Full-dimensional quantum calculations of vibrational energy levels of acetylene (HCCH) up to 13,000 cm−1

We report full-dimensional converged quantum mechanical calculations of highly excited vibrational (J=0) energy levels of acetylene (HCCH) up to 13,000 cm−1 above the zero-point-energy level. The calculations were carried out using the Lanczos algorithm and a mixed basis/grid representation for the six-dimensional wavefunction. Both the parity and diatomic exchange symmetry were adapted in the calculation. Results on two potential energy surfaces were obtained and compared with both experimental and previous theoretical results.