Dissociative Multiple Ionization following Valence, Br(3d), and Si(2p) Inner Shell Photoexcitation of SiBr₄ in the Range of 30−133 eV

Abstract

The photoionization of SiBr4 in the valence shell, and the Br(3d) and Si(2p) inner shell excitation/ionization regions, has been studied by using a time-of-flight mass spectrometer and synchrotron radiation over the range 30−133 eV. The photoionization efficiency curve of SiBr4 has been recorded as a function of the incident photon energy. Dissociation processes of SiBr4 have also been investigated by photoelectron−photoion coincidence and photoion-photoion coincidence (PIPICO) techniques. Various monocations of Br n + (n = 1, 2) and SiBr n + (n = 0−4) are detected along with dications of Br2+ and SiBr n 2+ (n = 0, 1, 3) in the energy range. Various dissociation patterns are proposed based on the measurements of the ion time-of-flight differences in the PIPICO mode. The dominant dissociation pattern is found to be Si+−Br+ and SiBr+−Br+ in the whole energy examined. In the Br(3d) excitation region, however, a fragmentation leading to ion pair such as SiBr3 +−Br+ also plays an important role in the dissociation of the core-excited SiBr4. With the help of ab initio Hartree−Fock and previous CI calculations, we estimate the term values and symmetries of the discrete core-excited states. This study of the specific excitation and dissociation of molecules provides information on energy dissipation processes of the core-excited states.

Pathway Studies in Si(2p) Inner-Shell Processes of H2Si(CH3)2 by Mass Spectrometry and the Photoion−Photoion Coincidence Method in the Range 24−133 eV

“…The discrepancy between theory and experiment may reflect that the HF/6-311++G(2df,p) calculation may greatly underestimate the term values corresponding to the transition, although the Si(2p) electrons cannot efficiently screen the nuclear charge owing to the extensive d character. It is shown in previous literature that the term values determined by the configuration interaction calculation match better with experiment than do those determined by the HF calculation. , However, it should be pointed out that calculated term values suppose two separate calculations, one of the initial state and one of the final state, and therefore our simple calculation of virtual orbital energies by using the EICVOM theory could only help to assign the discrete excitation states.

2 Total photoion−photoion yield curve of H 2 Si(CH 3 ) 2 in the range of 65−133 eV.

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“…Hence, the transitions below 106.51 eV are attributed to the discrete excitation of the Si(2p) core electron to the unoccupied antibonding and Rydberg orbitals. Previous studies show that the excitation of Si(2p) core electron to the first antibonding orbital occurs when the incident photon energy reaches ≈ 103 eV, the energy being more or less shifted with different ligands. − ,− Chemical shifts of photoelectron and Auger lines are linearly dependent on the average differences in Pauling's electronegativities to the nearest neighbors, Δχ P .…”

“…It is shown in previous literature that the term values determined by the configuration interaction calculation match better with experiment than do those determined by the HF calculation. 2,7 However, it should be pointed out that calculated term values suppose two separate calculations, one of the initial state and one of the final state, and therefore our simple calculation of virtual orbital energies by using the EICVOM theory could only help to assign the discrete excitation states.…”

“…In recent years, extensive studies have been made of the energetics, spectroscopy, and dynamics of the core-hole excited states involving Si(1s), − Si(2s), and Si(2p) − cores by various methods such as X-ray photoabsorption spectroscopy, − discrete variational (DV) X α method, multiple-scattering (MS) X α method, and electron energy loss spectroscopy . The interpretation of the photoionization mass spectra of molecules is of much importance to infer the electronic and charge states of the parent ions.…”

The Role of Spin–Orbit Coupling in the Double-Ionization Photoelectron Spectra of XCN2+ (X = Cl, Br, and I)

“…In recent years, the coincidence techniques have been applied to explore the excited states of several systems. Using the PEPICO method, ionization processes of rare gases, CF 4 , CH 3 , N 2 , CF 3 Br, SiCl 4 , C 4 F 8 , and even some clusters have been recently studied. − Several small molecules, for example, H 2 , Br 2 , CO 2 , OCS, have been studied by PIPICO technique, − whereas photoionization of CS 2 , NO 2 , SO 2 , and CH 3 I has been successfully investigated by PEPIPICO method …”