Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People's Republic of China.
J Phys Chem A. 2010 Sep 23;114(37):10217-24. doi: 10.1021/jp103782r.
Investigations on the dissociation kinetics of hydrated protonium ions, (H(2)O)(2)H(+) and their deuterated species (D(2)O)(2)D(+), are reported based on the harmonic and anharmonic oscillator model using the transition state theory and ab initio calculations. We find that the dissociation of (H(2)O)(2)H(+) and (D(2)O)(2)D(+) exhibits a distinct threshold behavior due to the existence of activation energies. Moreover, the deviation between the harmonic and anharmonic dissociation rate constants becomes larger in the high energy or temperature range, with the rate constants becoming unreasonably large under the harmonic oscillator model. The isotope effect is found to become more distinct but only in the case of the anharmonic oscillator model. These results show that the anharmonic Rice-Ramsperger-Kassel-Marcus (RRKM) theory can provide a reasonably good description for the dissociation of (H(2)O)(2)H(+) and (D(2)O)(2)D(+). Furthermore, a theoretical model to demonstrate the principle of vibrational predissociation spectroscopy (VPS) is established from the viewpoint of RRKM theory and applied in determining the experimental conditions and understanding the role of the dissociation rate constant k(E) played in the VPS experiment, using (H(2)O)(2)H(+) and (D(2)O)(2)D(+) as examples.
基于过渡态理论和从头算计算，利用谐振子和非谐振子模型，研究了水合质子离子((H(2)O))(2)H(+)及其氘代物种((D(2)O))(2)D(+)的离解动力学。我们发现由于活化能的存在，(H(2)O))(2)H(+)和(D(2)O))(2)D(+)的离解表现出明显的阈行为。此外，在高能或高温范围内，谐振子和非谐振子离解速率常数之间的偏差变得更大，在谐振子模型下，速率常数变得不合理地大。发现同位素效应变得更加明显，但仅在非谐振子振子模型的情况下。这些结果表明，非谐瑞利-拉姆斯伯格-卡塞尔-马库斯（RRKM）理论可以为（H(2)O))(2)H(+)和(D(2)O))(2)D(+)的离解提供一个相当好的描述。此外，从 RRKM 理论的角度建立了一个理论模型，用于演示振动预解离光谱学（VPS）的原理，并应用于确定实验条件和理解离解速率常数 k(E)在 VPS 实验中所起的作用，以（H(2)O))(2)H(+)和(D(2)O))(2)D(+)为例。
