Search

We report experiments on the internal state distribution and angular momentum alignment in an expanding jet of Na2 molecules seeded in Ar. The results show that even at a distance of one nozzle diameter from the nozzle exit, the distribution function is already far from equilibrium. It is found that the deviation from equilibrium can be expressed in a polynomial in the total internal energy of the molecules. This result is very analogous to the outcome of a first order Chapman–Enskog treatment for molecules with internal states. The transition to molecular flow marks the breakdown of the simple relationship mentioned above. This points to the fact that data taken far away from the nozzle are by themselves of limited value for a test of calculated distributions starting from nozzle conditions. Further we present measurements of alignment for two rovibrational states of Na2 molecules. Far downstream the nozzle the results are in agreement with previous experiments in molecular beams. In the vicinity of the nozzle reorienting collisions of excited-state molecules play an important role. It appears that these collisions strongly depend on the rotational state of the molecules: the cross sections are inversely proportional to J’2. [ABSTRACT FROM AUTHOR]

We show that by means of a linear transformation of the trial functions in the second approximation to the distribution function, a simple expression for the thermal conductivity of polyatomic molecules can be obtained. This is made possible using our results of state-selective measurements of the nonequilibrium distribution in a heat conducting gas. Also a direct relationship between the pure gas transport coefficients can be deduced, which gives an accurate description of both monatomic and polyatomic gases. This is illustrated by a comparison between calculated and experimental data of the thermal conductivity. [ABSTRACT FROM AUTHOR]

A technique is presented with which the alignment of molecular angular momenta in molecular beam scattering can be measured. In principle the method can be applied to any molecule as long as the polarization of an absorbed or emitted photon is related directly to the orientation of the molecular angular momentum and as long as the orientation of the molecular angular momentum can be rotated by precession in a magnetic field. The main advantage of the method is that the relative change in fluorescence intensity, as modulated by the magnetic field, is directly proportional to the alignment of the angular momenta. Both magnitude of the alignment and direction of the principal axis of the orientational distribution of the angular momenta can be determined from the field dependence of the fluorescence intensity. The applicability of the method is demonstrated with some experimental results in which the alignment of Na2 is determined after scattering by He. [ABSTRACT FROM AUTHOR]

Measurements of angular momentum alignment in molecular beam scattering are presented for scattering of Na2 by He, Ne, and Ar. A mechanism for the production of this alignment is discussed, based on mJ conservation for quantization along the momentum transfer vector. The experimental results differ in several aspects from the predictions of this simple mechanism. It is found that the differential cross sections are strongly dependent on mJ. Furthermore, it is found that the principal axis of the orientational distribution does not coincide with the momentum transfer vector. The discrepancy is attributed to a nonstrict mJ conservation in the collision. These experiments are therefore expected to provide a sensitive probe to the nonsudden aspects of molecular scattering. [ABSTRACT FROM AUTHOR]