Isotope Effect in the Vibrational Frequency Spectra and Specific Heats of Sodium Hydride and Deuteride
摘要:
The prediction by the Born and von Karman lattice dynamics theory of the effect of isotopic substitution on crystal vibration frequencies has been determined by calculation of frequency spectra of sodium hydride and sodium deuteride. In each case 6690 of the lattice frequencies have been calculated with the aid of I.B.M. punched card computers. They have been chosen and weighted in such a way that the whole frequency spectra of the crystals are uniformly sampled. Both spectra exhibit acoustical branches which are nearly identical and optical branches, the frequencies of which are essentially in the ratio of the square root of two. In both cases, the optical branches extend somewhat uniformly over very broad ranges of frequencies, in marked contrast to the estimation of optical frequencies as a few monochromatic lines.
The molar heat capacities of these two compounds have been determined experimentally between 60 and 90°K with an adiabatic calorimeter and compared to corresponding curves calculated from the frequency spectra. The theoretical and experimental sets of curves possess the same general form. In both cases the deuteride values are higher than the hydride values, with the curves of the two substances diverging with increasing temperature. The theoretical curves, however, are nearly uniformly displaced from the experimental curves by about ten percent, an effect which could have arisen from an error in the repulsive force constants.
We report on hydrogen-deuterium-exchange experiments on NaH probed by thermogravimetry. From the measurements a diffusion parameter of deuterium in NaH of D=1.1×10−17 m2/s at 523 K is derived. The activation energy of tracer diffusion of D in NaH is found to be 1.0 eV. The results are hints for a diffusion process mediated by neutral hydrogen vacancies.
我们报告了通过热重法探测的 NaH 的氢-氘交换实验。根据测量结果,推导出 523 K 下氘在 NaH 中的扩散参数 D=1.1×10-17 m2/s。发现 D 在 NaH 中的示踪扩散的活化能为 1.0 eV。结果暗示了由中性氢空位介导的扩散过程。
Spectroscopy of the NaH, NaD, KH, and KD <i>X</i> <sup>1</sup>Σ<sup>+</sup> ground state by laser excited fluorescence in a high frequency discharge
作者:Marc Giroud、Odette Nedelec
DOI:10.1063/1.440721
日期:1980.11
By laser excited fluorescence of the hydrides obtained in a discharge, the ground state vibrational levels of NaH, NaD, KH, and KD have been observed up to v″=15, 20, 14, and 16, respectively, instead of v″=8, 2, 4, and 4 by conventional spectroscopy. Experimental values of Gv″, Bv″, and Dv″ are obtained. Spectroscopic parameters and RKR potential curves are calculated. In NaH and NaD, a comparison can be made with ab initio calculations.
The Heats of Formation at 25° of the Crystalline Hydrides and Deuterides and Aqueous Hydroxides of Lithium, Sodium and Potassium<sup>1</sup>
Nascent rotational quantum state distribution of NaH (NaD) from the reaction of Na*(4 <sup>2</sup><i>P</i>) with H<sub>2</sub>, D<sub>2</sub>, and HD
作者:Solomon Bililign、P. D. Kleiber
DOI:10.1063/1.462507
日期:1992.1
The nascent rotational quantum state distributions of NaH and NaD products resulting from the reactions of Na*(4 2Pj) with H2, D2, and HD have been determined using the laser pump–probe technique. We have observed a bimodal rotational distribution with a minor component peaking at low J and a major component peaking at high J. We have observed no evidence for a kinematic isotope effect on the product distribution. Our results are consistent with a model wherein the reaction occurs predominantly on the attractive 2B2 potential energy surface in near C2v geometry with the rotational distribution being determined late in the exit channel.