Buchner Richard, Samani Faradj, May Peter M, Sturm Peter, Hefter Glenn
Chemistry-DOSE, Murdoch University, Murdoch, W.A. 6150, Australia.
Chemphyschem. 2003 Apr 14;4(4):373-8. doi: 10.1002/cphc.200390064.
Dielectric spectra have been measured for aqueous sodium oxalate solutions up to the saturation concentration (0.04 < or = c[mmol L-1] < or = 0.25) at 25 degrees C over the approximate frequency range 0.2 < or = v [GHz] < or = 20. The spectra exhibit a process at about 1 GHz associated with the presence of ion pairs, in addition to the dominant solvent relaxation process at about 18 GHz. Detailed analysis of the solvent dispersion amplitude indicates that the oxalate ion is highly hydrated but that its solvation sheath is "fragile", decreasing quickly with increasing solute concentration. The NaOx(aq)- ion pair is shown to be of the double-solvent-separated (2SIP) type, with an infinite dilution association constant KA = 1.04 +/- 0.02. Analysis of the ion-pair relaxation time as a function of solute concentration gave rate constants for the formation (k12 = (7.3 +/- 0.4) 10(9) L mol-1 s-1) and dissociation (k21 = (6.7 +/- 0.5) 10(8) s-1) of the ion pair. These values are reasonably close to the diffusion-controlled values predicted by the Eigen theory, consistent with a 2SIP structure for the ion pair.
在25摄氏度下，对草酸钠水溶液进行了介电谱测量，测量范围为饱和浓度（0.04 ≤ c[mmol L⁻¹] ≤ 0.25），频率范围约为0.2 ≤ v [GHz] ≤ 20。光谱显示，除了在约18 GHz处的主要溶剂弛豫过程外，在约1 GHz处还存在一个与离子对存在相关的过程。对溶剂色散幅度的详细分析表明，草酸根离子高度水合，但其溶剂化鞘层“脆弱”，随着溶质浓度的增加迅速减少。NaOx(aq)-离子对被证明是双溶剂分离（2SIP）类型，无限稀释缔合常数KA = 1.04 ± 0.02。分析离子对弛豫时间与溶质浓度的函数关系，得出离子对形成（k12 = (7.3 ± 0.4) 10⁹ L mol⁻¹ s⁻¹）和解离（k21 = (6.7 ± 0.5) 10⁸ s⁻¹）的速率常数。这些值与Eigen理论预测的扩散控制值相当接近，与离子对的2SIP结构一致。
