Analysis of semiconductor cluster beam polarization taking small permanent dipole moments into account

Deflections of semiconductor cluster beams in an inhomogeneous electric field deliver enhanced polarizabilities for cold isolated GaNAsM clusters with odd number of atoms n = N + M up to n = 17. One speculated that the high polarizabilities result from their electronic open shell structure. This was qualitatively confirmed by optical absorption cross section measurements, but the enhancement of polarizability is too large to be explained through a Kramers-Kronig-relation as purely electronic effect. Moreover, quantum chemical calculations gave permanent dipole moments of some tenths of a Debye for certain compositions. The clusters are too heavy to identify, these dipole moments by beam broadening effects, but we will show in the present analytic investigation within classical top theory, that a slight reversible-adiabatic alignment of the clusters dipole moment in the electric field increases the average beam deflection and the derived polarizability values. This effect was up to now not taken into account and it offers a consistent explanation of the GaNAsM polarizabilities by small permanent dipole moments of some tenths of a Debye and a reasonable rotational temperature between 2 and 12 K.