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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.

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.

In this paper, thermal diffusion states of pure diethyl ether and its mixture with cellulose dinitrate tripolymer were uncovered by LAMMPS-based Molecular Dynamic (MD) simulations. Those MD simulations were generally performed through specified ReaxFF reactive force field to obtain the properties of the chemical system such as molecular energy, density, mean square displacement (MSD) and molecular coordinate. The result of MD simulations presented the clear superheating phenomenon of pure liquid diethyl ether system in the studied environment. The obtained phase transition point was much higher than the reported one. The deviation between two temperatures was about 132.369K. It was also demonstrated that the transition process was associated with the sharp increment of potential energy, volume, diffusion coefficient and cohesive energy. However, the split of these diethyl ether molecules was not uniform. The cluster-like transition state was observed before the end of the vaporing process (460K). As for the addition of cellulose dinitrate tripolymer, these molecules were not agglomerated in the simulated organic mixture. However, the diffusion of cellulose dinitrate tripolymer was much weaker than those diethyl ether molecules. While the concentration of cellulose dinitrate tripolymer was higher, molecular interactions of this organic mixture were consequently improved, and this further limited the diffusion behavior of the entire chemical system. It could be concluded that the diffusion behavior of the entire organic system was decreased with more amount of cellulose dinitrate tripolymer molecules.

Some people think that carbon and sustainable development are not compatible. This textbook shows that carbon dioxide (CO₂) from the air and bio-carbon from biomass are our best allies in the energy transition, towards greater sustainability. We pose the problem of the decarbonation (or decarbonization) of our economy by looking at ways to reduce our dependence on fossil carbon (coal, petroleum, natural gas, bitumen, carbonaceous shales, lignite, peat). The urgent goal is to curb the exponential increase in the concentration of carbon dioxide in the atmosphere and hydrosphere (Figures 1.1 and 1.2) that is directly related to our consumption of fossil carbon for our energy and materials The goal of the Paris agreement (United Nations COP 21, Dec. 12, 2015) of limiting the temperature increase to 1.5 degrees (compared to the pre-industrial era, before 1800) is becoming increasingly unattainable (Intergovermental Panel on Climate Change (IPCC), report of Aug. 6, 2021). On Aug. 9, 2021 Boris Johnson, prime minister of the United Kingdom, declared that coal needs to be consigned to history to limit global warming. CO₂ has an important social cost…