Deflection, polarizability

Electrostatic deflection experiments have shown the acid-water adducts to be polar. However, larger clusters exhibit defocusing behavior indicative of a polarizable, but essentially nonpolar, species. Only for the pure acetic acid clusters, specifically the... 

The essential elements.of the experiment are a) an effusive molecular beam source, b) inhomogeneous deflecting electric polefaces, c) surface ionization detector, capable of translation in order to obtain the deflected beam pattern. 1, 2, are the distance from the source to the front of the polefaces, the length of the polefaces and the distance from the back of the polefaces to the detector, respectively. A general review of deflection methods for determining polarizabilities is given by Miller and Bederson (8). 

In fact, the situation with regards to the excited states of the monomers Is not much better. The first values for polar-zabllltles of some of the alkali halide dimers were reported at this Symposium by Bederson and co-workers (18). Experimental values of the polarizabilities of the monomers are not available and would be difficult to determine by deflection studies due to contributions resulting from the permanent dipole moments. 

The deflection of clusters by an inhomogeneous magnetic field provides an indication of their magnetic susceptibility. Similar deflection in a static electric field has also been performed for alkali beams and is planned for the transition metals in order to obtain polarizabilities as a function of cluster size. 

The static polarizability of Sn clusters ( = 6-20) has been calculated using DFT and the B3P86 XC functional Agreement with experiment is good, provided the dipole moment of the cluster is taken into account. Indeed, in electric deflection experiment, the apparent polarizability of a rigid spherical rotor is the sum of the pure electronic contribution and of one due to the permanent dipole moment, 2/9 p /kBTrot, with Trot, the rotational temperature, which has been set to 3.5K in Ref. 101. 

Semiconductor cluster polarizabilities have been the subject of some very important experimental studies via beam-deflection techniques (Backer 1997 Schlecht et al. 1995 Schnell et al. 2003 Schafer et al. 1996 Kim et al. 2005) while they have been extensively studied using quantum chemical and density functional theory. In this research realm, one of the areas intensively discussed is the evolution of the cluster s polarizabilities per atom (PPA) with the cluster size. The PPA is obtained by dividing the mean polarizability of a given system by the number of its atoms. Such property offers a straightforward tool to compare the microscopic polarizability of a given cluster with the polarizability of the bulk (see O Fig. 20-16) as the latter is obtained by the hard sphere model with the bulk dielectric constant via the Clausius-Mossotti relation ... 

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