  The aim of this work is to link the broad lambda 5450 diffuse interstellar
band (DIB) to a laboratory spectrum recorded through an expanding acetylene
plasma. Cavity ring-down direct absorption spectra and astronomical
observations of HD 183143 with the HERMES spectrograph on the Mercator
Telescope in La Palma and the McKellar spectrograph on the DAO 1.2 m Telescope
are compared. In the 543-547 nm region a broad band is measured with a band
maximum at 545 nm and FWHM of 1.03(0.1) nm coinciding with a well-known diffuse
interstellar band at lambda 5450 with FWHM of 0.953 nm. A coincidence is found
between the laboratory and the two independent observational studies obtained
at higher spectral resolution. This result is important, as a match between a
laboratory spectrum and a - potentially lifetime broadened - DIB is found. A
series of additional experiments has been performed in order to unambiguously
identify the laboratory carrier of this band. This has not been possible. The
laboratory results, however, restrict the carrier to a molecular transient,
consisting of carbon and hydrogen.

Instrumentation and Methods for Astrophysics;Astrophysics of Galaxies