INVESTIGATIONS OF THE REACTIONS OF TRIETHOXYCHLOROSILANE, TETRAETHOXYSILANE, TRIETHOXYSILANE, TRICHLOROSILANE AND TRIFLUOROSILANE WITH ATOMIC OXYGEN IN THE ELECTRONIC GROUND-STATE [O(P-3)]

The rates of the reactions of triethoxychlorosilane, tetraethoxysilane , triethoxysilane and trifluorosilane with atomic oxygen in the ground state [O(P-3)] were measured in a discharge flow system with mass spe ctrometric detection. The measurements were performed in an excess of O-atoms in the temperature range 293 K < T < 773 K. Only the rate coef ficients of trifluorosilane were determined in a smaller temperature i nterval from 573 K to 773 K. The obtained second order rate constants can be represented by straight lines in an Arrhenius plot. They can be approximated by the following expressions: Triethoxychlorosilane, (C2 H5O)(3)SiCl: k(T) = (3.8 +/- 0.8) X 10(12) X exp (- (1490 +/- 150 K/T) cm(3)mol(-1)s(-1). Tetraethoxysilane, (C2H5O)(4)Si: k(T) = (2.7 +/- 0 .5) X 10(12) X exp (- (1320 +/- 130) K/T) cm(3)mol(-1)s(-1). Triethoxy silane, (C2H5O)(3)SiH: k(total) = k(Si-H) + k(C-H) k(total) = 7 X 10(1 2) exp (-1840 K/T) + 4 X 10(12) exp (-1490 K/T) cm(3)mol(-1)s(-1). Err or limits: Frequency factor +/- 25%, activation energy +/- 15%. Triflu orosilane, F3SiH: k(T) = (5 +/- 2) X 10(12) X exp (- (2350 +/- 300) K/ T) cm(3)mol(-1)s(-1). The resulting activation energies are for trieth oxychlorosilane with O-atoms 12.4 kJ/mol, for tetraethoxysilane 11.0 k J/mol, for triethoxysilane 15 kJ/mol (attack at Si-H bond) and 12 kJ/m ol (attack at alkoxysidechain) and for trifluorosilane 20 kJ/mol. For the reaction of trichlorosilane with O(P-3)-atoms a product analysis i n the now system was performed. Here Cl-atoms, Cl-2-molecules and HCl were found giving a hint for the reaction mechanism. The data of the p resent publication together with data from previously performed measur ements give a rather complete picture of the behaviour of silanes with strong electronegative substituents.