Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323, USA.
Phys Chem Chem Phys. 2012 May 14;14(18):6219-24. doi: 10.1039/c2cp23892f. Epub 2012 Feb 8.
Two dimensional vibrational echo spectra of oxalate in the carboxylate asymmetric stretch region in D(2)O show two transitions having anomalously slow spectral diffusion and a third transition having relaxation properties typical of the free carboxylate ion. Quantitative analysis of the frequency shifts of the carboxylate asymmetric stretch modes caused by a singly charged cation in the oxalate hydration shell supports that ion pairs can be responsible for these new transitions. Experimental evidence and DFT calculations are consistent with oxalate forming a mixture of "side-on" and "end on" contact ion pairs wherein the carboxylate groups are protected from mobile heavy water molecules.
D2O 中草酸盐羧酸不对称伸缩区域的二维振动回波谱显示出两个具有异常缓慢光谱扩散的跃迁和第三个具有自由羧酸离子典型弛豫特性的跃迁。对在草酸盐水合壳中单电荷阳离子引起的羧酸不对称伸缩模式的频率位移的定量分析支持离子对可能是这些新跃迁的原因。实验证据和 DFT 计算与草酸盐形成“侧接”和“端接”接触离子对的混合物一致，其中羧酸基团受到保护，免受可移动重水分子的影响。
