The detection of cyanodiacetylene (HC5N) through observations of
multiple rotational transitions was spread through a number of reports across the span of
several years in a variety of interstellar objects. The initial 1976 report, by
Avery et al., found the 4-3 line
in Sgr B2 using the 46 m
telescope at Algonquin Radio Observatory in Canada.
Two more lines, 1-0 and 8-7, were reported later the same year by
Broten et al., also in Sgr B2 but
using the facility in Parkes, Australia.
In 1977, Little et al.
reported observing the 9-8 line in the Heiles2 dust cloud. The same line was subsequently observed by
Winnewisser & Walmsley in IRC +10216 in 1978.
A fifth line, for the 2-1 transition, was found in Sgr B2 and TMC-1 by
Gardner & Winnewisser and published in late 1978.
The 3-2 transition was observed by
Rodriguez & Chaisson in 1980, while
Jennings & Fox four consecutive transitions
(7-6, 8-7, 9-8, 10-9) in 1982.
Cyanodiacetylene (or cyanobutadiyne or 2,4-pentadiynenitrile) has two CC triple bonds,
making it the first member of the cyanopolyyne family. While species as large as HC11N have been
observed in space and HC17N in the lab, they are
very unstable and don't persist outside low pressure conditions.