摘要
外部溶液相中B(OH)3与离子交换树脂相中B(OH)4-、B3O3(OH)52-、B3O3(OH)4-之间所发生的同位素交换反应的平衡常数K是离子交换色谱法分离硼同位素研究中的基本参数之一,但难以用实验手段精确测定。本研究利用密度泛函理论(DFT)在B3LYP/6—31G理论水平上计算了气态下B(OH)3、B(OH)4-等的振动频率,用计算得到的频率,基于Urey模型求得B(OH)3、B(OH)4-、B3O3(OH)52-、B3O3(OH)4-的简约配分函数比(RPFR),进而得到同位素交换反应平衡常数。结果表明,B(OH)3和B(OH)4-间的同位素效应显著,其平衡常数K在25℃时为1.025 7,B(OH)3与B3O3(OH)52-和B3O3(OH)4-反应的平衡常数较小,分别约为1.017 2和1.008 4。
The equilibrium constant K for isotopic exchange reactions between boric acid B（OH）3 in the external solution and the main species of B（OH）4^-,B3O3（OH）5^2-and B3O3（OH）4^-formed in an ion-exchange resin is one of the fundamental parameters in the study of boron isotopes separation by ion-exchange chromatography.Unfortunately,it is very difficult to determine the K value accurately from experiments.Density function theory（DFT）calculations were used to compute the vibrational frequencies of boron isotopomers of the gas-phase B（OH）3 and B（OH）^4-at the B3LYP/6—31G level.The values of reduced partition function ratio（RPFR）of the four boron species,B（OH）3,B（OH）^4-,B3O3（OH）52-and B3O3（OH）^4-,were estimated following Urey＇s model,using the calculated frequencies obtained from DFT calculation.The equilibrium constant K of isotopic exchange reactions were theoretically obtained as the ratio of the RPFRs of two boron species.The results implied that the isotopic effect between B（OH）3 and B（OH）4-was remarkable with a calculated equilibrium constant K of 1.025 7 at 25 ℃.However,these K valcues for the reactions between B（OH）3 with other two species,B3O3（OH）5^2-and B3O3（OH）4,were smaller around 1.017 2 and 1.008 4,respectively.
出处
《同位素》
CAS
2011年第2期107-112,共6页
Journal of Isotopes
基金
反应堆燃料及材料重点实验室基金(9140C7005010804)
关键词
离子交换色谱
硼同位素
平衡常数
ion-exchange chromatography
boron isotopes
equilibrium constant
