Sulfur 1s core-level photoionization of SF6

Cation and Anion Formation in F 1s-Excited SF6-Clusters

Cation and anion formation from molecular SF6 and SF6 clusters is reported in the F 1s-excitation regime (680–720 eV) using tunable synchrotron radiation. Stable products are identified by mass spectrometry, while the tunablility of the soft X-rays source is used to determine mechanistic details on the formation of the detected charged products. Characteristic differences are observed between product formation from the isolated molecule as well as from clusters for both, cations and anions. Specifically, dication formation, such as SF2 2+, is only observed for molecular precursors, which are formed with high efficiency at the F 1s → t2g-transition. SF6 − is efficiently formed from clusters upon F 1s → t1u-transition. Mechanistic details on the formation of stable products are discussed.

Positive and negative ion formation in deep-core excited molecules: S 1s excitation in dimethyl sulfoxide

The photo-fragmentation of the dimethyl sulfoxide (DMSO) molecule was studied using synchrotron radiation and a magnetic mass spectrometer. The total cationic yield spectrum was recorded in the photon energy region around the sulfur K edge. The sulfur composition of the highest occupied molecular orbital's and lowest unoccupied molecular orbital's in the DMSO molecule has been obtained using both ab initio and density functional theory methods. Partial cation and anion-yield measurements were obtained in the same energy range. An intense resonance is observed at 2475.4 eV. Sulfur atomic ions present a richer structure around this resonant feature, as compared to other fragment ions. The yield curves are similar for most of the other ionic species, which we interpret as due to cascade Auger processes leading to multiply charged species which then undergo Coulomb explosion. The anions S(-), C(-), and O(-) are observed for the first time in deep-core-level excitation of DMSO.

Time dependent density functional study of the photoionization dynamics of SF6

The B-spline linear combination of atomic orbitals method has been employed to study the valence and core photoionization dynamics of SF6. The cross section and asymmetry parameter profiles calculated at the time dependent density functional theory level have been found to be in fairly nice agreement with the experimental data, with the quality of the exchange-correlation statistical average of orbital potential results superior to the Van Leeuwen-Baerends 94 (LB94) ones [Phys. Rev. A 49, 2421 (1994)]. The role of response effects has been identified by a comparison of the time dependent density functional theory results with the Kohn-Sham ones interchannel coupling effects and autoionization resonances play an important role at low kinetic energies. Prominent shape resonances features have been analyzed in terms of "dipole prepared" continuum orbitals and interpreted as due to a large angular momentum centrifugal barrier as well as anisotropic (nonspherical) molecular effective potential. Finally, the method has been proven numerically stable, robust, and efficient, thanks to a noniterative implementation of the time dependent density functional theory equations and suitability of the multicentric B-spline basis set to describe continuum states from outer valence to deep core states.