Studies on gas-surface dynamics have acquired considerable importance recently not only for their intrinsic scientific interest but also for their technological potential. This article first briefly describes various experimental techniques and a number of interesting recent observations resulting from these techniques. It then discusses certain important theoretical methodologies being extensively used nowadays. There arethree broad overlapping streams of theoretical works, viz classical, semi-classical and quantum-mechanical. There are alsothree basic problems in gas-surface interaction, viz (i) the interface presents a manybody problem; (ii) the solid surface is “rough”; (iii) the number of diffractive and inelastic channels is enormously large. The semi-classical approaches appear to dominate over the others in variety and quantity. But the sources of benchmark theoretical results are still the rigorous classical-trajectory and close-coupling quantum-mechanical calculations. The coming years are likely to witness not only increased numerical accuracy through refinements in semi-classical and quantum-mechanical approaches, but also certain special approximate methods designed to yield deeper physical insights into the nature of gas-surface interaction.

A simple model for the adsorption of gas molecules on fractal surfaces is formulated. For surface reactions where adsorption is the rate determining step, considerations based on the probability of adsorption are sufficient to describe the kinetics. Different values of fractal dimension correspond to different values of rate constant for adsorption. A linear relationship between the dynamics and the geometric properties of a solid surface as well as a statistical mechanical relationship between internal partition functions of the gas molecule and the adsorption complex are obtained.

In the present investigations, attempts were made to grow semi-organic composition of thiourea mixed with dysprosium chloride (abbreviated as TuDyCl). The growth of this semi-organic composition is being achieved by room-temperature slow evaporation technique. These were then characterised by using techniques like powder X-ray diffraction, scanning electron microscope (SEM), UV–Vis analysis, Fourier transformation infrared spectroscopy (FTIR), thermal and electrical studies. The composition crystallises in an orthorhombiccrystal system having the space group P$_{nma}$. The crystallinity and purity were tested by powder X-ray diffraction. Structural morphology, as analysed using SEM, suggests the formation of microcrystals with certain inclusions. Optical spectra suggest a good optical transmission in the entire visible region and the lower cut-off wavelength at 278 nm. The absence of absorption of light in the visible region makes the crystals suitable for optoelectronic applications. The band gap comes out to be 4.24 eV. Other parameters like extinction coefficient, refractive index,optical and electrical conductivity were also analysed. Identification of the expected functional groups and various modes of vibrations present in the grown crystals was carried out by FTIR. Thermal effects, such as dehydration,melting and decomposition mechanism, were observed using thermoanalysis techniques. Electrical performance was tested to understand the electrical response of the materials with externally applied fields as a function of temperature and frequency.