SIMBAD references

The recent assignment of two broad diffuse interstellar bands (DIBs) near 4882 and 5450 Å to the propadienylidene (l-C₃H₂) molecule is examined using a statistically meaningful sample of targets. Our spectra clearly show that the strength ratio of two broad DIBs is strongly variable, contrary to what should be observed if both features are due to l-C₃H₂, since the proposed transitions are lifetime broadened and start from the same level. Moreover, even in directions where the 4882 DIB and 5450 DIB are strong, the third expected l-C₃H₂band, in the 5165-5185 Å region, is absent. Another puzzling characteristic of l-C₃H₂ as the proposed carrier of both broad diffuse bands is its column density of several 10¹⁴/cm2, inferred from the equivalent width of the 5450 DIB. This value is one order of magnitude higher than N(CH) toward the same objects and two to three orders of magnitude higher than N(H₂CCC), measured at radio frequencies in absorption, for comparable samples of the diffuse medium. We conclude that the proposed identification of broad DIBs is unjustified.