Silicon tetrafluoride (SiF4) and sulfur hexafluoride (SF6) 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-1, whereas that of the corresponding S-F bond is 300 kJ mol-1. Therefore, SiF4 is expected to be a more versatile sensitizing agent than SF6, 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 SiF4 (or SF6) 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 SF6, such data are not generally available for SiF4. Moreover, in the case of laser-excited experiments, there is the potential for photochemical bleaching. Again, such data have been obtained for SF6, but only a limited amount of information is available for SiF4. 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.
Aaron Sandoski and Joseph J. BelBruno, "Absorptivity of SiF4 at 1027 cm-1 for High Continuous-Wave Laser Power," Appl. Spectrosc. 50, 420-422 (1996)