Department of Chemistry, University of Helsinki, P.O. Box 55, FIN-00014, Finland.
J Phys Chem A. 2012 Jun 7;116(22):5305-11. doi: 10.1021/jp302911p. Epub 2012 May 23.
The complexes of formic acid (HCOOH, FA) with carbon dioxide are studied by infrared spectroscopy in an argon matrix. Two trans-FA···CO(2) and one cis-FA···CO(2) complexes are experimentally identified while the calculations at the MP2(full)/6-311++G(2d,2p) level of theory predict one more minimum for the cis-FA···CO(2) complex. The complex of the higher-energy conformer cis-FA with CO(2) is prepared by vibrational excitation of the ground-state trans-FA conformer combined with thermal annealing. The lifetime of the cis-FA···CO(2) complex in an argon matrix at 10 K is 2 orders of magnitude longer than that of the cis-FA monomer. This big difference is explained by the computational results which show a higher stabilization barrier for the complex. The solvation effects in solid argon are theoretically estimated and their contribution to the stabilization barriers of the higher-energy species is discussed. The relative barrier transmissions for hydrogen tunneling in the cis-FA···CO(2) complex and cis-FA monomer are in good agreement with the experimental decay rates.
通过在氩基质中进行的红外光谱研究，研究了甲酸（HCOOH，FA）与二氧化碳的配合物。实验中鉴定出了两种反式 FA···CO（2）和一种顺式 FA···CO（2）配合物，而在 MP2（全）/6-311++G（2d，2p）理论水平的计算预测顺式 FA···CO（2）配合物还有一个更低的能量点。通过对基态反式 FA 构象进行振动激发并结合热退火，制备了具有更高能量的顺式 FA 与 CO（2）的配合物。在 10 K 的氩基质中，顺式 FA···CO（2）配合物的寿命比顺式 FA 单体长 2 个数量级。这一巨大差异可以通过计算结果来解释，计算结果表明配合物的稳定化势垒更高。理论上估算了在固体氩中的溶剂化效应，并讨论了它们对高能物质稳定化势垒的贡献。在顺式 FA···CO（2）配合物和顺式 FA 单体中氢隧穿的相对势垒传输率与实验衰减率非常吻合。
