Narrow Results

A survey of recent Raman scattering studies on the interstitial hydrogen molecule (H₂) in Si and GaAs is presented. It is shown that properties of H₂ strongly depend on the nuclear spin state I. In either material, para-H₂ (I=0) is unstable against irradiation with band gap light. In the case of Si, para-H₂ also preferentially disappears from the Raman spectra in the course of storage at room temperature in the dark. Possible explanations for this surprising behavior are discussed and compared with the latest infrared absorption studies.

The theoretical calculation of the refractive indices is of great significance for the developments of new optical materials. The calculation method of refractive index, which was deduced from the electron-cloud-conductor model, contains the shape and direction factor $〈g〉$. $〈g〉$ affects the electromagnetic-induction energy absorbed by the electron clouds, thereby influencing the refractive indices. It is not yet known how to calculate $〈g〉$ value of non-spherical electron clouds. In this paper, $〈g〉$ value is derived by imaginatively dividing the electron cloud into numerous little volume elements and then regrouping them. This paper proves that $〈g〉=2/3$ when molecules’ spatial orientations distribute randomly. The calculations of the refractive indices of several substances validate this equation. This result will help to promote the application of the calculation method of refractive index.

We are interested in dynamics of a system in an environment, or an open system. Such phenomena as crossover from Markovian to non-Markovian relaxation and thermal equilibration are of our interest. Open systems have experimentally been studied with ultra cold atoms, ions in traps, optics, and cold electric circuits because well-isolated systems can be prepared here and thus the effects of environments can be controlled. We point out that some molecules solved in isotropic liquid are well isolated and thus they can also be employed for studying open systems in Nuclear Magnetic Resonance (NMR) experiments. First, we provide a short review on related phenomena of open systems that helps readers to understand our motivation. We, then, present two experiments as examples of our approach with molecules in isotropic liquids. Crossover from Markovian to non-Markovian relaxation was realized in one NMR experiment, while relaxation-like phenomena were observed in approximately isolated systems in the other.

This paper focuses on the use and value of XPS and NEXAFS spectroscopies to unveil the nature of the chemical bond of various bifunctional nitrile molecules adsorbed on Si(001) 2×1 at 300 K. The adsorption modes are also discussed in the light of recent theoretical publications devoted to optimized geometries and reaction paths of these molecules on Si(001).

The newly observed exotic mesons above threshold were widely discussed in the molecular picture. To understand deeper their structures, we here discuss the spin () of a heavy quark-antiquark pair in an S-wave meson-antimeson system by constructing explicitly the spin wave function. One finds two selection rules for (a) the total angular momentum J is larger than the maximum angular momentum of the light degree of freedom or smaller than the minimum one; (b) J^C = 1⁺, 2^-, 3⁺, ⋯ if the two mesons are different but belong to the same doublet. This feature may be used to constrain possible strong decay channels.

The molecular approach of a spin model is constructed on the Bethe lattice (BL), and then it is examined in terms of exact recursion relations. Rather than assuming that each BL site is inhabited by a single spin, each site is occupied by two spin-1/2 atoms A and B, forming a molecule. Each molecule is considered to contain two spin-1/2 atoms, as well as $q=3,4,$ or 6 nearest-neighbor molecules. In addition to the internal interactions between the atoms of each molecule, the molecules interact via their atoms in terms of bilinear interaction parameters J. Atoms of a molecule interact with $J_{A^i{B}^i}$, while the molecules interact via their atoms in terms of $J_{A^i{B}^{i+1}}=J_{B^i{A}^{i+1}}$ and $J_{A^i{A}^{i+1}}=J_{B^i{B}^{i+1}}$. After obtaining the magnetizations of each atom in the central molecule of the BL, the average magnetization of the molecule is determined. It is found that the model presents first-and second-order and random phase transitions. The model also displays tricritical, bicritical and end points, in addition to reentrant behavior for appropriate J values.