Laboratory blueprints for interstellar searches of aromatic chiral
  molecules: rotational signatures of styrene oxide
  The tracking of symmetry-breaking events in space is a longlasting goal of
astrochemists, aiming at an understanding of homochiral Earth chemistry. One
current effort at this frontier aims at the detection of small chiral molecules
in the interstellar medium. For that, high-resolution laboratory spectroscopy
data is required, providing blueprints for the search and assignment of these
molecules using radioastronomy. Here, we used chirped-pulse Fourier transform
microwave and millimeter-wave spectroscopy and frequency modulation absorption
spectroscopy to record and assign the rotational spectrum of the chiral
aromatic molecule styrene oxide, $\mathrm{C_{6}H_{5}C_{2}H_{3}O}$, a relevant
candidate for future radioastronomy searches. Using experimental data from the
2-12, 75-110, 170-220, and 260-330 GHz regions, we performed a global spectral
analysis, complemented by quantum chemistry calculations. A global fit of the
ground state rotational spectrum was obtained, including rotational transitions
from all four frequency regions. Primary rotational constants as well as
quartic and sextic centrifugal distortion constants were determined. We also
investigated vibrationally excited states of styrene oxide, and for the three
lowest vibrational states, we determined rotational constants including
centrifugal distortion corrections up to the sextic order. In addition,
spectroscopic parameters for the singly-substituted $^{13}$C and $^{18}$O
isotopologues were retrieved from the spectrum in natural abundance and used to
determine the effective ground state structure of styrene oxide in the gas
phase. The spectroscopic parameters and line lists of rotational transitions
obtained here will assist future astrochemical studies of this class of chiral
organic molecules.
