Structures and stabilities of CaC 3+ and CaC 3H + isomers

Abstract

A theoretical study of the CaC 3 + and CaC 3H + systems has been carried out. Predictions have been made for some of the molecular properties (geometries, dipole moments, and harmonic vibrational frequencies) which could help in their possible experimental detection. In addition, a topological analysis of the electron density and its associated Laplacian has also been carried out. The predicted global minimum for CaC 3 + is a rhombic four-membered ring 2d( 2A 1). Both doublet states of the other cyclic structure 3, 2B 2 and 2A 2, lie quite close in energy (about 4.0 and 9.6 kcal/mol, respectively, higher in energy at the G2(P) level). The linear isomer lies about 14.6 kcal/mol above the global minimum, at the G2(P) level. In the case of CaC 3H + the predicted global minimum is a bicyclic structure 2s( 1A 1). There are two isomers that lie close in energy: a linear species, 1t( 2Σ), and a four-membered ring, 3s( 1A 1); lie about 16.2 and 19.4 kcal/mol, respectively, at the G2(P) level, above the global minimum. Except in the case of linear isomer, protonation favours the singlet states over the triplet ones. Low ionization potential and high proton affinities are obtained for the most stable CaC 3 isomers. Therefore, if present in the interstellar medium, CaC 3 should be easily ionized and would react quite easily to give the protonated species.