The Senftleben–Beenakker effect is the dependence on a magnetic or electric field of transport properties (such as

viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...

and

heat conductivity The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal ...

) of polyatomic gases. The effect is caused by the

precession Precession is a change in the orientation of the rotational axis of a rotating body. In an appropriate reference frame it can be defined as a change in the first Euler angle, whereas the third Euler angle defines the rotation itself. In othe ...

of the (magnetic or electric)

dipole In physics, a dipole () is an electromagnetic phenomenon which occurs in two ways: *An electric dipole deals with the separation of the positive and negative electric charges found in any electromagnetic system. A simple example of this system i ...

of the gas molecules between collisions. The resulting rotation of the molecule averages out the nonspherical part of the collision

cross-section Cross section may refer to: * Cross section (geometry) ** Cross-sectional views in architecture & engineering 3D *Cross section (geology) * Cross section (electronics) * Radar cross section, measure of detectability * Cross section (physics) **Ab ...

, if the field is large enough that the precession time is short compared to the time between collisions (this requires a very dilute gas). The change in the collision cross-section, in turn, can be measured as a change in the transport properties. The magnetic field dependence of the transport properties can also include a transverse component; for example, a heat flow perpendicular to both temperature gradient and magnetic field. This is the molecular analogue of the

Hall effect The Hall effect is the production of a voltage difference (the Hall voltage) across an electrical conductor that is transverse to an electric current in the conductor and to an applied magnetic field perpendicular to the current. It was disco ...

and

Righi–Leduc effect In solid-state physics, the thermal Hall effect, also known as the Righi–Leduc effect, named after independent co-discoverers Augusto Righi and Sylvestre Anatole Leduc, is the thermal analog of the Hall effect. Given a thermal gradient across a so ...

for electrons. A key difference is that the gas molecules are neutral, unlike the electrons, so the magnetic field exerts no

Lorentz force In physics (specifically in electromagnetism) the Lorentz force (or electromagnetic force) is the combination of electric and magnetic force on a point charge due to electromagnetic fields. A particle of charge moving with a velocity in an elect ...

. An analogous magnetotransverse heat conductivity has been discovered for

photons A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they alway ...

and

phonons In physics, a phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, specifically in solids and some liquids. A type of quasiparticle, a phonon is an excited state in the quantum mechanical ...

. The Senftleben–Beenakker effect owes its name to the physicists

Hermann Senftleben Hermann Senftleben (April 8, 1890, in Bremen – 1975 in Recklinghausen) was a German physicist and physical chemist. Education and life Senftleben was born in Bremen. After graduating from the König-Wilhelm-Gymnasium in Breslau, Senftleben ...

(Münster University, Germany) and

Jan Beenakker Joannes Joseph Maria Beenakker (February 1, 1926, in Koog aan de Zaan – July 23, 1998, in Leiden), more often known as Jan J. M. Beenakker or Jan Beenakker, was a Dutch physicist and the rector of the Leiden University. Education and career B ...

(Leiden University, The Netherlands), who discovered it, respectively, for

paramagnetic Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, d ...

gases (such as NO and O₂) and

diamagnetic Diamagnetic materials are repelled by a magnetic field; an applied magnetic field creates an induced magnetic field in them in the opposite direction, causing a repulsive force. In contrast, paramagnetic and ferromagnetic materials are attracted ...

gases (such as N₂ and CO). The change in the transport properties is smaller in a diamagnetic gas, because the magnetic moment is not intrinsic (as it is in a paramagnetic gas), but induced by the rotation of a nonspherical molecule. The importance of the effect is that it provides information on the angular dependence of the intermolecular potential. The theory to extract that information from transport measurements is based on the Waldmann–Snider equation (a quantum mechanical version of the

Boltzmann equation The Boltzmann equation or Boltzmann transport equation (BTE) describes the statistical behaviour of a thermodynamic system not in a state of equilibrium, devised by Ludwig Boltzmann in 1872.Encyclopaedia of Physics (2nd Edition), R. G. Lerne ...

for gases with rotating molecules). The entire field is reviewed in a two-volume monograph.Frederick R. W. McCourt, Jan J. M. Beenakker, Walter E. Köhler, and Ivan Kuščer, ''Nonequilibrium Phenomena in Polyatomic Gases'' (Oxford University Press, 1991).

References

External links

Historical remarks
on the experiment by Jan J. M. Beenakker.
Historical remarks
on the theory by Siegfried Hess (a student of Ludwig Waldmann). {{DEFAULTSORT:Senftleben-Beenakker effect Gases

See also

References

External links