Observations of rotationally resolved C3 in translucent sight lines

The rotationally resolved spectrum of the A(1)Pi(u) <-- X-1Σ(+)(g) 000-000 transition of C-3, centered at 4051.6 Angstrom, has been observed along 10 translucent lines of sight. To interpret these spectra, a new method for the determination of column densities and analysis of excitation profiles involving the simulation and fitting of observed spectra has been developed. The populations of lower rotational levels (J less than or equal to 14) in C-3 are best fitted by thermal distributions that are consistent with the kinetic temperatures determined from the excitation profile of C-2. Just as in the case of C-2, higher rotational levels (J > 14) of C-3 show increased nonthermal population distributions in clouds that have been determined to have total gas densities below similar to 500 cm(-3).