Oscillator strengths and radiative lifetimes for C2: Swan, Ballik-Ramsay, Phillips, and dΠg3←cΣu+3 systems

Abstract

High level ab initio calculations, using multireference configuration interaction (MRCI) techniques, have been carried out to investigate the spectroscopic properties of the singlet A 1Piu<--X 1Sigmag+ Phillips, the triplet d 3Pig<--a 3Sigmau Swan, the b 3Sigmag-<--a 3Piu Ballik-Ramsay, and the d 3Pig<--c 3Sigmau+ transitions of C2. 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: fv'v", where 0<or=v<or=5.

C2emission features in the Red Rectangle

“…Einstein A coefficients for spontaneous emission have been obtained for a series of transitions using the calculated oscillator strengths by Kokkin et al (2007). The results for the Phillips and the Swan bands agree well with the coefficients calculated by van Dishoeck (1983) and Gredel et al (1989).…”

Another forbidden solar oxygen abundance: the [O I] 5577 Å line

“…The line list for the 0-1 and 1-2 bands of the C 2 Swan system was constructed in a similar way to the 0-0 band described in Meléndez & Cohen (2007), but with the line positions taken primarily from Tanabashi et al (2007) and complemented with Phillips & Davis (1968) data for the higher excitation lines not included by Tanahashi et al. Relative oscillator strengths for the 0-1 and 1-2 bands were taken from Kokkin et al (2007), normalizing those values to the laboratory oscillator strength of the 0-0 band recommended by Grevesse et al (1991), f 00 = 3.03 × 10 −2 . The rotational strengths were computed following Kovacs (1961) and the rotational dependence of the band strengths was taken into account (Dwivedi et al 1978).…”

Astronomical Molecular Spectroscopy

“…This sort of kinetic model had been built before by various groups [41]. However, there appeared to be some uncertainty in the transition moments of some of the band systems invoked in the models, which normally included the a with the experiment reporting 2085 cm À1 [42]. Such an agreement might have been satisfactory 20 years earlier, but since all other states agreed with the reported spectroscopy to within 0.1%, we were confident that the calculations for the c 3 S þ u state were indeed accurate, and searched the literature thoroughly.…”