Thomas N. Rescigno

Ultrafast Probing of Core Hole Localization in N2

Although valence electrons are clearly delocalized in molecular bonding frameworks, chemists and physicists have long debated the question of whether the core vacancy created in a homonuclear diatomic molecule by absorption of a single x-ray photon is localized on one atom or delocalized over both. We have been able to clarify this question with an experiment that uses Auger electron angular emission patterns from molecular nitrogen after inner-shell ionization as an ultrafast probe of hole localization. The experiment, along with the accompanying theory, shows that observation of symmetry breaking (localization) or preservation (delocalization) depends on how the quantum entangled Bell state created by Auger decay is detected by the measurement.

Complete Photo-Induced Breakup of the H2 Molecule as a Probe of Molecular Electron Correlation

Despite decades of progress in quantum mechanics, electron correlation effects are still only partially understood. Experiments in which both electrons are ejected from an oriented hydrogen molecule by absorption of a single photon have recently demonstrated a puzzling phenomenon: The ejection pattern of the electrons depends sensitively on the bond distance between the two nuclei as they vibrate in their ground state. Here, we report a complete numerical solution of the Schrödinger equation for the double photoionization of H2. The results suggest that the distribution of photoelectrons emitted from aligned molecules reflects electron correlation effects that are purely molecular in origin.

Elastic scattering of low-energy electrons by tetrahydrofuran

We present the results of ab initio calculations for elasticelectron scattering by tetrahydrofuran (THF) using the complex Kohnvariational method. We carried out fixed-nuclei calculations at theequilibrium geometry of the target molecule for incident electronenergies up to 20 eV. The calculated momentum transfer cross sectionsclearly reveal the presence of broad shape resonance behavior in the 8-10eV energy range, in agreement with recent experiments. The calculateddifferential cross sections at 20 eV, which include the effects of thelong-range electron-dipole interaction, are alsofound to be in agreementwith the most recent experimental findings.

Dissociative electron attachment to the H2O molecule II: nucleardynamics on coupled electronic surfaces within the local complexpotential model

Dissociative electron attachment to the H 2 O molecule II: nuclear dynamics on coupled electronic surfaces within the local complex potential model Daniel J. Haxton, 1, 2, ∗ T. N. Rescigno, 2 and C. W. McCurdy 2, 3 Department of Chemistry, University of California, Berkeley, California 94720 Lawrence Berkeley National Laboratory, Chemical Sciences, Berkeley, California 94720 Departments of Applied Science and Chemistry, University of California, Davis, California 95616 We report the results of a first-principles study of dissociative electron attachment (DEA) to H 2 O. The cross sections were obtained from nuclear dynamics calculations carried out in full dimen- sionality within the local complex potential model by using the multi-configuration time-dependent Hartree method. The calculations employ our previously obtained global, complex-valued, potential energy surfaces for the three ( 2 B 1 , 2 A 1 , and 2 B 2 ) electronic Feshbach resonances involved in this process. These three metastable states of H 2 O − undergo several degeneracies, and we incorporate both the Renner-Teller coupling between the 2 B 1 and 2 A 1 states, as well as the conical intersection between the 2 A 1 and 2 B 2 states, into our treatment. The nuclear dynamics are inherently multi- dimensional and involve branching between different final product arrangments as well as extensive excitation of the diatomic fragment. Our results successfully mirror the qualitative features of the major fragment channels observed, but are less successful in reproducing the available results for some of the minor channels. We comment on the applicability of the local complex potential model to such a complicated resonant system. I. INTRODUCTION In the preceeding paper [1], referred to hereafter as (I), we presented global representations of the three ( 2 B 1 , A 1 , and 2 B 2 ) complex-valued potential energy surfaces of the metastable states of H 2 O − which underlie disso- ciative electron attachment to water. This paper is con- cerned with the calculation of the cross sections for that physical process. Prior experimental and theoretical re- sults [2–20] have characterized the various breakup chan- nels and determined the spatial symmetries of the three metastable electronic states of H 2 O − , the 2 B 1 , 2 A 1 , and B 2 electronic Feshbach resonances, which are respon- sible for production of H − and O − . As explained in ref. [18] and (I), the energetically lowest H + OH − chan- nel does not directly correlate with any of the three Fesh- bach states. We therefore conclude that OH − production must be due to nonadiabatic effects. We pursue this problem theoretically using a coupled Born-Oppenheimer treatment of the nuclear motion. The first task, which was described in (I), is the construc- tion of three-dimensional, complex-valued potential en- ergy surfaces for these three states, which have a negative imaginary component due to the finite probability of elec- tron autodetachment back to H 2 O + e − . These complex- valued potential energy surfaces, which are functions of the nuclear geometry q, are defined as V (q) = E R (q) − i Γ(q) where E R is the resonance position and Γ is the width ∗ Present address: Department of Physics and JILA, University of Colorado, Boulder Colorado 80309 of the resonance, which is related to the lifetime by τ = 1/Γ. (We use atomic units throughout this paper.) The present article, which we label (II), is concerned with the use of these potential curves within the local complex potential (LCP) model [21–25] to calculate the nuclear dynamics leading to dissociation. The analysis of the dynamics yields the DEA cross section as a function of incident electron energy. We must account for two major nonadiabatic physical effects in calculating the quantum dynamics of the nuclei. As described in (I), the three potential energy surfaces have several degeneracies which lead to coupling among them. First, the 2 B 1 and 2 A 1 states become members of a degenerate 2 Π pair in linear geometry, and for this rea- son there will be Renner-Teller coupling between them. We expect this coupling to be relevant for DEA via the A 1 state, because the gradient of its potential energy surface will cause the system to move towards linear ge- ometry after the electron attaches. Second, there is a conical intersection [18] between the 2 B 2 and 2 A 1 states which leads to coupling between them. For this reason, as described in (I) we constructed a set of diabatic 2 B 2 and 2 A 1 surfaces, along with a coupling term, which we use in the calculations presented in this paper. In Fig. 1, we show the real parts E R of the constructed potential energy surfaces along a two-dimensional cut which includes the equilibrium geometry of the neutral (r 1 = r 2 = 1.81a 0 ; θ HOH = 104.5 ◦ ). The degenera- cies which lead to the nonadiabatic effects listed above can be seen in this figure. The two-dimensional cut depicted is that for which the two OH bond lengths are equal (r 1 = r 2 ), corresponding to C 2v symmetry. (In C 2v symmetry, the adiabatic and diabatic 2 A 1 and B 2 surfaces coincide.) The backside of this cut lies at r 1 = r 2 = 1.81a 0 , which is the equilibrium value of the bond lengths in neutral H 2 O, and is marked with

Fragmentation pathways for selected electronic states of the acetylene dication

Coincident measurement of the Auger electron and fragment ion momenta emitted after carbon core-level photoionization of acetylene has yielded new understanding of how the dication fragments. Ab initio calculations and experimental data, including body-frame Auger angular distributions, are used to identify the parent electronic states and together yield a comprehensive map of the dissociation pathways which include surface crossings and barriers to direct dissociation. The Auger angular distributions for certain breakup channels show evidence of core–hole localization. (Some figures in this article are in colour only in the electronic version)

Cross sections for short pulse single and double ionization of helium

In a previous publication, procedures were proposed for unambiguously extracting amplitudes for single and double ionization from a time-dependent wavepacket by effectively propagating for an infinite time following a radiation pulse. Here we demonstrate the accuracy and utility of those methods for describing two-photon single and one-photon double ionization of helium. In particular it is shown how narrow features corresponding to autoionizing states are easily resolved with these methods.

Probing autoionizing states of molecular oxygen with XUV transient absorption: Electronic-symmetry-dependent line shapes and laser-induced modifications

U. S. Army Research Laboratory; U. S. Army Research Office [W911NF-14-1-0383]; U. S. Department of Energy Office of Basic Energy Sciences, Division of Chemical Sciences [DEAC02-05CH11231]; US DOE Basic Energy Sciences [DE-SC0012198]; Arizona TRIF Photonics Fellowship

Decoding sequential vs non-sequential two-photon double ionization of helium using nuclear recoil

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An efficient basis set representation for calculating electrons in molecules

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Nuclear Dynamics in Resonant Electron Collisions with Small Polyatomic Molecules

, two-photon double ionization of helium is dominated by a sequential absorption process, producing characteristic behavior in the single and triple differential cross sections. We show that the signature of this process is visible in the nuclear recoil cross section, integrated over all energy sharings of the ejected electrons, even below the threshold for the sequential process. Since nuclear recoil momentum imaging does not require coincident photoelectron measurement, the predicted images present a viable target for future experiments with new short-pulse vacuum ultraviolet (vuv) and soft x-ray sources.