| Research Abstract |
Equilibrium constants of oxygen, carbon and nitrogen isotopic exchange reactions between diatomic molecules were calculated in the temperature range 50-2000K on a basis of quantum statistical mechanics.
Many equilibrium constants showed the anomalous mass effects. For example, the equilibrium constants (K65, K67, K68, K69) of ^<16>O-^<15>O,^<16>O-^<17>O,^<16>O-^<18>O,and ^<16>O-^<19>O exchange reactions between O_z and the other diatomic oxides (MO) showed the anomalous mass effects, and had the mass independent fractionation (MIF) temperatures which held K67=K68 etc., and the cross over temperatures, when M was Ge etc. The anomalous mass effects were related to the M-O force constant. The equilibrium constants showed the anomalous mass effects in the intermediate force constant range.
The equilibrium constants of carbon isotope exchange reactions between C_z and the other diatomic carbon compounds (MC) showed the anomalous mass effects when M was S,Rh, Ir, etc. The equilibrium constants of nitrogen isotope exchange reactions between NH and the other nitrogen compounds (MN) also showed the anomalous mass effects when M was Al, Cl, Br, etc.
The equilibrium constants of oxygen isotope exchange reactions between ozone (O_3) and diatomic oxides (MO) were calculated on a basis of molecular orbital theory using the CAChe system for thermodynamic isotope effect-calculation. When M was C or N,the equilibrium constants showed the anomalous mass effects.
It is clear from the present work that some isotopic exchange equilibria are able to cause the anomalous mass effects, and then the isotope anomalies.
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