Unusual isotope effects of molybdenum in chemical exchange reaction using dicyclohexano-18-crown-6

Molybdenum isotopes were fractionated in a liquid-liquid extraction system using dicyclohexano-18-crown-6 (DC18C6). The enrichment factors showed a breakdown of the conventional mass-dependent rule. Some unusual and larger isotope effects were observed in the even atomic mass isotopes, Mo-92 and Mo-94. Th, unusual features in the present study were not responsible for the field shift effect, which was regarded as a primary factor of the anomalous isotope effect in the recent theory, but were due to an anomaly on the vibrational levels. The largest isotope effect was observed in the isotope pair of Mo-94-Mo-96, it was epsilon(96,94) = 0.0086+/-0.0007, its initial aqueous phase was 0.91 M molybdenum chloride, and its organic phase was 0.2 M DC18C6 in chloroform: this was 0.0043+/-0.0004 in terms of the enrichment factor for unit mass difference.