Cascade Auger decays following Si KL23L23 Auger transitions in SiF4

Abstract

Cascade Si LVV Auger decays following KL(23)L(23) Auger transitions have been measured in SiF(4) molecule using an electron spectrometer combined with monochromatized undulator radiation. Molecular cascade processes from the two 2p holes states largely generate wide band structures in the spectra due to sequential electron emission leading to multiple valence holes. However, a peak with high yield is observed for the first time at about 103 eV, an energy being considerably higher than the energies of the normal LVV Auger electron, in the instance of the resonant excitation of Si 1s electron into the vacant molecular orbital. This peak is presumed to originate from the participator decay from the state with two 2p holes and one excited electron into the state with one 2p hole and one valence hole. A similar peak with less intensity is detected in the photoexcitation of the 1s electron into a Rydberg orbital. After the normal KL(23)L(23) Auger transition, the resultant cascade spectrum shows several peaks, e.g., 61 eV, 76 eV, and 82 eV. The former two peaks are assigned to the Auger transitions of Si atoms produced through molecular ion dissociation after cascade decays, and the latter is probably ascribed to the second step Auger decay into states having a 2p hole together with two valence holes.

Site-Specific Electron-Relaxation Caused by Si:2p Core-Level Photoionization: Comparison between F3SiCH2CH2Si(CH3)3 and Cl3SiCH2CH2Si(CH3)3 Vapors by Means of Photoelectron Auger Electron Coincidence Spectroscopy

“…In Figures and , the Si­[Me]:L 23 VV AES of FSMSE and CSMSE are close to each other, and similar to that of Si­(CH 3 ) 4 vapor. , However, the Si­[X]:L 23 VV AES of FSMSE and CSMSE are totally different from each other. Furthermore, those are similar to the Si:L 23 VV AES of SiF 4 and SiCl 4 vapors, ,,, as mentioned in sections and . These observations of the Si­[XR]:L 23 VV AES of FSMSE and CSMSE (XR = F, Cl, or Me) would also show that the site specificity is maintained up to the Auger electron emission even in CSMSE.…”

“…The summation of the computational Si­[X]:L 23 VV and Si­[Me]:L 23 VV Auger electron spectra (AES) in each molecule is given in Figures a and a. For comparison, Figures and also represent Si:L 23 VV AES of Si­(CH 3 ) 4 , SiF 4 , and SiCl 4 vapors obtained previously. − The computational spectra of FSMSE and CSMSE given in Figures and are fairly consistent with the experimental spectra. The spectra of FSMSE vapor (Figure a–c) are similar to those obtained for condensed F 3 SiCD 2 CH 2 Si­(CH 3 ) 3 …”

“…In Figure c, FSMSE shows a Si­[F]:L 23 VV Auger peak at 73.4 eV, which comes from hole creation in higher-lying Si­[F]–CH 2 (bridge) bonding orbitals and appears as a shoulder in the computational Si­[F]:L 23 VV AES. Except for the peak at 73.4 eV, the Si­[F]:L 23 VV AES of FSMSE (Figure c) is similar to the Si:L 23 VV AES of SiF 4 (Figure e). , Furthermore, the Si atom of SiF 4 can be regarded as a model of the Si­[F] site in FSMSE . Thus, we have assigned the five Si­[F]:L 23 VV Auger peaks of FSMSE seen in 30–71 eV (Figure c) according to an assignment result for SiF 4 by Aksela et al and a somewhat-revised assignment result based on ab initio MO calculations of SiF 4 by Tarantelli et al , A similar calculation of FSMSE is very difficult because FSMSE is much larger in molecular size than SiF 4 . , …”

“…Thus, the site-specificity reduction at the Si­[Cl] site of CSMSE is considered to take place during the transient period between the Si­[Cl]:L 23 VV Auger electron emission and the subsequent fragmentation. If a part or the whole of the site-specific fragmentation came from ultrafast dissociation, , some specificity reduction by the F → Cl substitution should occur during the transient period between the photoelectron and Auger electron emissions. Accordingly, the ultrafast dissociation is unlikely to play a great role in the site-specific fragmentation.…”

“…24 The Si-[Me]:L 23 VV Auger peaks in 67−83 eV (Figures 3b and 4b 3c) is similar to the Si:L 23 VV AES of SiF 4 (Figure 3e). 20,26 Furthermore, the Si atom of SiF 4 can be regarded as a model of the Si[F] site in FSMSE. 27 Thus, we have assigned the five Si[F]:L 23 VV Auger peaks of FSMSE seen in 30−71 eV (Figure 3c) according to an assignment result for SiF 4 by Aksela et al 26 and a somewhat-revised assignment result based on ab initio MO calculations of SiF 4 by Tarantelli Calibration of the binding-energy scale has been performed using a high-resolution Si:2p PES reported previously.…”