Theoretical Study On Doped Carbon Clusters C_nS^2-(n=6-18), C_nAl₂⁺(n=1-8) And HC_nSi⁺(n=1-10)

The dissertation was devoted to the theoretical study on S-doped carbon cluster dianions C_S^2-(n = 6-18), Al-doped carbon cluster cations C_nAl₂⁺ (n = 1-8), H- and Si-doped carbon cluster cations HC_nSi⁺ (n = 1-10). All possible models were explored employing B3LYP combining Molecular Graphics and Molecular Mechanics. Geometry optimization and calculation of vibrational frequencies were conducted by means of B3LYP/6-311G^*( B3LYP/6-311G^**) method. To ascertain the ground-state structures, the single point energies were calculated at the B3LYP/6-311+G* (B3LYP/6-311+G^**) level. Based on NBO charge calculations and the analyses of valence-bond structures, we summarized the structural rules of clusters. The trend of odd-even alternation was interpreted according to the variation of bonding character, electronic configuration, electron detachment energy, incremental binding energy and energy difference. Knowledge acquired in this dissertation can provide helpful information for further theoretical studies.Main results and conclusions were summarized as follows:1.C_NS^2-(N = 6-18)The most probable ground-state isomers of C_nS^2- (n = 6-18) are linear with the sulfur atom located at one end of the C_n chain. When n is even, the isomer is polyacetlylene-like. The C_nS^2- (n = 6-18) with even number of carbon atoms are more shtable than those with odd numbrer, mathching the peak pattern observed in studies of mass spectrometry. The trend of odd-even alternation is also detected in certain bond length, atomic charge, electronic configuration, the highest vibrational frequency, energy difference, electron detachment energy, and incremental binding energy of the most probable ground-state isomers.2.C_nAl₂⁺(n=1-8)The most probable ground-state structures of C_nAl₂⁺ (n = 1-8) are linear with the aluminum atoms located at each end of C_n chain. There is a geometrical mutation from linear structrue to bent linear structrue when n = 3-8. The C_nAl₂⁺ (n = 1-8) with even number of carbon atoms are more stable than those with odd numbrer. When n is even, the C_n chain is polyacetlylene-like, whereas for n is odd, the data suggest a cumulene-like arrangement. The calculated bond characters, incremental binding energy, vertical ionization potential and energy difference show the same odd-even pattern, which is consistent with the observed odd-even alternation of SIMS signal intensities.3.HC_Si⁺(n=1-10)The most probable ground-state isomers of HC_Si⁺(n=1-10)clusters are linear with the hydrogen and silicium atoms located at each end of the C_n chin. The HC_nSi⁺ (n = 1-10) with even number of carbon atoms are more stable than those with odd number. When n is even, the C_n chain is polyacetlyene-like.The calculated bond characters, atomic charge, electronic configuration, energy differernce, adiabatic ionization potential, incremental binding energy and the highest vibrational frequencies show the same odd-even pattern, which is consistent with the observed odd-even alternation in experimental studies.