Isotope Anomalies and the Isotope Exchange Equilibria

用量子统计力学方法计算了50- 2000 K温度范围内双原子分子间氧、碳、氮同位素交换反应的平衡常数，发现许多平衡常数都表现出反常的质量效应。例如，O_z与其它双原子氧化物（MO）之间的^<16>O-^<15>O、^<16>O-^<17>O、^O<16>-^<18>O和^<16>O-^<19>O交换反应的平衡常数（K_（65）、K_（67）、K_（68）、K_（69）都表现出反常的质量效应，并具有K_（67）= K_（68）等质量无关分馏（MIF）温度，当M为Ge等时，计算了交叉温度。反常质量效应与M-O力常数有关。平衡常数在中等力常数范围内表现出异常质量效应，当M为S、Rh、Ir、Rh时，C_z与其他双原子碳化合物（MC）之间的碳同位素交换反应平衡常数表现出异常质量效应。NH与其它含氮化合物（MN）的氮同位素交换反应平衡常数也表现出异常的质量效应，本文根据分子轨道理论，采用该高速缓存热力学同位素效应计算系统，计算了臭氧（O_3）与双原子氧化物（MO）之间氧同位素交换反应的平衡常数。当M为C或N时，平衡常数表现出反常质量效应，表明某些同位素交换平衡能引起反常质量效应，进而引起同位素异常。

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.