Journal
ZEITSCHRIFT FUR PHYSIKALISCHE CHEMIE-INTERNATIONAL JOURNAL OF RESEARCH IN PHYSICAL CHEMISTRY & CHEMICAL PHYSICS
Volume 229, Issue 5, Pages 691-708Publisher
WALTER DE GRUYTER GMBH
DOI: 10.1515/zpch-2014-0640
Keywords
TEOS; VRC-TST; ab initio; Rate Constant
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Funding
- US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences [DE-AC02-06CH11357]
- National Research Foundation (NRF), Prime Minister's Office, Singapore
- Engineering and Physical Sciences Research Council [1233854] Funding Source: researchfish
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In this paper we use variable reaction coordinate variational transition state theory (VRC-TST) to calculate the reaction rate constants for the two reactions, R1: (OH)(3)SiOCH2 + CH3 reversible arrow (OH)(3)SiOC2H5, and R2: CH2OH + CH3 reversible arrow C2H5OH. The first reaction is an important channel during the thermal decomposition of tetraethoxysilane (TEOS), and its rate coefficient is the main focus of this work. The second reaction is analogous to the first and is used as a basis for comparison. The interaction energies are obtained on-the-fly at the CASPT2(2e,2o)/cc-pVDZ level of theory. A one-dimensional correction to the sampled energies was introduced to account for the energetic effects of geometry relaxation along the reaction path. The computed, high-pressure rate coefficients were calculated to be, R1: k(1) = 2.406x10(-10)T(-0.301) exp(-271.4/T) cm(3) molecule(-1) s(-1) and R2: k(2) = 1.316x10(-10)T(-0.189) exp(-256.5/T) cm(3) molecule(-1) s(-1). These rates differ fromeach other by only 10%-30% over the temperature range 300-2000 K. A comparison of the computed rates with experimental data shows good agreement and an improvement over previous results. The pressure dependency of the reaction R1 is explored by solving a master equation using helium as a bath gas. The results obtained show that the reaction is only weakly pressure dependent over the temperature range 300-1700 K, with the predicted rate constant being within 50% of its high-pressure limit at atmospheric pressure.
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