Abstract

Silicon tetrafluoride (SiF<sub>4</sub>) and sulfur hexafluoride (SF<sub>6</sub>) are widely used as sensitizing agents in photochemical experiments in the infrared region of the spectrum. These experiments include chemical vapor deposition, powder formation (for a review see Ref. 1), and kinetics. The energy of the Si-F bond is 610 kJ mol<sup>-1</sup>, whereas that of the corresponding S-F bond is 300 kJ mol<sup>-1</sup>. Therefore, SiF<sub>4</sub> is expected to be a more versatile sensitizing agent than SF<sub>6</sub>, since the relatively high Si-F bond energy allows for greater radiative energy input and higher effective reaction temperatures. The high effective temperatures attained with the use of SiF<sub>4</sub> (or SF<sub>6</sub>) necessitate the study of the absorptivities of these materials, since that quantity is known to be temperature dependent. Unfortunately, although some experimental results have been reported for SF<sub>6</sub>, such data are not generally available for SiF<sub>4</sub>. Moreover, in the case of laser-excited experiments, there is the potential for photochemical bleaching. Again, such data have been obtained for SF<sub>6</sub>, but only a limited amount of information is available for SiF<sub>4</sub>. In this study, we report on the absorptivity as a function of sample pressure (temperature) and as a function the continuous-wave (cw) laser power for conditions typically employed in sensitized infrared-driven chemical processes. It may be readily observed from the presented data that the absorptivity decreases with increasing laser power and that a limiting temperature is reached for increasing sample pressure at a constant laser power.

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