Dissociation dynamics of energy-selected hexamethyldisilane ions and the heats of formation of trimethylsilyl(1+) ion ((CH3)3Si+) and trimethylsilyl radical ((CH3)3Si)

Szepes, László; Baer, Tomas

doi:10.1021/ja00314a002

Cited by 42 publications

(23 citation statements)

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“…63,64 This value is in agreement with another study by Szepes and Baer who determined a heat of formation of −226.2 ± 4.5 kJ/mol. 65 Our calculated value of −225.1 kJ/mol is closer to the latter value. Figure 1 depicts the trend in ΔH°f for the H 4−x Me x Si series where x = 0−4.…”

Section: ■ Results and Discussionsupporting

confidence: 72%

Computational Thermochemistry of Mono- and Dinuclear Tin Alkyls Used in Vapor Deposition Processes

2019

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Hexamethylditin has been reported to be a more effective precursor compared to monotin analogs in hybrid molecular beam epitaxy depositions of perovskite oxides. To understand the differences, a library of 68 monotin-and ditincontaining molecules bearing hydrido and/or carbon-based ligands was generated, and their structures were optimized using density functional theory. On the basis of a modified W1-F12 composite thermochemical method, thermochemical data (enthalpy of formation, entropy, and heat capacity) were calculated for each structure over a range of temperatures (298− 5000 K). The application of the modified W1-F12 method to heavy element compounds was benchmarked against existing experimental and computational studies of mononuclear hydrido, alkyl, and mixed hydridoalkyl complexes of silicon, germanium, and tin. The library of thermodynamic data was used in partial equilibrium calculations from 300 to 1500 K to determine gas phase compositions resulting from the pyrolysis of tetramethyltin and hexamethylditin at 10 −6 and 760 Torr.

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Section: ■ Results and Discussionsupporting

confidence: 72%

Computational Thermochemistry of Mono- and Dinuclear Tin Alkyls Used in Vapor Deposition Processes

2019

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“…The broadening of the two fragment ion peaks from HMDS has been previously shown to be due to the slow dissociation of the parent ion. 16,17 Weak peaks were also observed at m/z = 58 and 72, as illustrated in the inset picture of Fig. 1.…”

Section: Resultsmentioning

confidence: 75%

“…In our experiments with HMDS in the reactor, the intensity ratio of the peak at m/z = 204 to that at m/z = 203 ranges from 41.8 to 102.5%, depending on the filament temperature and filament on-time. The other source that is contributing the intensity of the peak at m/z = 204 is believed to be octamethyltrisilane produced from reaction (16). The decamethyltetrasilane from reaction ( 17) was observed very weakly in the mass spectrum.…”

Section: Decomposition Of Hmds On the W Filamentmentioning

confidence: 99%

Decomposition of hexamethyldisilane on a hot tungsten filament and gas-phase reactions in a hot-wire chemical vapor deposition reactor

Shi

Tong

et al. 2008

Phys. Chem. Chem. Phys.

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To study the effect of an Si-Si bond on gas-phase reaction chemistry in the hot-wire chemical vapor deposition (HWCVD) process with a single source alkylsilane molecule, soft ionization with a vacuum ultraviolet wavelength of 118 nm was used with time-of-flight mass spectrometry to examine the products from the primary decomposition of hexamethyldisilane (HMDS) on a heated tungsten (W) filament and from secondary gas-phase reactions in a HWCVD reactor. It is found that both Si-Si and Si-C bonds break when HMDS decomposes on the W filament. The dominance of the breakage of Si-Si over Si-C bond has been demonstrated. In the reactor, the abstraction of methyl and H atom, respectively, from the abundant HMDS molecules by the dominant primary trimethylsilyl radicals produces tetramethylsilane (TMS) and trimethylsilane (TriMS). Along with TMS and TriMS, various other alkyl-substituted silanes (m/z = 160, 204, 262) and silyl-substituted alkanes (m/z = 218, 276, 290) are also formed from radical combination reactions. With HMDS, an increasing number of Si-Si bonds are found in the gas-phase reaction products aside from the Si-C bond which has been shown to be the major bond connection in the products when TMS is used in the same reactor. Three methyl-substituted 1,3-disilacyclobutane species (m/z = 116, 130, 144) are present in the reactor with HMDS, suggesting a more active involvement from the reactive silene intermediates.

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“…It is noticed that the mass peaks of the parent ion and Me 3 Si + fell off slowly in intensity leading to an asymmetric shape with several additional small peaks. This was due to kinetic shift caused by slow dissociation of the HMDS parent ion 44,45 and the isotopes 29 Si, 30 Si, and 13 C. The mass spectra from the room temperature to 1120 K were essentially the same and showed no extra mass peaks (also indicating that HMDS from the heated microreactor was sufficiently cooled after expansion cooling (<200 K), 31,37 and its photoionization fragmentation stayed about constant due to its modest temperatures in the molecular beam 36 ). Thermal decomposition of HMDS was not observed at temperatures from 298 to 1120 K in the short residence time scale of this study.…”

Section: Experiments and Computation Methodsmentioning

confidence: 96%

Mechanistic Study of Thermal Decomposition of Hexamethyldisilane by Flash Pyrolysis Vacuum Ultraviolet Photoionization Time-of-Flight Mass Spectrometry and Density Functional Theory

et al. 2019

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Thermal decomposition of hexamethyldisilane (HMDS) was studied from room temperature to 1310 K using flash pyrolysis vacuum ultraviolet single-photon ionization time-of-flight mass spectrometry (VUV-SPI-TOFMS). Decomposition pathways of HMDS and initial reaction intermediates were also investigated using density functional theory (DFT) at the B3LYP/6-311++G(d,p) level. Unimolecular decomposition reactions of HMDS involving Si–Si and Si–C bond cleavage, as well as decomposition producing Me4Si and :SiMe2 via a three-centered elimination, were determined as the initiation reactions. Me3SiSi(Me)2 •, Me4Si, Me3Si•, and :SiMe2 were major products of the initiation reactions. These initial products were apt to decompose by homolytic reactions. Me2SiCH2, :SiMe2, and other silene/silylene intermediates preferred decomposing through molecular eliminations. Both homolytic and molecular elimination reactions are important in the pyrolysis of HMDS.

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Dissociation dynamics of energy-selected hexamethyldisilane ions and the heats of formation of trimethylsilyl(1+) ion ((CH3)3Si+) and trimethylsilyl radical ((CH3)3Si)

Cited by 42 publications

References 0 publications

Computational Thermochemistry of Mono- and Dinuclear Tin Alkyls Used in Vapor Deposition Processes

Computational Thermochemistry of Mono- and Dinuclear Tin Alkyls Used in Vapor Deposition Processes

Decomposition of hexamethyldisilane on a hot tungsten filament and gas-phase reactions in a hot-wire chemical vapor deposition reactor

Mechanistic Study of Thermal Decomposition of Hexamethyldisilane by Flash Pyrolysis Vacuum Ultraviolet Photoionization Time-of-Flight Mass Spectrometry and Density Functional Theory

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