Chemical Insights from High-Resolution X-ray Photoelectron Spectroscopy and ab Initio Theory: Propyne, Trifluoropropyne, and Ethynylsulfur Pentafluoride

High-resolution carbon 1s photoelectron spectroscopy of propyne (HC=CH3) shows a spectrum in which the contributions from the three chemically inequivalent carbons are clearly resolved and marked by distinct vibrational structure. This structure is well accounted for by ab initio theory. For 3,3,3-trifluoropropyne (HC=CF3) and ethynylsulfur pentafluoride (HC=SF5), the ethynyl carbons show only a broad structure and have energies that differ only slightly from one another. The core-ionization energies can be qualitatively understood in terms of conventional resonance structures; the vibrational broadening for the fluorinated compounds can be understood in terms of the effects of the electronegative fluorines on the charge distribution. Combining the experimental results with gas-phase acidities and with ab initio calculations provides insights into the effects of initial-state charge distribution and final-state charge redistribution on ionization energies and acidities. In particular, these considerations make it possible to understand the apparent paradox that SF5 and CF3 have much larger electronegativity effects on acidity than they have on carbon 1s ionization energies

Vibrationally resolved photoelectron spectra of the carbon 1s and nitrogen 1s shells in hydrogen cyanide

Vibrational structures of the C1s and N1s photoelectron spectra of gas-phase HCN have been investigated using monochromated third-generation synchrotron radiation. Both spectra exhibit resolved fine structure associated with several vibrationally excited states. In the C1s spectrum a single vibrational progression is observed, while the N1s spectrum is more complex. High-level ab initio calculations were performed to simulate the spectra and the agreement with the experimental results is good. Based on the calculations, the C1s ionisation is found to induce vibrations solely in the C≡N stretching mode with an energy of 280 meV, while the N1s ionisation generates vibrations also in the C-H stretching mode with an energy of about 387 meV, as well as combinations of these two modes

Laboratory-frame electron angular distributions: Probing the chemical environment through intramolecular electron scattering

Carbon 1s photoelectron asymmetry parameters β for the chlorinated and the methyl carbon atom of CH₃CH₂Cl, CH₃CHCl₂, and CH₃CCl₃ have been measured using synchrotron radiation in the 340-600 eV energy range. We provide experimental evidence that the intramolecular scattering strongly affects beta values, even far from the ionization threshold. The results are in agreement with B-spline density functional theory calculations, making it possible to single out the behavior of the various continuum partial waves. We conclude that the intramolecular scattering makes electron angular distributions sensitive to the chemical environment, even in isolated gas phase molecules.Keywords: Molecular orbital methods, Edge, Gaussian basis sets, Absorption fine structure, Row atoms, Photoemission, Wave functions, Potentials, 1s photoelectron spectroscopy, Photoionizatio

Nonstoichiometric Intensities in Core Photoelectron Spectroscopy

X-ray photoemission spectroscopy is used in a great variety of research fields; one observable is the sample's stoichiometry. The stoichiometry can be deduced based on the expectation that the ionization cross sections for innershell orbitals are independent of the molecular composition. Here we used chlorine-substituted ethanes in the gas phase to investigate the apparent carbon stoichiometry. We observe a nonstoichiometric ratio for a wide range of photon energies, the ratio exhibits x-ray-absorption fine structure spectroscopy (EXAFS)-like oscillations and hundreds of eV above the C1s ionization approaches a value far from 1. These effects can be accounted for by considering the scattering of the outgoing photoelectron, which we model by multiple-scattering EXAFS calculations, and by considering the effects of losses due to monopole shakeup and shakeoff and to intramolecular inelastic scattering processes.This is the publisher’s final pdf. The published article is copyrighted by American Physical Society and can be found at: http://prl.aps.org/Keywords: Absorption fine structure, Photoemissio