Deep-core photoionization of krypton atoms below and above the 1s ionization threshold

Electronic relaxation of atomic Kr below and above the 1s ionization threshold is investigated experimentally using hard x-ray photoelectron spectroscopy. The experimental results are interpreted with the aid of relativistic Dirac-Fock calculations. The 1s orbital core-hole lifetime is extracted and the satellite's structures accompanying the photoelectron main line are assigned. Auger spectra recorded below and above the K edge are also investigated. In particular, the Auger cascade originating from vacancies of different origin in the L shell is analyzed in great detail. Competition between radiative KL versus nonradiative KLL Auger emission is emphasized

Deep core photoelectron spectroscopic studies of atoms and molecules using hard x-ray

Abstract In this thesis the electronic structure and dynamics of iodine, krypton and bromine atoms in isolated and molecular forms are investigated through K-shell photoexcitation and subsequent Auger decay. The experimental studies are carried out using hard x-ray photoelectron spectroscopic techniques and the theoretical work by applying relativistic ab initio quantum mechanical models. The reported photoelectron spectra from iodine compounds CH3I and CF3I have the highest binding energy, 33.2 keV, recorded from any molecule in the gas phase up to date. From the spectra it is shown that chemical shifts are observable even at such deep core orbitals. From krypton a detailed analysis of Auger decay and Fluorescence cascade following K and L-shell ionization up to quadruple ionized states is presented. The work concerning bromine provides an analysis of photoionization, excitation, lifetime, Auger decay and nuclear dynamics around the K-edge of HBr molecule

Experimental and theoretical study of the Kr L-shell Auger decay

The LMM Auger spectra of krypton are measured using the photon energies hν=1709 eV, 1792 eV, 1950 eV, and 13 keV. This approach allows separating the contributions from the various core holes L1, L2, and L3. Previously unobserved transitions are presented. Complementary theoretical work is performed allowing the assignment of the spectral features. The L2,3Y−MMY (Y=M4,5,N1,2,3) Auger transitions of Kr2+ formed via Coster-Kronig Auger decay of the core holes L1 and L2 are also investigated. These spectra comprise about 4000 and 13 000 transitions, respectively, so that only general statements on the assignment, such as the configurations involved in the transitions, can be given

Experimental and theoretical study of the Kr L-shell Auger decay

Abstract The LMM Auger spectra of krypton are measured using the photon energies hν = 1709 eV, 1792 eV, 1950 eV, and 13 keV. This approach allows separating the contributions from the various core holes L₁, L₂, and L₃. Previously unobserved transitions are presented. Complementary theoretical work is performed allowing the assignment of the spectral features. The L2,3Y -MMY (Y = M4,5, N1,2,3 ) Auger transitions of Kr2+ formed via Coster-Kronig Auger decay of the core holes L₁ and L₂ are also investigated. These spectra comprise about 4000 and 13 000 transitions, respectively, so that only general statements on the assignment, such as the configurations involved in the transitions, can be given

Deep-core photoionization of krypton atoms below and above the 1s ionization threshold

Abstract Electronic relaxation of atomic Kr below and above the 1s ionization threshold is investigated experimentally using hard x-ray photoelectron spectroscopy. The experimental results are interpreted with the aid of relativistic Dirac-Fock calculations. The 1s orbital core-hole lifetime is extracted and the satellite’s structures accompanying the photoelectron main line are assigned. Auger spectra recorded below and above the K edge are also investigated. In particular, the Auger cascade originating from vacancies of different origin in the L shell is analyzed in great detail. Competition between radiative KL versus nonradiative KLL Auger emission is emphasized

Electron–ion coincidence spectroscopy of a large organic molecule:photofragmentation of avobenzone after valence and core ionisation

Abstract The Avobenzone (AVOB) molecule is very photoactive and undergoes irreversible degradation upon irradiation. We studied its valence and core-level (C1s and O1s) photoionisation and subsequent photofragmentation with photoelectron spectroscopy and photoelectron–photoion–photoion coincidence (PEPIPICO) spectroscopy. AVOB is one of the largest molecules studied with this technique. The results show that the AVOB molecule dissociates into an extensive range of fragments by different pathways with little element or site-selectivity. The coincident maps were used to determine selected fragment separation sequences by analysing the slopes of patterns from ion pairs after the core ionisation. Charge delocalisation over the benzene rings and their relative stability favor fragmentation by cleavage of the bridge between them

Deep core photoionization of iodine in CH₃I and CF₃I molecules:how deep down does the chemical shift reach?

Abstract Hard X-ray electron spectroscopic study of iodine 1s and 2s photoionization of iodomethane (CH₃I) and trifluoroiodomethane (CF₃I) molecules is presented. The experiment was carried out at the SPring-8 synchrotron radiation facility in Japan. The results are analyzed with the aid of relativistic molecular and atomic calculations. It is shown that charge redistribution within the molecule is experimentally observable even for very deep levels and is a function of the number of electron vacancies. We also show that the analysis of Auger spectra subsequent to hard X-ray photoionization can be used to provide insight into charge distribution in molecules and highlight the necessity of quantum electrodynamics corrections in the prediction of core shell binding energies in molecules that contain heavy atoms

Forming bonds while breaking old ones:isomer-dependent formation of H₃O⁺ from aminobenzoic acid during X-ray-induced fragmentation

Abstract Intramolecular hydrogen transfer, a reaction where donor and acceptor sites of a hydrogen atom are part of the same molecule, is a ubiquitous reaction in biochemistry and organic synthesis. In this work, we report hydronium ion (H₃O⁺) production from aminobenzoic acid (ABA) after core-level ionization with soft X-ray synchrotron radiation. The formation of H₃O⁺ during the fragmentation requires that at least two hydrogen atoms migrate to one of the oxygen atoms within the molecule. The comparison of two structural isomers, ortho- and meta-ABA, revealed that the production of H₃O⁺ depends strongly on the structure of the molecule, the ortho-isomer being much more prone to produce H₃O⁺. The isomer-dependency suggests that the amine group acts as a donor in the hydrogen transfer process. In the case of ortho-ABA, detailed H₃O⁺ production pathways were investigated using photoelectron-photoion-photoion coincidence (PEPIPICO) spectroscopy. It was found that H₃O⁺ can result from a direct two-body dissociation but also from sequential fragmentation processes

The effect of relative humidity on CaCl₂ nanoparticles studied by soft X-ray absorption spectroscopy

Abstract Ca- and Cl-containing nanoparticles are common in atmosphere, originating for example from desert dust and sea water. The properties and effects on atmospheric processes of these aerosol particles depend on the relative humidity (RH) as they are often both hygroscopic and deliquescent. We present here a study of surface structure of free-flying CaCl₂ nanoparticles (CaCl₂-NPs) in the 100 nm size regime prepared at different humidity levels (RH: 11–85%). We also created mixed nanoparticles by aerosolizing a solution of CaCl₂ and phenylalanine (Phe), which is a hydrophobic amino acid present in atmosphere. Information of hydration state of CaCl₂-NPs and production of mixed CaCl₂ + Phe nanoparticles was obtained using soft X-ray absorption spectroscopy (XAS) at Ca 2p, Cl 2p, C 1s, and O 1s edges. We also report Ca 2p and Cl 2p X-ray absorption spectra of an aqueous CaCl₂ solution. The O 1s X-ray absorption spectra measured from hydrated CaCl2-NPs resemble liquid-like water spectrum, which is heavily influenced by the presence of ions. Core level spectra of Ca²⁺ and Cl⁻ ions do not show a clear dependence of % RH, indicating that the first coordination shell remains similar in all measured hydrated CaCl₂-NPs, but they differ from aqueous solution and solid CaCl₂

Electron spectroscopy and dynamics of HBr around the Br 1s⁻¹ threshold

Abstract A comprehensive electron spectroscopic study combined with partial electron yield measurements around the Br 1s ionization threshold of HBr at ≅13.482 keV is reported. In detail, the Br 1s⁻¹ X-ray absorption spectrum, the 1s⁻¹ photoelectron spectrum as well as the normal and resonant KLL Auger spectra are presented. Moreover, the L-shell Auger spectra measured with photon energies below and above the Br 1s⁻¹ ionization energy as well as on top of the Br 1s⁻¹σ* resonance are shown. The latter two Auger spectra represent the second step of the decay cascade subsequent to producing a Br 1s⁻¹ core hole. The measurements provide information on the electron and nuclear dynamics of deep core-excited states of HBr on the femtosecond timescale. From the different spectra the lifetime broadening of the Br 1s⁻¹ single core-hole state as well as of the Br(2s⁻²,2s⁻¹2p⁻¹,2p⁻²) double core-hole states are extracted and discussed. The slope of the strongly dissociative HBr 2p⁻²σ* potential energy curve is found to be about −13.60 eV Å⁻¹. The interpretation of the experimental data, and in particular the assignment of the spectral features in the KLL and L-shell Auger spectra, is supported by relativistic calculations for HBr molecule and atomic Br