Theoretical study of low-lying states in phosphorus-containing carbon chains PC2nP

Abstract

Density functional theory has been used to explore the geometries and vibrational frequencies of the ground states for linear chains PC2nP (n=1-10). The vertical transition energies (E-T) for the 1(1)Sigma(u)(+) <- X(1)Sigma(g)(+) transition in PC2nP have been studied by time-dependent density functional theory and CASPT2 method. Based on the present calculations, the explicit exponential expression for the size dependence of E-T in linear carbon chains has been suggested. The complete active space self-consistent field approach has been employed to locate both the ground state and the selected excited states of PC2nP (n= 1-5) for structure comparison. Theoretical investigations on relevant excited states reveal that distinct non-linear spectroscopic feature in such polyynes can be ascribed to difference in bonding between the ground and excited states. At the B3LYP/6-311 +G* level, the first adiabatic and vertical ionization energies have been calculated. The dependence relationship between the ionization energies (IE) and the size in linear PC2nP is obtained. E-T and IE of PC2nP are compared with those of linear NC2nN and pure carbon chains CC2nC, and they are explained reasonably. (c) 2005 Elsevier B.V. All rights reserved.