Oscillator strengths and radiative lifetimes for C2:: Swan, Ballik-Ramsay, Phillips, and d 3Πg←c 3Σu+ systems

High level ab initio calculations, using multireference configuration interaction (MRCI) techniques, have been carried out to investigate the spectroscopic properties of the singlet A (1)Pi(u)<- X (1)Sigma(+)(g) Phillips, the triplet d (3)Pi(g)<- a (3)Sigma(u) Swan, the b (3)Sigma(-)(g)<- a (3)Pi(u) Ballik-Ramsay, and the d (3)Pi(g)<- c (3)Sigma(+)(u) transitions of C-2. The MRCI expansions are based on full-valence complete active space self-consistent-field reference states and utilize the aug-cc-pV6Z basis set to resolve valence electron correlation. Core and core-valence correlations and scalar relativistic energy corrections were also incorporated in the computed potential energy surfaces. Nonadiabatic and spin-orbit effects were explored and found to be of negligible importance in the calculations. Harmonic frequencies and rotational constants are typically within 0.1% of experiment. The calculated radiative lifetimes compare very well with the available experimental data. Oscillator strengths are reported for all systems: f(v)(')v('), where 0 <= v <= 5. (c) 2007 American Institute of Physics.