The interstellar $\mathsf{{\vec C}_3}$ chain molecule in different interstellar environments

Abstract

Abstract.We present an analysis of spectra of six stars taken with high resolution (R = 220 000). The stars are reddened by molecular clouds that differ by the relative strength of the 5797 and 5780 diffuse interstellar bands (DIBs). The high signal-to-noise ratio of the spectra (S /N ≈ 700-1000) shows that the abundance of the linear molecule C 3 with respect to E B−V varies considerably from one star to an other. There is no correlation with E B−V . The strong variations in the abundance of C 3 must therefore be caused by another circumstance. We point out that this may be the case: from an analysis of the interstellar potassium lines in the same spectra we conclude large differences in the state of ionization produced by interstellar photons with energies below the ionization potential of hydrogen. The ratio of the abundances of C 3 and C 2 varies considerably in different directions, even when the ratio between the strengths of various DIBs remains approximately constant.

Rovibrational energy transfer in the He-C3 collision: Potential energy surface and bound states

“…In the dense ISM the presence of C 3 was proven using its mid-and far-infrared vibrational transitions. 7, 9, 11 C 3 was also identified in the diffuse interstellar medium, first by Maier et al 8 and later in several other studies 12,13 along different lines of sight.…”

The 4051-Å band of C3 (ÃΠu1−X̃Σg+1, 000-000): Perturbed low-J lines and lifetime measurements

“…2 The identity of the carrier as C 3 was proved unambiguously by the 13 C isotope work of Douglas, 3 and later rotational analyses by Gausset et al 4,5 showed that the bands represent a 1 ⌸ u − 1 ⌺ g + transition of a linear molecule, where the lower state is the ground state. 2,[10][11][12][13] One of the interesting features of these spectra 2 is that the R͑0͒ line of the 000-000 band at 4051 Å was "uniformly underpopulated relative to what was expected from a thermal distribution that fitted J = 2-10." For example, the ground state has an unusually low bending frequency of 63.416 529͑40͒ cm −1 , 6,7 which, as discussed by Walsh, 8 is a result of its having no g electrons to provide a "backbone."…”

Observations of Rotationally Resolved C3in Translucent Sight Lines

“…Roueff et al (2002) applied their sophisticated C 3 excitation model to all three of the detections by Maier et al (2001)-Oph, Per, and 20 Aql-along with their own observations of HD 210121, but none of the observations determined the population of C 3 in J > 14 well enough to constrain the full excitation model. Galazutdinov et al (2002) have since provided spectra of C 3 toward Oph and HD 152236, without analysis of the excitation.…”