Heats of Formation of Xenon Fluorides and the Fluxionality of XeF6 from High Level Electronic Structure Calculations

详细信息    查看全文

• 作者：David A. Dixon ; Wibe A. de Jong ; Kirk A. Peterson ; Karl O. Christe ; and Gary J. Schrobilgen
• 刊名：Journal of the American Chemical Society
• 出版年：2005
• 出版时间：June 22, 2005
• 年：2005
• 卷：127
• 期：24
• 页码：8627 - 8634
• 全文大小：78K
• 年卷期：v.127,no.24(June 22, 2005)
• ISSN：1520-5126

文摘

Atomization energies at 0 K and heats of formation at 0 and 298 K are predicted for XeF⁺,XeF^-, XeF₂, XeF₄, XeF₅^-, and XeF₆ from coupled cluster theory (CCSD(T)) calculations with new correlation-consistent basis sets for Xe. To achieve near chemical accuracy (±1 kcal/mol), up to four corrections wereadded to the complete basis set binding energies based on frozen core coupled cluster theory energies:a correction for core-valence effects, a correction for scalar relativistic effects, a correction for first-orderatomic spin-orbit effects, and in some cases, a second-order spin-orbit correction. Vibrational zero-pointenergies were computed at the coupled cluster level of theory. The structure of XeF₆ is difficult to obtainwith the C_3v and O_h structures having essentially the same energy. The O_h structure is only 0.19 kcal/molbelow the C_3v one at the CCSD(T)/CBS level using an approximate geometry for the C_3v structure. With anoptimized C_3v geometry, the C_3v structure would probably become slightly lower in energy than the O_h one.The calculated heats of formation for the neutral XeF_n fluorides are less negative than the experimentalvalues from the equilibrium measurements by 2.0, 7.7, and 12.2 kcal/mol for n = 2, 4, and 6, respectively.For the experimental values, derived from the photoionization measurements, this discrepancy becomeseven larger, suggesting a need for a redetermination of the experimental values. Evidence is presented forthe fluxionality of XeF₆ caused by the presence of a sterically active, free valence electron pair on Xe.