Transition probabilities and radiative lifetimes of C2- : A high level theoretical investigation

Dicarbon species are of particular interest within the physical chemistry community. However, contrary to neutral C-2, the theory of electronic structure and spectra concerning C-2(-) ions is not well-established. To address this gap in information, high-level multireference configuration interaction (MRCI) calculations have been performed, and new potential energy curves for fourteen low-lying states of C-2(-) are reported. The best estimate for the ground dissociation energy is 64,720 cm(-1) at the MRCI+Q/AV5Z level of theory. The first excited state, A(2)Pi(u), lies at 3,836 cm(-1) (R-e = 2.4829 a(0) and omega(e) = 1649 cm(-1)). The infrared A(2)Pi(u) - X-2 Sigma(+)(g) transition has Einstein coefficients of the order of 10(3)-10(4) s(-1). The lifetime of the A(2)Pi(u) state is given in microseconds. For the B-2 Sigma(+)(u) state, it was calculated tau(0) approximate to 78 ns in good accord with the experimental value of 77 +/- 8 ns. The a(4)Sigma(+)(u) state is placed at an excitation energy of 32,369 cm(-1), much higher than expected by experimentalists (19,448 cm(-1)). The spin-forbidden transitions a(4)Sigma(+)(u) - X-2 Sigma(+)(g) are strong enough to be detected experimentally (A(04) approximate to 3 x 10(6) s(-1)). The 1(4)Pi(g) - a(4)Sigma(+)(u) transitions are more concentrated in the IR region. The radiative lifetime of 1(4)Pi(g) is computed to be 12 mu s. There is no doubt that the current data considerably enhance our understanding of the spectroscopy of C-2(-).