Core excitation-induced photodesorption of molecular and fragment ions from CO adsorbates on metal surfaces

Transport properties of a collisionless molecular gas between plane-parallel plates are influenced by a magnetic field because of precession of the molecules after polarization by surface collisions. A systematic analysis of phenomena of this kind is attempted by considering mass flow in two directions and heat flow in three directions, together with the five conjugate thermodynamic forces. For the case of diamagnetic linear rigid molecules, the phenomenological coefficients are expressed by matrix elements involving the surface scattering operator. Explicit expressions are derived for a simple model of that operator.

Transport phenomena in molecular Knudsen gas

Investigations of field effects upon transport phenomena in molecular gases have recently been extended from the hydrodynamic to trasition and Knudsen regimes. In the steady state of a binary mixture between parallel plates the average flow velocity, diffusive flux aand heat flux linearly depend upon small gradients of pressure, concentration and temperature. The relation is specified by a matrix of field- and pressure-dependent coefficients L αβ , each of which may be a tensor. The Onsager reciprocity, L αβ ( B )= L βα† (- B , is verified by a derivation from the linearized Boltzmann equation, by taking account of the symmetries of intermolecular and gas-surface collision operators. A more detailed analysis is possible at moderate rarefaction, when the fluxes can be split into bulk and boundary-layer parts, the latter involving field-dependent slip coefficients.

Onsager symmetries in field-dependent flows of rarefied molecular gases

The influence of rotational alignment on molecule–surface interaction is studied for CH3F and OCS colliding with a glass surface. Experiments were performed at 285 K with the technique of surface light‐induced drift using a flat channel, the alignment being produced through excitation by linearly polarized light. For molecules having rotational energy well below thermal, it is found that the accommodation coefficient for parallel momentum α, which can be related to the trapping/desorption probability, is larger if the angular momentum J is parallel to the surface (‘‘cartwheeling motion’’) than if perpendicular (‘‘helicopters’’). For CH3F the experiments indicate that this difference decreases strongly with increasing K, denoting the component of J along the principal molecular axis. Experiments on OCS confirm this behavior. For molecules having rotational energy well above thermal, however, the reverse behavior is found, viz., α is larger for helicopters than for cartwheels. This is consistent with molecu...

Role of rotational alignment in molecule–surface interaction for CH3F and OCS

Heat transfer—A review of the 1982 literature

The paper deals with the use of thermomagnetic effect in a Knudsen gas (i.e., the effect of the magnetic field on the heat flow between two surfaces) in studying nonspherical scattering of polyatomic molecules from a solid surface. The dependence of the effect on the field orientation has been experimentally investigated for the first time. As a result, it has become possible to establish the ranks of the tensors that determine the dependence of the scattering probability on the orientation of the angular momentum of a molecule. A new approach for constructing a theory of the effect has been proposed. This approach takes account of the arbitrary law of spherically symmetric scattering and examines the case of appreciable values of the nonsphericity parameters. From a comparison between the theoretical and experimental dependences of the heat flow on the field magnitude and orientation the expressions for the probability of inelastic nonspherical scattering of N 2 and CO molecules by gold and platinum surfaces have been obtained.

A study of the interaction between nonspherical molecules and a surface using the thermomagnetic effect in a Knudsen gas

On kinetic thermomagnetic phenomena in polyatomic Knudsen gases

The effect of a magnetic field on the Knudsen gas flow

The effect of a magnetic field, B, on heat flow in a gas in an intermediate pressure range has been studied. The ratio of the heat flow changes in the fields B ⊥ ▿T and B ‖ ▿T was found to change nonmonotonically with pressure in N2 and CO. With the decreasing pressure, a difference is observed between the dependence of heat flow on field orientation and the corresponding angular dependence in the limiting case Kn→0 ( Kn = l /L , l is the mean free path, L is the geometric size). An expression has been obtained for the heat flow in a magnetic field for Kn ≲ 0.1 from the solution of an integral kinetic equation. In particular, it has been shown that the special features of the Senftleben-Beenakker effect observed with the decreasing pressure arise not only due to spherically symmetric molecule-surface interaction, but also to nonspherical scattering on walls.

B.I. Nikolayev

Papers

A study of the interaction between nonspherical molecules and a surface using the thermomagnetic effect in a Knudsen gas

On kinetic thermomagnetic phenomena in polyatomic Knudsen gases

The effect of a magnetic field on the Knudsen gas flow

Effect of magnetic field on heat flow in a polyatomic gas in intermediate pressure range

On a model of gas-surface interaction for orientation dependent molecule-surface forces