Cyano-Polycyclic Aromatic Hydrocarbon Interstellar Candidates: Laboratory Identification, Equilibrium Structure and Astronomical Search of Cyanobiphenylene

The interplay between laboratory rotational spectroscopy
and radio
astronomical observations provides the most effective procedure for
identifying molecules in the interstellar medium (ISM). Following
the recent interstellar detections of several Polycyclic Aromatic
Hydrocarbons (PAHs) and cyano derivatives in the dense molecular cloud
TMC-1, it is reasonable to consider searching for other cyano-PAHs
in this astronomical source. We present a rotational spectroscopy
investigation of the two cyano derivatives of the PAH biphenylene,
a plausible reaction product of interstellar benzyne. The rotational
spectrum provided molecular parameters for the parent species and
14 monosubstituted isotopologues for each isomer. An accurate equilibrium
structure was determined for both isomers using Watson’s mass-dependence
method (rm(2)), offering information
on its uncommon ring union. Astronomical searches for the cyanobiphenylene
isomers have been undertaken in TMC-1, using the QUIJOTE line survey.
No lines of any isomer were found in this astronomical source, but
the experimental data will serve to enable future searches for these
species in the ISM.