High-level theoretical rovibrational spectroscopy beyond fc-CCSD(T): The C3 molecule

An accurate local (near-equilibrium) potential energy surface (PES) is reported for the C-3 molecule in its electronic ground state ((X) over tilde (1)Sigma(+)(g)). Special care has been taken in the convergence of the potential relative to high-order correlation effects, core-valence correlation, basis set size, and scalar relativity. Based on the aforementioned PES, several rovibrational states of all C-12 and C-13 substituted isotopologues have been investigated, and spectroscopic parameters based on term energies up to J = 30 have been calculated. Available experimental vibrational term energies are reproduced to better than 1 cm(-1) and rotational constants show relative errors of not more than 0.01%. The equilibrium bond length has been determined in a mixed experimental/theoretical approach to be 1.294 07(10) A in excellent agreement with the ab initio composite value of 1.293 97 A. Theoretical band intensities based on a newly developed electric dipole moment function also suggest that the infrared active (1,1(1),0) (0,0(0),0) combination band might be observable by high-resolution spectroscopy. (C) 2016 AIP Publishing LLC.