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

Abstract

Dissociative multiple photoionization processes of dimethylsilane (H2Si(CH3)2) have been investigated in the valence and Si(2p) core level photoexcitation/photoionization regions by time-of-flight (TOF) mass spectrometry coupled to synchrotron radiation, operated in both the photoelectron−photoion coincidence (PEPICO) and photoion−photoion coincidence (PIPICO) modes. Two group absorption bands below and above the Si(2p3/2) threshold 106.51 eV are observed in both total photoion and PIPICO yield curves. Various monocations of H n +(n = 1−3), CH n +(n = 0−4), C2H n +(n = 1−3), SiH n +(n = 0−3), SiCH n +(n = 0−5), SiC2H n +(n = 0−7) are observed, the yields depending on the excitation energy. In the valence ionization region, especially E < 30 eV, extrusions of H, H2, CH3, and of CH4 (or H + CH3) and CH3 + H2 (or H + CH4), are predominantly observed leading to the formation of SiC2H n + (n = 6, 7) and SiCH n + (n = 3−5), respectively, whereas in the Si(2p) excitation and ionization regions, ionic fragments of smaller masses such as H+, CH3 +, Si+, and SiCH3 + are relatively abundant in the PEPICO spectra. Bond-selective fragmentation processes occur in the two absorption regions. An ab initio calculation was also carried out to predict discrete excitation energies and their modes corresponding to the transitions from the core to valence and Rydberg orbitals.

Effect of substrates on the molecular orientation of silicon phthalocyanine dichloride thin films

“…Peaks A have maximum intensities at grazing incidence, while peaks B have maximum intensities at near-normal incidence. In order to assign the origins of these peaks, we have conducted theoretical calculations on the unoccupied molecular orbitals in the core excited states (equivalent core approximation) [24] for SiPcCl 2 molecules using the self-consistent field molecular orbital (SCF-MO) method with the 3-21G basis set [25,26]. The most stable molecular structures were obtained by optimizing the total potential energy.…”

Synchrotron radiation studies of the orientation of thin silicon phthalocyanine dichloride film on HOPG substrate

“…In order to assign those peaks to correlative chemical bonds, we calculated the unoccupied molecular orbital in the core excited states (Equivalent core approximation) [16] for SiPcCl 2 molecule using the selfconsistent field molecular orbital (SCF-MO) method with 3-21G basis set. Most stable molecular structures were obtained by optimizing the total potential energy.…”