Selenium clusters are doped with sodium atoms in the reaction zone of a dual laser vaporization source. Product clusters Se-N and Na2SeN with N = 4-8 are deposited in a nitrogen matrix and investigated by Raman spectroscopy. Beside the Raman band of pure SeN clusters, a new intense band between 165 and 225 cm(-1) is observed. Within a simple model of dynamical charge transfer the new band is attributed to certain vibrational modes with considerable changes of Na-Se bond lengths. The assignment is confirmed by density functional calculations. A bonding model for the Na2SeN clusters containing horseshoe shaped polyanionic selenium chains is developed. (C) 2004 Elsevier B.V. All rights reserved.