Dipartimento di Chimica, Università di Perugia, and CNR I.S.T.M., Via Elce di Sotto 8, 06123, Perugia, Italy.
Phys Chem Chem Phys. 2009 Nov 21;11(43):9970-5. doi: 10.1039/b914792f. Epub 2009 Sep 8.
We report the definitive assessment of a measurable (half a kJ/mol) charge-transfer (CT) component in the interaction of water with the noble gases. The CT is found to be strongly stereoselective and is mediated by a highly asymmetric, donor/acceptor concerted role of the two hydrogen atoms, which can in fact dictate the equilibrium geometry of the adducts. This finding may be of general relevance in explaining the known peculiar orientational features of water's interactions. By using an original method of partial integration of the change in electron density occurring upon the formation of Ng-water complexes (computed with accurate ab initio methods and basis sets), we map the local charge displacement along the whole intermolecular region and are thus able to appraise CT effects free of the inherent ambiguity of charge decomposition models. With this, it was possible to prove that a small CT (of the order of a couple of millielectrons at most) takes place from Ng to water. Most importantly, this CT correlates quantitatively with some unexpected "glory" quantum interference effects observed in high-resolution molecular-beam Ng-water scattering experiments that indicate a stronger bond than a pure van der Waals force. The energy stabilization associated with the observed CT does not exceed half a kJ mol(-1). The Ng-water CT is found to be strongly stereoselective and is mediated by a highly asymmetric, donor-acceptor concerted role of the two hydrogen atoms, which can in fact dictate the equilibrium geometry of the adducts. This finding may be of general relevance in explaining the known peculiar orientational features of water's interactions.
我们报告了在水与稀有气体相互作用中可测量的（半千焦每摩尔）电荷转移（CT）分量的明确评估。发现 CT 具有很强的立体选择性，由两个氢原子的高度不对称的供体/受体协同作用介导，实际上可以决定加合物的平衡几何形状。这一发现可能对解释水相互作用的已知特殊取向特征具有普遍意义。通过使用原始方法对形成 Ng-水配合物时电子密度变化进行部分积分（使用精确的从头计算方法和基组计算），我们沿着整个分子间区域绘制局部电荷位移图，从而能够评估 CT 效应，而无需电荷分解模型固有的歧义。有了这个，就有可能证明 Ng 到水中发生了少量的 CT（最多只有几毫电子）。最重要的是，这种 CT 与在高分辨率分子束 Ng-水散射实验中观察到的一些出乎意料的“荣耀”量子干涉效应定量相关，这些效应表明存在比纯范德华力更强的键。与观察到的 CT 相关的能量稳定化不超过半千焦每摩尔。发现 Ng-水 CT 具有很强的立体选择性，由两个氢原子的高度不对称的供体/受体协同作用介导，实际上可以决定加合物的平衡几何形状。这一发现可能对解释水相互作用的已知特殊取向特征具有普遍意义。
