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Absolute rates of vacuum-ultraviolet photochemical deposition of thin films from high molecular weight siloxane and phthalate precursors have been measured in molecular beam experiments using sensitive quartz crystal microbalance detection. Depositions were carried out under conditions of surface temperature and molecular flux for which bulk condensation would not occur.The deposition rate demonstrated an inverse dependence on substrate temperature, weak dependence on photolysis wavelength (below 200 nm), a sublinear dependence on precursor flux, and a significant dependence on substrate composition, manifested beyond monolayer coverage. The kinetic behaviors of the deposition rate could be described by a simple mechanism in the spirit of the Langmuir model of adsorption.

The rate of reaction of solid carbon with atomic oxygen impacting at a translational energy of approximately 100 kJ/mole has been measured at carbon surface temperatures ranging from 300-400 K. The magnitudes of the rates and the apparent activation energy (with respect to the carbon surface temperature) of approximately 15 kJ/mole are in good agreement with rates reported in the literature for the reaction of atomic oxygen with carbon at thermal impact energies. The relatively good agreement among these two sorts of laboratory measurements and reaction rates inferred from exposure of carbon to the low Earth orbit environment on various flights of the Space Shuttle suggests that there is little or no dependence of the rate of this reaction on the translational energy with which the atomic oxygen strikes the carbon surface. Nomenclature C' =rate of carbon loss in atoms/cm 2 -s %D = degree of dissociation of O 2 into 2 O atoms as defined by Eq. (5) Fj = flux of species / in particles/cm 2 -s, where /= O, O 2 A£T = heat of reaction in units of kJ/mole 7 = intensity of incident light transmitted through target 7 0 = intensity of incident light m c = mass of a carbon atom, ~2x 10~2 3 g NJ = number density in units of particles/cm 3 , where / = O, 0 2 P = reaction probability for the O + C reaction P d = probability of dissociative electron-impact ionization R = ratio of reaction probability of C with O 2 to that of C with O Si =mass spectrometer signal in amps, where / = O, O 2 T = absolute temperature of target, K / = thickness of carbon removed by chemical reaction, cm y = ratio of atomic to molecular oxygen in the mass spectrometer ionizer r] = ratio of S 0 /S 0 , resulting from dissociative ionization of0 2 0 0 = fluence of atomic oxygen in atoms/cm 2 p = carbon density in g/cm 3 a, = electron impact ionization cross section, where / = O, 0 2 Subscripts c = crystalline form of element g = gaseous form of element Superscripts ( )* = translation excitation of 500 kJ/mole

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