Alfred S. Schlachter

Detailed study of pyridine at the C 1s and N 1s ionization thresholds: The influence of the vibrational fine structure

High resolution, vibrationally resolved, near-edge x-ray absorption fine structure (NEXAFS) spectra at the C 1s and N 1s ionization thresholds of pyridine and deuterated d5-pyridine in the gas phase have been recorded. The high resolution of 65 meV (150 meV) at the C s (N 1s) ionization thresholds reveals vibrational structures in the spectra. Detailed ab initio and density functional theory (DFT) calculations were performed to interpret the experimental spectra and to assign the observed peaks. In particular we focused on the previously unexplained intensity ratio for the two components of the C 1s→1π* transition. For this transition the vibrational structure is included through a linear coupling model in the DFT calculations and leads to the experimentally observed ∼2:3 intensity ratio between the two π* components in the C 1s spectrum rather than the ∼3:2 ratio obtained without vibrational effects. After inclusion of relaxation effects in the excited states, in addition to the vibrational effects, both...

Spectroscopic analysis of small organic molecules: A comprehensive near-edge x-ray-absorption fine-structure study of C6-ring-containing molecules

We report high-resolution C 1s near-edge x-ray-absorption fine-structure (NEXAFS) spectra of the C6-ring-containing molecules benzene (C6H6), 1,3- and 1,4-cyclohexadiene (C6H8), cyclohexene (C6H10), cyclohexane (C6H12), styrene (C8H8), and ethylbenzene (C8H10) which allow us to examine the gradual development of delocalization of the corresponding pi electron systems. Due to the high experimental resolution, vibrational progressions can be partly resolved in the spectra. The experimental spectra are compared with theoretical NEXAFS spectra obtained from density-functional theory calculations where electronic final-state relaxation is accounted for. The comparison yields very good agreement between theoretical spectra and experimental results. In all cases, the spectra can be described by excitations to pi*- and sigma*-type final-state orbitals with valence character, while final-state orbitals of Rydberg character make only minor contributions. The lowest C 1s-->1pi* excitation energy is found to agree in the (experimental and theoretical) spectra of all molecules except for 1,3-cyclohexadiene (C6H8) where an energy smaller by about 0.6 eV is obtained. The theoretical analysis can explain this result by different binding properties of this molecule compared to the others.

Anion and cation formation following core-level photoexcitation of CO2

Mass-resolved anion and cation partial-yield spectra following photoexcitation of CO2 have been recorded in the vicinity of the C 1s and O 1s thresholds. Anion production was found to be site specific: a weak production of O− was observed on the π* resonance near the C K edge, whereas both C− and O− fragments were observed near the O K edge. Due to suppression of the shape resonances that dominate the cross section above the core thresholds, the anion-partial-yield spectra at the O K edge reveal several previously unobserved electronic states. In addition, several cations such as CO2+ and O2+ were observed for the first time.

K-shell photoionization of ground-state Li-like carbon ions [C3+]: experiment, theory and comparison with time-reversed photorecombination

Absolute cross sections for the K-shell photoionization of ground-state Li-like carbon [C3+(1s22s 2S)] ions were measured by employing the ion?photon merged-beams technique at the Advanced Light Source. The energy ranges 299.8?300.15?eV, 303.29?303.58?eV and 335.61?337.57?eV of the [1s(2s2p)3P]2P, [1s(2s2p)1P]2P and [(1s2s)3S 3p]2P resonances, respectively, were investigated using resolving powers of up to 6000. The autoionization linewidth of the [1s(2s2p)1P]2P resonance was measured to be 27 ? 5?meV and compares favourably with a theoretical result of 26?meV obtained from the intermediate coupling R-matrix method. The present photoionization cross section results are compared with the outcome from photorecombination measurements by employing the principle of detailed balance.

Fragmentation processes following core excitation in acetylene and ethylene by partial ion yield spectroscopy

Partial ion yield spectroscopy provides a very detailed picture of fragmentation processes following core excitation in isolated molecules. We exploit this potential in the analysis of decay processes following C1s→π and C1s→Rydberg excitations in ethylene and acetylene. We show that the relative intensity of spectral features related to the excitation to empty molecular orbitals or to Rydberg states is a function of the time variation of the fragmentation process. Namely, we see an intensity increase in the Rydberg states compared to the molecular orbitals as the fragmentation process becomes more extensive, a result attributable to the diffuse nature of the Rydberg virtual orbitals, which makes spectator decay more likely than participator decay. Therefore, the number of dissociative final states that can be reached from Rydberg excitation is higher than for excitation to empty molecular orbitals. In acetylene, we obtain the first direct evidence of the presence of a σ* excitation embedded in the Rydber...

Valence-shell photoionization of chlorinelike Ar+ ions

Absolute cross-section measurements for valence-shell photoionization of Ar

ABSOLUTE PHOTOIONIZATION CROSS SECTION MEASUREMENTS OF O ii IONS FROM 29.7 TO 46.2 eV

{}^{+}

Photoionization of C2+ ions: time-reversed recombination of C3+ with electrons

ions are reported for photon energies ranging from 27.4 to 60.0 eV. The data, taken by merging beams of ions and synchrotron radiation at a photon energy resolution of 10 meV, indicate that the primary ion beam was a statistically weighted mixture of the

Lifetime of a K-shell vacancy in atomic carbon created by 1s → 2p photoexcitation of C+

{}^{2}{P}_{3/2}^{o}

K-shell photoionization of Be-like boron (B+) ions: experiment and theory

ground state and the