J. Phys. Chem. A 2009, 113, 7267–7274
7267
Theoretical Calculation of Separation Factors for Boron Isotopic Exchange between BF3 and BF3 · C6H5OCH3† Tao Lin,‡,§ Weijiang Zhang,‡ and Lichang Wang*,§ School of Chemical Engineering and Technology, Tianjin UniVersity, Tianjin 300072, China, and Department of Chemistry and Biochemistry, Southern Illinois UniVersity, Carbondale, Illinois 62901 ReceiVed: NoVember 24, 2008; ReVised Manuscript ReceiVed: December 16, 2008
The separation factors (or equilibrium constants) for boron isotopic exchange reaction 10BF3 + 11BF3 · C6H5OCH3 a 11BF3 + 10BF3 · C6H5OCH3 were obtained from MP2/6-31+G(d,p) and B3LYP/6-31+G(d,p) calculations. New scaling factors, single and multiple, were derived from the harmonic frequencies through the leastsquares fit for BF3 and C6H5OCH3. The use of multiple scaling factors in the case of C6H5OCH3 led to significant improvement in the calculated frequencies over using a single scaling factor. There exists a negligible difference in the separation factors obtained by using the harmonic and the scaled frequencies of the same method, and in those obtained by using different methods. The calculated separation factors for the boron isotopic exchange reaction at 273.15, 293.15, and 298.15K are 1.039, 1.036, and 1.035, respectively, which are in excellent agreement with the experimental values, 1.041 ( 0.002, 1.030 ( 0.002, and 1.035 ( 0.003. This study demonstrated the promise of using DFT (B3LYP) to obtain separation factors for the reactions where the interactions are weaker than covalent bonds but stronger than van der Waals interactions, and consequently to search for better complexation agents than C6H5OCH3 for the isotopic separation of BF3. 1. Introduction Boron has two stable isotopes, 10B and 11B, with a natural concentration of 19.9% and 80.1%, respectively.1 Because of the superior ability of 10B in absorbing neutrons (3.837 × 10-25 m2) compared to that of 11B (
