MOLECULAR ASSOCIATION IN TICL4 - LASER RAMAN SPECTROSCOPY AND CHLORINE ISOTOPE EFFECTS

Evidence for molecular association of liquid TiCl4 is presented. The chlorine isotope structure in the totally symmetric fundamental cannot have originated from a simple tetrahedral molecule belonging to the Td point group. High-resolution measurements, which indicate an associated complex of lower symmetry, possibly D2h, C2h, or C2v, are interpreted in terms of a chlorine-bridged dimer structure. Additional support for an associative phenomenon rests upon some Raman data obtained for TiCl4 diluted with CCl4. The depolarization ratio (p 3) for the v1 fundamental is 0.008, substantially greater than for v1 of CCl4 (0.004), but more than an order of magnitude smaller than previously reported (0.12). The ratio drops to 0.007 for a 25 mole % solution of TiCl4 in CCl4, but depolarized fundamentals have constant values of ρ3=0.75 as expected. Earlier results are reviewed and reinterpreted in terms of the new dimer model for liquid TiCl4.