Density functional theory study of C nF 3− ( n = 1–9) clusters

Abstract

In this paper, we report the design of numerous C n F 3 − ( n = 1–9) models. By means of B3LYP density functional method, we carried out geometry optimization and calculation on the vibrational frequency. After comparison of structure stability, we found that the structures of ground-state (G-S) isomers of odd- n C n F 3 − (i.e., n = 3, 5, 7 and 9) are with the three fluorine atoms located at one end of the linear C n chain. The G-S isomers of C 2F 3 −, C 4F 3 −, and C 8F 3 − are with two fluorine atoms bonded to an end carbon of the C n chain, and one fluorine atom bonded to the adjacent carbon atom. In other words, the two carbon atoms involved in bonding to the fluorine atoms are sp 2 hybridized and the C n chain is not linear. In the case of C 6F 3 −, the G-S isomer is planar cyclic in structure, with each of the three carbon atoms at one side of the hexagonal C 6 ring bonded to a fluorine atom. The C n chain of G-S C n F 3 − ( n = 3–9; C 6F 3 − being the exception) isomers are polyacetylene-like. It is found that the odd- n G-S C n F 3 − ( n = 1–9) are more stable than the adjacent even- n ones. The finding is in accord with the relative intensities of C n F 3 −observed in mass spectrometric studies. We provide explanations for such trend of even/odd alternation based on concepts of the geometrical structure, bonding character, atomic charges, vertical electron detachment energy, and incremental binding energy.