Influence Of Rotational Relaxation Research Articles

Synchrotron-radiation-based perturbed angular correlations used in the investigation of rotational dynamics in soft matter

A new method, synchrotron-radiation-based perturbed angular correlations, was applied to study rotational dynamics of M\"ossbauer atoms in soft condensed matter, using incoherent nuclear resonant scattering of synchrotron radiation. A theory was developed that describes the correlations for the scattering by an ensemble of randomly oriented spins under the influence of rotational relaxation. In a feasibility study a molecular glass former doped by probe molecules was investigated above the glass transition up to the normal liquid state. A comparison of the obtained rotational relaxation rates with data from dielectric spectroscopy shows that the probe molecules reproduce the dynamics of the glass former.

The influence of rotational and vibrational energy relaxation on boundary-layer stability

We investigate the influence of rotational and vibrational energy relaxation on the stability of laminar boundary layers in supersonic flows by numerically solving the linearized equations of motion for a flow in thermal non-equilibrium. We model air as a mixture of nitrogen, oxygen and carbon dioxide, and derive accurate models for the relaxation rates from published experimental data in the field of physical chemistry. The influence of rotational relaxation is to dampen high-frequency instabilities, consistent with the well known damping effect of rotational relaxation on acoustical waves. The influence of rotational relaxation can be modelled with acceptable accuracy through the use of the bulk-viscosity approximation when the bulk viscosity is computed with a formula described herein. Vibrational relaxation affects the growth of disturbances by changing the characteristics of the laminar mean flow. The influence is strongest when the flow field contains a region at, or near, stagnation conditions, followed by a rapid expansion, such as inside wind tunnels and around bodies with a blunt leading edge, whereby the rapid expansion causes the internal energy to freeze in a distribution out of equilibrium. For flows at Mach 4.5 and stagnation temperature of 1000 K, the total amplification exhibited by boundary-layer disturbances over a sharp flat plate in wind-tunnel flows can reach a value that is fifty times as high as the value computed under the assumption of thermal equilibrium. The difference in amplification can be twice as high in the case of a blunt flat plate at atmospheric flight conditions.

The influence of rotational relaxation on the unresolved Q-branch density-shift induced by vibrational dephasing

The density dependence of the contributions of elastic vibrational dephasing and rotationally inelastic collisions into the overall shift of the Raman Q-branch profile of nitrogen has been theoretically studied. The results have been found to accurately reproduce the frequency shift measurements over a wide density range (10–900 amagat), also including the liquid phase.

Analysis of the characteristics of a pulsed chemical DF-CO2laser under lasing and amplification conditions

Experimental and calculated data are used in an analysis of the characteristics of a pulsed chemical DF–CO2 laser under free-running and amplification regimes. A deviation of the distribution of the populations of the vibrational states of the CO2 molecule from the Boltzmann law was observed in the course of amplification of a saturating 150-nsec pulse. The role of a hot R 23 (0111–1110) transition and the influence of rotational relaxation on the kinetics of lasing of individual vibrational–rotational lines, on the output radiation pulse profile, and on the output energy were considered. The calculated and experimental values of the unsaturated gain and of the output energy in the free-running regime were in good agreement when the degree of initiation (dissociation) was far from the lasing threshold.

Influence of rotational relaxation on multiphoton dissociation of CF3Br in the presence of buffer gases

A study was made of multiphoton dissociation of the CF3Br molecule in the presence of various buffer gases (He, Ne, N2, Ar, Kr). The main mechanism of the influence of collisions on the dissociation process at low buffer gas pressures (pb < 100 Torr) was found to be rotational relaxation.

Influence of rotational relaxation in a CO2amplifier on the shape of a short amplified pulse

An investigation was made into the change in shape of a nanosecond radiation pulse as it propagated in a TEA CO2 amplifier having a 5-m long amplifying medium. It was shown experimentally and theoretically that under certain conditions there was a substantial change in the pulse shape; a second peak caused by rotational relaxation in the amplifying medium appeared at the trailing edge of a pulse.

Influence of Rotational Relaxation on Tropospheric OH Laser Induced Fluorescence Measurements

Abstract Rotational relaxation of OH molecules in the 2II electronic ground state has been observed to occur in collisions with water molecules with gas kinetic probability. It causes an additional contribution to the already well known sources of interference when LIF is used to monitor tropospheric OH. As the laser generated OH is originally produced mostly in high rotational states, the fast relaxation phenomenon leads to a further population of OH in low rotational states. These states are used to monitor tropospheric OH by spectroscopic methods. The observed effect therefore increases the interference. A mathematical analysis is presented, revealing the effect of all relevant parameters.

Rotational relaxation of nitrogen in a viscous shock layer at low reynolds numbers

The viscous shock-layer model is used to examine relaxation of rotational degrees of freedom of molecular nitrogen in flow of a rarefied gas near the stagnation flow line around a sphere. It is shown that in the strongly smeared shock-wave region the rotational degrees of freedom can exhibit substantial nonequilibrium, leading to the increase of temperature and an increase of shock-layer thickness as compared with the equilibrium values. The influence of rotational relaxation on the shock-wave structure is discussed, and boundaries are found for the flow regions when rotational relaxation plays on important role,A comparison is made between the results of numerical calculations and experimentally obtained density profiles available in the literature near the stagnation line in flow of a rarefied gas over a sphere [1, 2]. Quite good agreement is obtained between the results of the calculation and experimental data over a wide range of Reynolds numbers.