On the geometrical structure of the C+3 cation—an a b i n i t i o study

Abstract

The potential energy surface of the C+3 cation has been investigated using coupled cluster techniques and large basis sets. The results are particularly sensitive towards the level of electron correlation. Spin contamination even produces a ‘‘false stationary point’’ at the UHF/6-31G* level. C+3 has a cyclic 2B2 ground state with predicted geometry r=1.3242 Å, θ=73.06° (MP2/6-311G*, empirically corrected bond distance). At the highest level of theory considered, the linear structure (2Σ+u state) lies about 2 kcal/mol above the ground state: this might imply quasilinearity. There is also a low barrier towards degenerate isomerization: at high temperatures, C+3 will be extremely floppy. Harmonic frequencies (UHF/6-31G*) as well as double-harmonic IR and Raman intensities are given for various structures of C+3. Interesting analogies of C+3 with B3 and B2N are pointed out. The heat of formation at 298.15 K, vertical and adiabatic ionization potentials of C3 are predicted as 194.9±2 kcal/mol, 11.92±0.1 eV, and 11.84±0.1 eV, respectively.