to a large extent 27 eV exhibits the usual pattern in which inversion symmetry is preserved. In contrast, at 32.5 eV, the inversion symmetry breaks down, which eventually leads to total circular dichroism after integration over the polar emission angle. Time-dependent ab initio calculations support and explain the observed results for H 2 in terms of quantum interferences between direct photoionization and delayed autoionization from the Q 1 and Q 2 doubly excited states into ionic states (1sσ g and 2pσ u) of different inversion symmetry. Nevertheless, for D 2 at 32.5 eV, there is a particular case where theory and experiment disagree in the magnitude of the symmetry breaking: when D + ions are produced with an energy of around 5 eV. This reflects the subleties associated to such simple molecules when exposed to this fine scrutiny.

Physical Review A, 2019

Photoelectron circular dichroism results from one-photon ionization of chiral molecules by circularly polarized light and manifests itself in forward-backward asymmetry of electron emission in the direction orthogonal to the light polarization plane. What is the physical mechanism underlying asymmetric electron ejection? How "which way" information builds up in a chiral molecule and maps into forward-backward asymmetry? We introduce instances of bound chiral wave functions resulting from stationary superpositions of states in a hydrogen atom and use them to show that the chiral response in one-photon ionization of aligned molecular ensembles originates from two propensity rules: (i) Sensitivity of ionization to the sense of electron rotation in the polarization plane. (ii) Sensitivity of ionization to the direction of charge displacement or stationary current orthogonal to the polarization plane. In the companion paper [1] we show how the ideas presented here are part of a broader picture valid for all chiral molecules and arbitrary degrees of molecular alignment.

Physical Review Letters, 2019

Dichroism in double photoionization of H 2 molecules by elliptically polarized extreme ultraviolet pulses is formulated analytically as a sum of atomiclike dichroism (AD) and molecular symmetry-mixed dichroism (MSMD) terms. The MSMD originates from an interplay of 1 Σ þ u and 1 Π þ u continuum molecular ionization amplitudes. For detection geometries in which the AD vanishes, numerical results for the sixfold differential probabilities for opposite pulse helicities show that the MSMD is significant in the electron momentum and angular distributions and is controllable by the ellipticity.

Vacuum, 1990

A new phenomenon in photoemission from adsorbates is reported. With circularly polarized synchrotron radiation and a special observation geometry (defining a ‘handedness’ of the directions of photon impact, electron ejection and surface normal) photoemission intensity asymmetries arise upon reversal of photon helicity. Circular Dichroism in the Angular Distribution of photoelectrons (CDAD) has been theoretically predicted in the pure electric dipole approximation. The phenomenon should occur for all molecular adsorbates which are spatially oriented. First experimental results for a diatomic molecule (CO), a polyatomic molecule (benzene) and a molecule with significant spin-orbit interaction (CH3l) revealed CDAD asymmetries in all the photoemission signals corresponding to the various molecular orbitals.

Nature Communications, 2013

Electron-nuclei coupling accompanying excitation and relaxation processes is a fascinating phenomenon in molecular dynamics. A striking and unexpected example of such coupling is presented here in the context of photoelectron circular dichroism measurements on randomly oriented, chiral methyloxirane molecules, unaffected by any continuum resonance. Here, we report that the forward-backward asymmetry in the electron angular distribution, with respect to the photon axis, which is associated with photoelectron circular dichroism can surprisingly reverse direction according to the ion vibrational mode excited. This vibrational dependence represents a clear breakdown of the usual Franck-Condon assumption, ascribed to the enhanced sensitivity of photoelectron circular dichroism (compared with other observables like cross-sections or the conventional anisotropy parameter-b) to the scattering phase off the chiral molecular potential, inducing a dependence on the nuclear geometry sampled in the photoionization process. Important consequences for the interpretation of such dichroism measurements within analytical contexts are discussed.

Physical Review Letters, 1992

The photoionization process NO A2Z+(c =0, N=22) NO+ X'Z+(v+=0, lV+)+e is studied with suScient energy resolution that the photoelectron angular distributions associated with individual rotational levels N+ of the ion are determined. By ionizing with left and right circularly polarized light and observing the change in the rotationally resolved photoelectron angular distributions, we can deduce all dynamical information, including the signs of the relative phase shifts of the photoelectron partial waves. This information constitutes the first complete description of the photoionization of a molecule.

Nature Physics, 2018

Zeitschrift f�r Physik D Atoms, Molecules and Clusters, 1997

This paper developes a theoretical framework for one-photon, electric dipole ionization of molecules, prepared in a single |JKM rotational state of their ground electronic motion using a hexapole electrostatic field followed by a weak and homogeneous orienting electric field E, by taking also the |J K M eigenstate of the residual photoion into account. This theory has been used to study photoionization in a generic C 3v molecule by the linearly as well as circularly polarized light. Integrated and differential photocurrents plus circular dichroism, obtained from a model calculation, for ionization in two different experimental configurations in 13a 2 1 orbital of a state selected and oriented CH 3 I are discussed. These results show, among other things, that somewhat different propensity rules for |JKM → |J K M transitions are obeyed in different experimental geometries. Also, dichroic effect exists in the photoelectron angular distribution when circularly polarized light is incident perpendicular to E.

Physical review. B, Condensed matter, 1994

Physical Review A, 2009

Photoelectron angular distributions from fixed-in-space H 2 molecules exposed to ultrashort xuv laser pulses have been evaluated. The theoretical method is based on the solution of the time-dependent Schrödinger equation in a basis of stationary states that include all electronic and vibrational degrees of freedom. Asymmetric angular distributions are observed as a consequence of the delayed ionization from the H 2 doubly excited states, which induces interferences between gerade and ungerade ionization channels. The analysis of this asymmetry as a function of pulse duration can provide an estimate of the corresponding autoionization widths.