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In Figure 6 we plot P$_{k,}$$_{1}$/ (1 / 2 − χ$_{k}$ ) versus (1 / 2 − χ$_{k}$ ), which shows that the number of dipole-active eigenmodes increases with the number of particles in the cluster. According to (27) and (28), Figure 6 shows in fact the dielectric decrement versus its corresponding relaxation frequency for each dipole-active eigenmode of the given clusters. For clusters of two or three particles, there is one important active eigenmode close to 1 / 2, while for clusters of four particles there are two active eigenmodes. 

It can be conjectured that for a general linear cluster made of m particles, there are m − 1 eigenvalues close to 1 / 2, of which the largest one is always dipole-active and has the largest 

