H2CO3 Forms via HCO3− in Water

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• 作者：Andrs Stirling ; Imre Ppai
• 刊名：Journal of Physical Chemistry B
• 出版年：2010
• 出版时间：December 23, 2010
• 年：2010
• 卷：114
• 期：50
• 页码：16854-16859
• 全文大小：265K
• 年卷期：v.114,no.50(December 23, 2010)
• ISSN：1520-5207

文摘

According to the generally accepted picture of CO₂ dissolution in water, the formation of H₂CO₃ proceeds in a single step that involves the attack of a water oxygen on the CO₂ carbon in concert with a proton transfer to a CO₂ oxygen. In the present work, a series of ab initio molecular dynamics simulations have been carried out along with the metadynamics technique which reveals a stepwise mechanism: the reaction of a water molecule with CO₂ yields HCO₃⁻ as an intermediate and a hydronium ion, whereas the protonation of the CO₂ moiety occurs in a separate step representing a well-defined activation barrier toward the H₂CO₃ molecule. This alternative scenario was already taken into consideration decades ago, but subsequent experiments and calculations have given preference to the concerted mechanism. Employing extended periodic models of the CO₂−water system that mimic the bulk aqueous environment, the present simulations yield the complete free energy profile of the stepwise mechanism and provide a detailed microscopic mechanism of the elementary steps. HCO₃⁻ formation is found to be the rate-determining step of the entire CO₂ hydration process.