Infrared laser chemistry of trichlorosilane in view of silicon isotope separation

With a view toward laser isotope separation of Si, we have studied infrared multiphoton dissociation (IRMPD) of room temperature trichlorosilane, SiHCl3. Over the wavelength range investigated, multiphoton dissociation of the room temperature species exhibits a maximum efficiency at 12.6 mum and a threshold fluence of only similar to1 J/cm(2). Vibrational overtone preexcitation of SiHCl3 to the first SiH-stretch overtone (2nu(1)) prior to IRMPD results in a 10-fold increase of the dissociation yield compared to molecules with only thermal excitation. In an effort to collect the nascent SiCl2 dissociation fragments, we have tested a number of different molecules that could serve as a scavenger to convert them into a stable gaseous compound. Several of these molecules react directly with trichlorosilane after being decomposed by collisional energy transfer from vibrationally excited SiHCl3 and therefore are not suitable for a laser isotope separation process. Of the compounds tested, we find that only BCl3 scavenges SiCl2 without significant reaction with the starting material.