Ab initio chemical kinetics for the unimolecular decomposition of Si2H5 radical and related reverse bimolecular reactions. Issue 4 (7th October 2013)

• Record Type: Journal Article
• Authors: Wu, Shang‐Ying; Lee, Yun‐Min; Wu, Jong‐Shinn; Lin, Ming‐Chang
• Is Part Of: International journal of quantum chemistry. Volume 114:Issue 4(2014:Feb. 15)
• Page Start: 278
• Page End: 288
• Publication Date: 2013-10-07
• Subjects: Quantum chemistry -- Periodicals; 541.28
• DOI: 10.1002/qua.24557
• Languages: English
• ISSNs: 0020-7608

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <p>For plasma enhanced and catalytic chemical vapor deposition (PECVD and Cat‐CVD) processes using small silanes as precursors, disilanyl radical (Si<sub>2</sub>H<sub>5</sub>) is a potential reactive intermediate involved in various chemical reactions. For modeling and optimization of homogeneous a‐Si:H film growth on large‐area substrates, we have investigated the kinetics and mechanisms for the thermal decomposition of Si<sub>2</sub>H<sub>5</sub> producing smaller silicon hydrides including SiH, SiH<sub>2</sub>, SiH<sub>3, </sub> and Si<sub>2</sub>H<sub>4</sub>, and the related reverse reactions involving these species by using <italic>ab initio</italic> molecular‐orbital calculations. The results show that the lowest energy path is the production of SiH + SiH<sub>4</sub> that proceeds via a transition state with a barrier of 33.4 kcal/mol relative to Si<sub>2</sub>H<sub>5</sub>. Additionally, the dissociation energies for breaking the SiSi and HSiH<sub>2</sub> bonds were predicted to be 53.4 and 61.4 kcal/mol, respectively. To validate the predicted enthalpies of reaction, we have evaluated the enthalpies of formation for SiH, SiH<sub>2</sub>, HSiSiH<sub>2</sub>, and Si<sub>2</sub>H<sub>4</sub>(<italic>C</italic><sub>2h</sub>) at 0 K by using the isodesmic reactions, such as <sup>2</sup>HSiSiH<sub>2</sub> + <sup>1</sup>C<sub>2</sub>H<sub>6</sub>→<sup>1</sup>Si<sub>2</sub>H<sub>6</sub> + <sup>2</sup>HCCH<sub>2</sub> and <sup>1</sup>Si<sub>2</sub>H<sub>4</sub>(<italic>C</italic><sub>2h</sub>) + <sup>1</sup>C<sub>2</sub>H<sub>6</sub> → <sup>1</sup>Si<sub>2</sub>H<sub>6</sub> + <sup>1</sup>C<sub>2</sub>H<sub>4</sub>. The results of SiH (87.2 kcal/mol), SiH<sub>2</sub> (64.9 kcal/mol), HSiSiH<sub>2</sub> (98.0 kcal/mol), and Si<sub>2</sub>H<sub>4</sub> (68.9 kcal/mol) agree reasonably well previous published data. Furthermore, the rate constants for the decomposition of Si<sub>2</sub>H<sub>5</sub> and the related bimolecular reverse reactions have been predicted and tabulated for different T, P‐conditions with variational Rice–Ramsperger–Kassel–Marcus (RRKM) theory by solving the master equation. The result indicates that the formation of SiH + SiH<sub>4</sub> product pair is most favored in the decomposition as well as in the bimolecular reactions of SiH<sub>2</sub> + SiH<sub>3</sub>, HSiSiH<sub>2</sub> + H<sub>2</sub>, and Si<sub>2</sub>H<sub>4</sub>(<italic>C</italic><sub>2h</sub>) + H under T, P‐conditions typically used in PECVD and Cat‐CVD. © 2013 Wiley Periodicals, Inc.</p> </abstract>