The volatile species enter this orifice, undergo a free jet expan-A high-pressure sampling mass spectrometer was used to sion, and form a molecular beam. The beam passes through a detect the volatile species formed from SiO 2 at temperatures series of differentially pumped vacuum chambers and finally between 1200؇ and 1400؇C in a flowing water vapor/oxygen enters a chamber which has a pressure sufficiently low to opergas mixture at 1 bar total pressure. The primary vapor ate a quadrupole mass filter. An ionization energy of 40 eV species identified was Si(OH) 4 . The fragment ion Si(OH) 3 ؉ was used. This sampling system preserves the chemical and was observed in quantities 3 to 5 times larger than the dynamic integrity of the volatile species, even if they are conparent ion Si(OH) 4 ؉ . The Si(OH) 3 ؉ intensity was found to densable or reactive. Although absolute vapor pressures cannot have a small temperature dependence and to increase with be measured with this system, important qualitative trends can the water vapor partial pressure as expected. In addition, be observed. 9-12 SiO(OH) ؉ , believed to be a fragment of SiO(OH) 2 , wasThe SiO 2 -H 2 O reaction took place in a 22 mm ID fused observed. These mass spectral results were compared to the quartz furnace tube, typically at 1300ЊC. An oxygen stream behavior of silicon halides.with a flow rate of 233 sccm was saturated with water vapor and subsequently flowed through a disk-shaped fused quartz