THE MODEL OF LINEAR AGGREGATE OF AG COLLOIDAL PARTICLES WITH VARIABLEINTER-PARTICLE DISTANCES

A simplified method of calculation of the surface plasmon energy state s of the Ag colloidal aggregates characterized by varying inter-partic le (inter-sphere) distance has been developed. Ag colloidal aggregate is approximated by a linear (one-dimensional) assembly of N silver sph eres (of identical radii r and identical inter-sphere distances D) mut ually interacting by a dipole-dipole interaction. The calculations use the following parameters: N from I to 25, r = 2, 5 and 10 nm, D = 0, 0.5, 1 and 2 nm, water and/or vacuum embedding media. The perturbation energies V-min (stabilization energy) and V-max (destabilization ener gy) of the excited plasmon state of a linear aggregate of N spheres in teracting by the dipole-dipole interaction were calculated as the eige nvalues of perturbation matrix using the above-mentioned parameters. T he stabilization energy V-min increases with increasing number of sphe res in the aggregate and with increasing sphere radius, while it decre ases with increasing inter-particle (inter-sphere) distance. Calculati ons of the square values of the eigenvector coefficients show that the contribution of a particular single sphere to the total energy of the aggregate is the highest for the central sphere in the odd-N aggregat es and for the two central spheres in the even-N aggregates. The resul ts of the model calculations support the hypothesis that the differenc es between the surface plasmon absorption curves of the Ag colloid/mon omeric adsorbate and of the Ag colloid/polymeric (oligomeric) adsorbat e systems have their origin in the difference in the inter-particle di stance distributions.