Extending the Limits of Rotationally Resolved Absorption Spectroscopy: Pyrene

We report the rotationally resolved gas phase spectrum
of pyrene
(C16H10), which is now the largest molecule
to be observed with rotational resolution using absorption spectroscopy.
This represents a significant advance in the application of absorption
spectroscopy to large carbon-containing molecules of fundamental chemical
and astronomical importance. Such spectra will facilitate the search
for large and highly symmetric molecules in interstellar space, where
they may be abundant but cannot be detected without the support of
high-resolution laboratory spectra. Detailed assignment and analysis
of our spectrum indicates that pyrene is the most rigid rotor yet
observed, and that a supersonic expansion cools both the rotational
and vibrational temperatures of pyrene vapor produced in an oven source.