Detection of Interstellar C_2 and C_3 in the Small Magellanic Cloud
  We report the detection of absorption from interstellar C_2 and C_3 toward
the moderately reddened star Sk 143, located in the near 'wing' region of the
SMC, in optical spectra obtained with the ESO VLT/UVES. These detections of C_2
(rotational levels J=0-8) and C_3 (J=0-12) absorption in the SMC are the first
beyond our Galaxy. The total abundances of C_2 and C_3 (relative to H_2) are
similar to those found in diffuse Galactic molecular clouds -- as previously
found for CH and CN -- despite the significantly lower average metallicity of
the SMC. Analysis of the rotational excitation of C_2 yields an estimated
kinetic temperature T_k ~ 25 K and a moderately high total hydrogen density n_H
~ 870 cm^-3 -- compared to the T_01 ~ 45 K and n_H ~ 85-300 cm^-3 obtained from
H_2. The populations of the lower rotational levels of C_3 are consistent with
an excitation temperature of about 34 K.
