Vector correlations in dissociative photoionization of O2 in the 20–28 eV range. I. Electron-ion kinetic energy correlations

Abstract

Imaging and time resolved coincidence techniques are combined to determine ion-electron (VO+,Ve,P) velocity vector correlations in dissociative photoionization (DPI) of the O2 molecule induced by linearly polarized synchrotron radiation (P). The ion-electron kinetic energy correlations identify each DPI process by its reaction pathway, intermediate molecular state and dissociation limit. The 4π collection of ions and electrons provides their branching ratios. Up to 12 DPI processes are identified in the 20–28 eV range. Photoionization into the O2+(B 2∑g−) in the Franck–Condon (FC) region populating the [O+(4S)+O(3P)] limit is the dominant process. In the 22.3–24 eV region excitation of the O2*(3 2∏u,nsσg) Rydberg series, followed by dissociation and atomic autoionization to the [O+(2D)+O(3P)] limit reaches about 10% of the DPI flux. A new DPI process is identified in the same energy range, which populates the [O+(4S)+O(1D)] limit. At higher energies the relative weight of the four distinct processes which correspond to ionization into the O2+(3 2∏u) and O2+(c 4∑u−) states in the FC region and population of distinct excited limits is evaluated. The spatial analysis of the (VO+,Ve,P) vector correlation for selected processes will be discussed in a companion paper.

Valence and inner-valence shell dissociative photoionization of CO in the 26–33 eV range. II. Molecular-frame and recoil-frame photoelectron angular distributions

“…9,47,48 The molecular jet of CO was provided by the Spectropie d'Agrégats PhotoIonisés par Rayonnement Synchrotron (SAPHIRS) setup 49 which should have a rotational temperature of approximately 35 K based on a high-resolution pulsed field ionization photoelectron study 50 which used a very similar supersonic expansion. The linearly or circularly polarized synchrotron radiation light delivered by the undulator-based vacuum ultraviolet (VUV) beamline SU5 51, 52 at SuperACO (Orsay, France), operated in the two-bunch mode (period T = 120 ns, pulse width δt = 800 ps).…”

Circular dichroism in molecular frame photoemission

“…The coincident events for each studied DPI process were selected using the electron-ion kinetic energy correlation diagram as described in the earlier related papers [35,36,40,41], and illustrated in sect.6 for PI of NO at the 23. 65 and 25 eV photon excitation energies.…”

“…In smaller molecular systems, the MCSCI results can provide nearly quantitative agreement between the experiment and theory. This level of agreement has allowed for the study of dissociative lifetimes [39,40] and ion dynamics [41] through a comparison of measured and computed…”

“…This is known as the axial-recoil approximation [44]. However, when the lifetime of the dissociative state is a significant fraction of the rotational period of the molecule, the axial-recoil approximation is no longer valid and the effects of the rotation must be included in the calculation to allow for a direct comparison with experimental data [39,40]. In the case of the photoionization of NO considered here, one source of the discrepancy between theory and experiment may be long lifetimes of the ion states.…”

Ion–electron velocity vector correlations in dissociative photoionization of simple molecules using electrostatic lenses

“…Few setups of this type have been reported so far. 2,[5][6][7] In the velocity spectrometer developed previously in our group, 2,7 ions and electrons are extracted from the interaction region in opposite directions by a unique dc uniform electric field. Then they travel through a field free region before reaching a delay-line position sensitive detector.…”