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 $T_d$ point group. High‐resolution measurements, which indicate an associated complex of lower symmetry, possibly $D_{\text{2h}}{\mathrm{,\; C}}_{\text{2h}}$ , or $C_{\text{2υ}}$ , 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 ${\mathrm{(\rho }}_s)$ for the ${\nu }_1$ fundamental is 0.008, substantially greater than for ${\nu }_1$ 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 ${\rho }_s\text{\hspace{0.17em}=\hspace{0.17em}0.75}$ as expected. Earlier results are reviewed and reinterpreted in terms of the new dimer model for liquid TiCl₄.