The pure carbon chain molecule pentatetraenediylidene, C5,
has been detected in the circumstellar envelope of the famous carbon star
CW Leo, aka IRC +10216, by
P. F. Bernath, K. H. Hinkle, and J. J. Keady,
Detection of C5 in the Circumstellar Shell of IRC +10216,
Science 244, 562564 (1989)
before it was actually detected in the laboratory. 16 P and R branch transitions of the ν3 band were detected around 2169 cm1 of which 13 appear to be unblended.