Photodissociation of gas-phase I3−: Comprehensive understanding of nonadiabatic dissociation dynamics

Probing the molecular structure of aqueous triiodide via X-ray photoelectron spectroscopy and correlated electron phenomena

Liquid-microjet-based X-ray photoelectron spectroscopy was applied to aqueous triiodide solutions, I₃^-_(aq.), to investigate the anion's valence- and core-level electronic structure, ionization dynamics, associated electron-correlation effects, and nuclear geometric structure. The roles of multi-active-electron (shake-up) ionization processes - with noted sensitivity to the solute geometric structure - were investigated through I₃^-_(aq.) solution valence, I 4d, and I 3d core-level measurements. The experimental spectra were interpreted with the aid of simulated photoelectron spectra, built upon multi-reference ab initio electronic structure calculations associated with different I₃^-_(aq.) molecular geometries. A comparison of the single-to-multi-active-electron ionization signal ratios extracted from the experimental and theoretical core-level photoemission spectra suggests that the ground state of the solute adopts a near-linear average geometry in aqueous solutions. This contrasts with the interpretation of time-resolved X-ray solution scattering studies, but is found to be fully consistent with the rest of the solution-phase I₃^-_(aq.) literature. Comparing the results of low- and high-photon-energy photoemission measurements, we further suggest that the aqueous anion adopts a more asymmetric geometry at the aqueous-solution-gas interface than in the aqueous bulk.

Self-assembling of the neutral intermediate with chemically bound argon in photoexcited van der Waals complex Ar-I2

Photodissociation of the van der Waals complex Ar-I₂ after excitation into the Rydberg states of I₂ has been investigated with velocity map imaging of photofragments. Formation of the translationally hot ions of argon Ar⁺ with three modes in kinetic energy distribution has been revealed. The measured dependence of the kinetic energy of Ar⁺ on the pumping photon energy indicates the appearance of Ar⁺ from three channels of the photodissociation of the linear intermediate Ar⁺-I-I^- containing chemically bound argon. These channels are (1) dissociation into Ar⁺+ I₂ ^-; (2) three-body dissociation into (Ar⁺)* + I* + I^-, with (Ar⁺)* and I* being the ²P_1/2 states of the species; and (3) two-body electron photodetachment, giving rise to Ar⁺ + I₂ + e. Three indicated channels are similar to those established for the photodissociation of trihalide anions. This similarity confirms the conclusion on the formation of the Ar⁺-I-I^- intermediate, which is isoelectronic to the trihalide anion Cl-I-I^-. The mechanism of the Ar⁺-I-I^- formation involves two-photon excitation of the complex Ar-I₂ into the Rydberg state of I₂ converted into the ion-pair state and further electron transfer from Ar to I⁺ of the ion-pair state. The self-assembling of the structure making the formation of the Ar⁺-I-I^- intermediate energetically accessible is confirmed by modeling the dynamics in the excited linear complex Ar-I₂. Photoexcitation of the van der Waals complexes of noble gases with halogens into the ion-pair states of halogen is supposed to be a promising approach for generating the new chemical compounds of noble gas atoms.

Spectroscopic characterisation of radical polyinterhalogen molecules

Spectroscopic characterisations of the radical polyinterhalogen molecules IF2 and I2F are reported using anion photoelectron spectroscopy. The corresponding parent anions, IF2- and I2F-, are common products formed in hard Ar-CF3I plasmas and are relevant in the semiconductor manufacture industry. The I2F- species, which is present as the [I-I-F]- isomer, is a "non-classical" polyinterhalogen.

Photoelectron-photofragment coincidence studies of I3- using an electrospray ionization source and a linear accelerator

Photoelectron-photofragment coincidence (PPC) spectroscopy is used to examine the dissociative photodetachment (DPD) of I3-. The high beam energy PPC spectrometer for complex anions couples an electrospray ionization source, a hexapole accumulation ion trap and a linear accelerator to produce fast beams of I3- (M = 381 amu) anions, the heaviest system studied to date. Following photodetachment, the photoelectron and up to three photofragments are recorded in coincidence yielding a kinematically complete picture of the DPD dynamics at beam energies of 11 keV and 21 keV. Photodetachment leads to the production of stable I3, two-body DPD, as well as evidence for two- and three-body photodissociation. DPD is found to occur predominantly via the first excited A state, with some contributions from highly excited vibrational levels in the neutral ground state. With the ions thermalized to 298 K in the hexapole trap, there are significant contributions from vibrational hot bands. Three-body photodissociation at 4.66 eV is found to occur preferentially via a charge-symmetric process to form I + I- + I. In the future this method will be applied to other polyatomic systems with a large molecular mass, including multiply charged anions and complex clusters, in concert with a cryogenically cooled hexapole trap to reduce thermal effects.

Towards understanding triiodide photochemistry in the solid state by femtosecond electron diffraction

The photochemistry of the triiodide anion has been investigated by femtosecond electron diffraction. The time-resolved signal indicates the presence of reaction products and large-amplitude coherent motion produced by participating species. To reconstruct the atomic detail of the reaction and identify the major contributors to the detected signal, we outline the approach for atomic-level reconstruction.

Identification of photofragmentation patterns in trihalide anions by global analysis of vibrational wavepacket dynamics in broadband transient absorption data

Photodissociation pathways of a trihalide series are systematically investigated by globally fitting vibrational wavepacket signals in broadband transient absorption spectra.

Excited-state wavepacket and potential reconstruction by coherent anti-Stokes Raman scattering

We propose a methodology for reconstructing polyatomic excited-state molecular wavepackets and potential energy surfaces by multiple pulse optical spectroscopy.

Unprecedented transformation of [I−·I3−] to [I42−] polyiodides in the solid state: structures, phase transitions and characterization of dipyrazolium iodide triiodide

Dipyrazolium iodide triiodide, [C₃N₂H₅⁺]₂[I⁻·I₃⁻], has been synthesized and studied by means of X-ray diffraction, differential scanning calorimetry, dielectric measurements, and UV-Vis spectroscopy.