  The evidence for benzonitrile (C$_6$H$_5$CN}) in the starless cloud core
TMC-1 makes high-resolution studies of other aromatic nitriles and their
ring-chain derivatives especially timely. One such species is
phenylpropiolonitrile (3-phenyl-2-propynenitrile, C$_6$H$_5$C$_3$N), whose
spectroscopic characterization is reported here for the first time. The low
resolution (0.5 cm$^{-1}$) vibrational spectrum of C$_6$H$_5$C$_3$N} has been
recorded at far- and mid-infrared wavelengths (50 - 3500 cm$^{-1}$) using a
Fourier Transform interferometer, allowing for the assignment of band centers
of 14 fundamental vibrational bands. The pure rotational spectrum of the
species has been investigated using a chirped-pulse Fourier transform microwave
(FTMW) spectrometer (6 - 18 GHz), a cavity enhanced FTMW instrument (6 - 20
GHz), and a millimeter-wave one (75 - 100 GHz, 140 - 214 GHz). Through the
assignment of more than 6200 lines, accurate ground state spectroscopic
constants (rotational, centrifugal distortion up to octics, and nuclear
quadrupole hyperfine constants) have been derived from our measurements, with a
plausible prediction of the weaker bands through calculations. Interstellar
searches for this highly polar species can now be undertaken with confidence
since the astronomically most interesting radio lines have either been measured
or can be calculated to very high accuracy below 300 GHz.
