Mass-independent fractionation of titanium isotopes

Forty years ago, the synthesis of ozone has revealed mass-independent fractionation (MIF) of oxygen isotopes. Among the numerous published interpretations of this ozone effect, the present paper reports that a titanium MIF observed during chemical reactions in plasma can be accounted for by one of these theoretical treatments. A gaseous mixture of TiCl₄/C₅H₁₂ carried in a glass tube by a continuous flow of N₂ was submitted to a HF discharge. Carbonaceous grains, presumably resulting from homogeneous condensation, show radial variations in Ti concentration with isotopic variations ranging from −25 to +125% for all ${}^m\mathrm{Ti}$/⁴⁸Ti isotope ratios ($m$ standing for masses 46, 47, 49 and 50). It is proposed that the reduction rates by carbon radicals, of the metastable molecules formed by the isotope exchange reactions between Ti and TiCl₄ are different if they involve distinguishable or indistinguishable isotopes. A numerical simulation reproduces the experimental isotope patterns defined by the ${}^m\mathrm{Ti}$/⁴⁸Ti isotope ratios.