Direct Experimental Evidence for Dissociative Photoionization of Oxygen Molecule via 2Σu– Ionic “Optical Dark” State

Ro-vibrational Distribution of NO+ Dissociated from NO2+ Ions in the a3B2 and b3A2 States: A Slow "Impulsive" Dissociation Example Revealed from Threshold Photoelectron-Photoion Coincidence Imaging

To clarify the contentions about dissociative photoionization mechanism of nitrogen dioxide via the a³B₂ and b³A₂ ionic states, a new threshold photoelectron-photoion coincidence (TPEPICO) velocity imaging has been conducted in the 12.8-14.0 eV energy range at the Hefei Light Source. The fine vibrational-resolved threshold photoelectron spectrum agrees well with the previous measurements. The ro-vibrational distributions of NO⁺, as the unique fragment ion in the dissociation of NO₂⁺ in specific vibronic levels of a³B₂ and b³A₂ states, are derived from the recorded TPEPICO velocity images. A "cold" vibrational (v⁺ = 0) and "hot" rotational population is observed at the a³B₂(0,3,0) and (0,4,0) vibronic levels, while the dissociation of NO₂⁺ in b³A₂(0,0,0) leads to the NO⁺ fragment with both hot vibrational and rotational populations. With the aid of the quantum chemical calculations at the time-dependent B3LYP level, minimum energy paths on the potential energy surfaces of the a³B₂ and b³A₂ states clarify their adiabatic dissociation mechanisms near the thresholds, and this study proposes reliable explanations for the observed internal energy distributions of fragment ions. Additionally, this study provides valuable insights into the application of the classical "impulsive" model on an overall slow dissociation process.

Cl-Loss dynamics in the dissociative photoionization of CF3Cl with threshold photoelectron–photoion coincidence imaging

Cl-loss dynamics in the dissociative photoionization of CF₃Cl was investigated in the photon energy range of 12.30–18.50 eV.

Advances in threshold photoelectron spectroscopy (TPES) and threshold photoelectron photoion coincidence (TPEPICO)

The history and evolution of molecular threshold photoelectron spectroscopy and threshold photoelectron photoion coincidence spectroscopy (TPEPICO) over the last fifty years are reviewed.

Vacuum upgrade and enhanced performances of the double imaging electron/ion coincidence end-station at the vacuum ultraviolet beamline DESIRS

We report here the recent upgrade of the SAPHIRS permanent photoionization end-station at the DESIRS vacuum ultraviolet beamline of synchrotron SOLEIL, whose performances have been enhanced by installing an additional double-skimmer differential chamber. The smaller molecular beam profile obtained at the interaction region has increased the mass resolution of the double imaging photoelectron photoion coincidence (i(2)PEPICO) spectrometer, DELICIOUS III, installed in the photoionization chamber of the SAPHIRS endstation, by a factor of two, to M/ΔM ∼ 1700 (FWHM). The electron kinetic energy resolution offered by the velocity map imaging (VMI) part of the spectrometer has been improved down to 2.8% (ΔE/E) as we show on the N2 photoionization case in the double skimmer configuration. As a representative example of the overall state-of-the-art i(2)PEPICO performances, experimental results of the dissociation of state-selected O2(+)(B(2)∑(g)(-), v(+) = 0-6) molecular ions performed at the fixed photon energy of hν = 21.1 eV are presented.