rangements of phosphine ligands and require passage through several intermediate TTP topologies in order to return to the ground-state arrangement with two eclipsed prismatic phosphines and a capping phosphine on the opposite prismatic face.
Conclusions13C and 31P CP/MAS NMR data obtained over a range of temperatures are consistent with a tricapped-trigonal-prismatic structure for W(PMe3)3H6, with two phosphine ligands in eclipsed prismatic sites and the third in the opposite capping site. In contrast to the results of previous crystallographic studies on such compounds, the NMR spectra suggest that the two prismatic phosphine ligands in each molecule are slightly inequivalent. At temperatures above ambient, interchange of ligand functionality for the phosphine ligands is observed by magnetization-transfer experiments and, at still higher temperatures, by simulation of the exchange-broadened NMR line shapes observed experimen-tally. Rate data from the two methods of analysis suggest Arrhenius activation parameters for ligand functionality interchange of £a = 148.8 ± 15 kJ mol'1 and A -6.6 X 1023 s'1. The rate of functionality interchange reaches ca. 2000 Hz by the decomposition point of the material (381 K). A mechanism for this exchange has been proposed, involving the "double rearrangement" TTP(ground state) -MSA ^TTP(excited state) **=* MSA 5=* TTP(ground state)In this mechanism slight stretches of the polytypal edges result in interchange of ligand functionality without the need for unfavorable spatial permutation of the phosphine ligands.Acknowledgment. J. Pound is thanked for a sample of W-(PMe3)3H6, and Drs.
Etching of the cathodes in magnetron sputtering determines the plasma discharge properties and deposition efficiency. In high-power and high-ionization discharges, etching becomes more complicated, resulting in inaccurate results if the conventional models are still used. This work aims at establishing an accurate dynamic model for high-power and high-ionization discharges by combining the cellular automata (CA) method and particle-in-cell/Monte Carlo collision (PIC/MCC) method, in which all the interactions pertaining to the etching morphology, plasma density, electric field, and magnetic field are considered. In high-power discharges such as continuous high-power magnetron sputtering (C-HPMS), strong self-sputtering and intense gas rarefaction stemming from the high temperature in the vicinity of the target influence the etching behavior. Compared to the experimental results, the morphology simulated by the dynamic etching model shows an error of only 0.8% in C-HPMS, which is much less than that obtained by the traditional test-electron Monte Carlo (MC) method (10.1%) and static PIC/MCC method (4.0%). The dynamic etching model provides more accurate results to aid the development and industrial application of high-power magnetron sputtering.
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