Satellite intensities in the K-shell photoionization of CO

Energy-Dependent Relative Cross Sections in Carbon 1s Photoionization: Separation of Direct Shake and Inelastic Scattering Effects in Single Molecules

We demonstrate that the possibility of monitoring relative photoionization cross sections over a large photon energy range allows us to study and disentangle shake processes and intramolecular inelastic scattering effects. In this gas-phase study, relative intensities of the carbon 1s photoelectron lines from chemically inequivalent carbon atoms in the same molecule have been measured as a function of the incident photon energy in the range of 300-6000 eV. We present relative cross sections for the chemically shifted carbon 1s lines in the photoelectron spectra of ethyl trifluoroacetate (the "ESCA" molecule). The results are compared with those of methyl trifluoroacetate and S-ethyl trifluorothioacetate as well as a series of chloro-substituted ethanes and 2-butyne. In the soft X-ray energy range, the cross sections show an extended X-ray absorption fine structure type of wiggles, as was previously observed for a series of chloroethanes. The oscillations are damped in the hard X-ray energy range, but deviations of cross-section ratios from stoichiometry persist, even at high energies. The current findings are supported by theoretical calculations based on a multiple scattering model. The use of soft and tender X-rays provides a more complete picture of the dominant processes accompanying photoionization. Such processes reduce the main photoelectron line intensities by 20-60%. Using both energy ranges enabled us to discern the process of intramolecular inelastic scattering of the outgoing electron, whose significance is otherwise difficult to assess for isolated molecules. This effect relates to the notion of the inelastic mean free path commonly used in photoemission studies of clusters and condensed matter.

An experimental and theoretical study of the C 1s ionization satellites in CH3I

The C 1s ionization spectrum of CH₃I has been studied both experimentally and theoretically. Synchrotron radiation has been employed to record polarization dependent photoelectron spectra at a photon energy of 614 eV. These spectra encompass the main-line due to the C 1s single-hole state and the peaks associated with the shake-up satellites. Vertical ionization energies and relative photoelectron intensities have been computed using the fourth-order algebraic-diagrammatic construction approximation scheme for the one-particle Green's function and the 6-311++G^** basis set. The theoretical spectrum derived from these calculations agrees qualitatively with the experimental results, thereby allowing the principal spectral features to be assigned. According to our calculations, two ²A₁ shake-up states of the C 1s^-1 σ_CI → σ_CI ^* type with singlet and triplet intermediate coupling of the electron spins (S' = 0, 1) play an important role in the spectrum and contribute significantly to the overall intensity. Both of these states are expected to have dissociative diabatic potential energy surfaces with respect to the C-I separation. Whereas the upper of these states perturbs the manifold of Rydberg states, the lower state forms a band which is characterized by a strongly increased width. Our results indicate that the lowest shake-up peak with significant spectral intensity is due to the pair (S' = 0, 1) of ²E (C 1s^-1 I 5p → σ_CI ^*) states. We predict that these ²E states acquire photoelectron intensity due to spin-orbit interaction. Such interactions play an important role here due to the involvement of the I 5p orbitals.

Interchannel coupling effects in the valence photoionization of SF6

The complex Kohn and polyatomic Schwinger variational techniques have been employed to illustrate the interchannel coupling correlation effects in the valence photoionization dynamics of SF6. Partial photoionization cross sections and asymmetry parameters of six valence subshells (1t1g, 5t1u, 1t2u, 3eg, 1t2g, 4t1u) are discussed in the framework of several theoretical and experimental studies. The complex Kohn results are in rather good agreement with experimental results, indicative of the fact that the interchannel coupling effects alter the photoionization dynamics significantly. We find that the dominant effect of interchannel coupling is to reduce the magnitude of shape resonant cross sections near the threshold and to induce resonant features in other channels to which resonances are coupled. The long-standing issue concerning ordering of the valence orbitals is addressed and confirmed 4t1u (6)1t2g (6)3eg (4)(5t1u (6)+1t2u (6)) 1t1g (6) as the most likely ordering.

Near-edge x-ray absorption fine structures revealed in core ionization photoelectron spectroscopy

Simultaneous core ionization and core excitation have been observed in the C(2)H(2n) (n=1, 2, 3) molecular series using synchrotron radiation and a magnetic bottle time-of-flight electron spectrometer. Rich satellite patterns corresponding to (K(-2)V) core excited states of the K(-1) molecular ions have been identified by detecting in coincidence the photoelectron with the two Auger electrons resulting from the double core hole relaxation. A theoretical model is proposed providing absolute photoionization cross sections and revealing clear signatures of direct (monopolar) and conjugate (dipolar near-edge x-ray absorption fine structure) shakeup lines of comparable magnitude.

Internal inelastic scattering satellite probed by molecular-frame photoelectron angular distributions from CO2

The molecular-frame photoelectron angular distribution (MFPAD) of the satellite accompanying the C 1s photoline of the CO2 molecule has been measured at the C 1s(2sigmag)-->4sigmau* shape resonance, using electron-ion multicoincidence momentum spectroscopy. The observed MFPAD indicates that the conjugate satellite is excited by internal inelastic scattering. In this scenario, a photoelectron is ejected from the C 1s(2sigmag) orbital along the molecular axis and collides with an O lone-pair electron in the highest occupied molecular orbital 1pig. Then one of the colliding electrons is trapped to the lowest unoccupied molecular orbital 2piu*, while the other is emitted as a satellite photoelectron of sigmag symmetry, losing the information of the original photoelectron emission direction and parity.

Symmetry-dependent vibrational excitation in N 1s photoionization of N2: Experiment and theory

We have measured the vibrational structures of the N 1s photoelectron mainline and satellites of the gaseous N2 molecule with the resolution better than 75 meV. The gerade and ungerade symmetries of the core-ionized (mainline) states are resolved energetically, and symmetry-dependent angular distributions for the satellite emission allow us to resolve the Sigma and Pi symmetries of the shake-up (satellite) states. Symmetry-adapted cluster-expansion configuration-interaction calculations of the potential energy curves for the mainline and satellite states along with a Franck-Condon analysis well reproduce the observed vibrational excitation of the bands, illustrating that the theoretical calculations well predict the symmetry-dependent geometry relaxation effects. The energies of both mainline states and satellite states, as well as the splitting between the mainline gerade and ungerade states, are also well reproduced by the calculation: the splitting between the satellite gerade and ungerade states is calculated to be smaller than the experimental detection limit.