Interaction of H(D) Atoms with Octadecylsiloxane Self-Assembled Monolayers on the Si(100) Surface

ion is followed by addition of a deuterium atom to the alkyl radical These stepsare shownschematically inFigure5. Because the flux of deuterium atoms is essentially constant, the overall reaction is assumed to be first order in the concentration of C-H bonds. Also, because reaction 2 is the addition of two radicals, it is assumed to occur rapidly; thus, reaction 1 is the rate-limiting step. With these assumptions, the kinetics of H/D exchange simplifies to the kinetics of hydrogen abstraction, reaction 1. The rate of disappearance of C-H bonds is described by the following equation: which has the following solution wherebracketsdenote concentrations,σ is thecross section for exchange, and J(D) is the flux of deuterium atoms. (17) Dote, J. L.; Mowery, R. L. J. Phys. Chem. 1988, 92, 1571. (18) Blaudez, D.; Buffeteau, T.; Castaings, N.; Desbat, B.; Turlet, J.-M. J. Chem. Phys. 1996, 104, 9983. (19) MacPhail, R. A.; Strauss, H. L.; Snyder, R. G.; Elliger, C. A. J. Phys. Chem. 1984, 88, 334. (20) Robinson, G. N.; Freedman, A.; Graham, R. L. Langmuir 1995, 11, 2600. Figure 3. Close-up of the C-D and C-H stretch region as a function of deuterium exposure. Figure 4. HREELS peak areas for the C-H (b) and C-D (2) stretch as a function of deuterium exposure. D + tC-H f tC + HDv (1)