Microwave spectral line widths of the transitionJ = 1 → 2 of OCS perturbed by non-polar perturbers,n-hexane, cyclohexane,n-heptane, carbon disulphide, carbon tetrachloride and benzene have been calculated using a recent theory of Mehrotra and Boggs.

The longitudinal relaxation timeT₁ and the transverse relaxation timeT₃ for the inversion levels of the NH₃ molecule have been calculated for NH₃ — NH₃, NH₃ — N₂ and NH₃ — H₂ collisions. The ratioT₂/T₁ lies between 1 and 2 which agrees well with the experiment. The phase shift effect onT₂ and on the collisioninduced line shift δω under the framework of the Mehrotra-Boggs theory have also been evaluated. The change in the line intensity ΔI/I, in four-level double resonance experiments was also calculated, and the significance of higher order interaction terms has been pointed out.

The theoretical calculation of line widths and line shifts for CO₂-Ar system is computed by the Mehrotra-Boggs theory. It is shown for this system that the phase shift effect is very important at large values of |m| wherem is the value of rotational quantum numberJ in the lower vibrational state. It is also pointed out that the Salesky-Korff theory is the same as the Mehrotra-Boggs theory.

When the collisional dynamics of two states under consideration for a radiative transition is different, the polarization and population relaxations in gas phase at low pressure are governed by four-, instead of three-, coupled Bloch-type equations. The general transient solutions of these four-coupled equations are solved by using the Laplace transformation technique. It has been found that an additional exponential term appears because of the effect. This is also responsible for the non-exponential character in the decay signal of a transient microwave pulse experiment, besides other factors reported earlier.

The dielectric relaxation studies of 4-ethylphenol-methanol mixtures have been carried out at various temperatures ranging from 10°C to 40°C using time domain reflectometry in the frequency range 10 MHz to 10 GHz. The relaxation mechanism in these systems is explained by Cole-Davidson model. The excess dielectric parameters, Kirkwood correlation factor and activation energy have been calculated and discussed with respect to molecular arrangements, and microdynamics of the binary mixture composed of both the associative type of liquids.

Time domain reflectometry method has been used in the frequency range of 10 MHz to 10 GHz to determine dielectric properties of aqueous solutions of acetonitrile in temperature range of 0°C to 40°C. The calibration method based on the least squares fit method has been used. The excess permittivity, activation energy, Kirkwood correlation factor and activation energy of acetonitrile-water system have also been determined. The dielectric data show that acetonitrile molecules interact such that the dipoles have a tendency to remain antiparallel.

Dielectric properties of nitriles have been studied using time domain reflectometry in the frequency range of 10 MHz to 10 GHz over the temperature range of 0°C to 45°C. The calculated dielectric relaxation parameters are compared with values for the corresponding n-alcohols. The dielectric behaviour in n-nitrile systems is quite different from the corresponding behaviour in n-alcohols. The dipoles in n-nitrile systems show a tendency to remain antiparallel, unlike in alcohol systems. The activation energy decreases with the increase of molecular size, whereas in hydrogen bonded liquid it increases.

The complex permittivity, static dielectric constant and relaxation time for tetrahydrofuran-water and acetone-water mixtures have been determined at 0°, 10°, 25° and 35°C using time domain reflectometry technique (TDR). The behaviour of relaxation time of the mixture shows a maxima for the mixture with 30% of water by volume. This suggests that the tendency to form cluster between water and solute molecule is maximum for this mixture. The excess permittivity for both tetrahydrofuran-water mixture and acetone-water mixtures, are found to be negative. The Kirkwood correlation factor has been determined at various concentrations of water. Static dielectric constant for the mixtures have been fitted well with the modified Bruggeman model. The values of the Bruggeman parametera for tetrahydrofuran is found to be more than the corresponding value for acetone.

The dielectric relaxation parameters, viz., static dielectric constant, ɛ, and relaxation times, τ, have been determined for chlorobenzene-methanol (CB-MET), 1,2 dichloro ethanemethanol (DE-MET) and dimethylene chloride-methanol (DC-MET) mixtures with thirteen different concentrations at three temperatures, viz., 15, 25 and 45°C. The experimental technique used for this work was the time domain reflectometry (TDR) in the frequency range of 10 MHz to 20 GHz using the Hewlett Packard HP 54750 sampling oscilloscope. The information regarding hydrogen bonding structural behavior in MET due to CB, DE and DC are obtained by using the theoretical models based on the excess properties. The data suggest that CB and DE are not influenced by hydrogen bonding in MET whereas DC is influenced by the hydrogen bonding mechanism in MET. It appears that the behavior of DC on MET is different from CB and DE in MET.