Kinetics and thermochemistry of SiH3 + NO and SiD3 + NO reactions: Pressure falloff and SiH3-NO bond energy

Lev N. Krasnoperov, Ilia J. Kalinovski, Jukka T. Niiranen, David Gutman

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Abstract

The reactions of silyl and silyl-d3 radicals with nitric oxide, SiH3 + NO → SiH3NO (1) and SiD3 + NO → SiD3NO (2), have been studied using pulsed excimer laser photolysis coupled with time-resolved photoionization mass spectrometry over the temperature range 301-817 K. The rate constants were measured in the ranges 0.75 × 1016 ≤ [He] ≤ 32.0 × 1016 molecules cm-3 and 301 ≤ T ≤ 611 K. Both reactions are in the pressure falloff regions considerably far from the true low-pressure limit. RRKM fittings using the Troe factorization approach yielded the low-pressure limit and high-pressure limit rate constants: k1,tri = (3.12 ± 0.12) × 10-29(T/ 298)-2.96±0.09 cm6 molecule-2 s-1, k2,tri = (9.02 ± 0.40) × 10-29(T/298)-3.36±0.11 cm6 molecule-2 s-1, k1,inf = (3.9 ± 1.1) × 10-11(T/298)-1 cm3 molecule-1 s-1, and k2,inf = (5.0 ± 1.3) × 10-11(T/298)-1 cm3 molecule-1 s-1. Equilibrium constants were measured in the temperature range 711-817 K. The standard enthalpies of reactions 1 and 2 were determined using the third law method. The bond energies determined are DH°0(H3Si-NO) = 153.7 ± 5.7 kJ mol-1, DH°298(H3Si-NO) = 158.9 ± 5.7 kJ mol-1, DH°0(D3Si-NO) = 156.1 ± 5.7 kJ mol-1, and DH°298(D3Si-NO) = 160.8 ± 5.7 kJ mol-1. This value of DH°0(H3Si-NO) is ca. 30 kJ mol-1 higher than previous estimates. Ab initio structural parameters were used to calculate the thermodynamic functions of SiH3, SiD3, SiH3NO, and SiD3NO. Both the singlet and the low-lying triplet states were taken into account for the adduct molecules. The calculated thermodynamic functions were used to obtain the standard entropies of the reactions 1 and 2: ΔS°298(rxn 1) = 143.1 J mol-1 K-1 and ΔS°298(rxn 2) = 146.0 J mol-1 K-1. The rate constants of the reaction SiH3NO + NO → products (3) were measured in the temperature range 301-611 K: k3 = (2.95 ± 0.38) × 10-13(T/298)-1.59±0.29 cm3 molecule-1 s-1.

Original languageEnglish (US)
Pages (from-to)4929-4938
Number of pages10
JournalJournal of Physical Chemistry A
Volume101
Issue number27
DOIs
StatePublished - Jul 3 1997

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry

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