Studies of Linear CnSe- (1 <= n <= 11) clusters produced from laser ablation: Collision-induced dissociation and ab initio calculations

Small carbon cluster anions doped with single selenium atom CnSe- (n = 1 to 11) were produced by laser ablating the mixture of selenium and carbon pow ders and were recorded by mass spectrometry. Distribution of the doped clus ter ions was found to vary with the mixed ratios of the sample, but only th e cluster with even number of carbon atoms could be produced in the experim ent. Experiment of collision-induced dissociation (CID) verified molecular formulas of the selenium polycarbon clusters and found that they tend to lo se a Se atom (for smaller size) or a CSe unit (for larger size). To examine the odd/even alternation effect and other structural features, the duster ions were further investigated by ab initio calculations with ROHF and B3LY P methods using 6-31G* basis set. Based on the studies of other CnX- cluste rs and statistical distribution of the CnSe- clusters, geometry of the clus ters was assumed to be linear chain with the selenium atom locating at its terminal and was fully optimized in the calculation. The calculated total e nergy, vertical electron detachment energy and fragmentation energy, bond l ength, and other structural parameters exhibit the alternation effect, show ing that CnSe- clusters with even n are more stable than the odd clusters, in a good consistency with the mass spectrometric observation. The structur al difference between opposite parties of CnSe- is found to reduce followin g the increasing number of carbon atoms. The theoretical investigation also shows that electron correlation has to be considered in the calculation an d the result obtained by the density function method is sufficient to descr ibe the structural features of CnSe- clusters. Besides, dissociation energi es of six dissociation channels, losing C, C-2, C-3. CSe, C2Se, or Se fragm ent, were calculated for CnSe- anions and the result also exhibits the pari ty effect and matches well with the CID experimental observation.