Millimeter-Wave and High-Resolution Infrared Spectroscopy of 2‑FuronitrileA Highly Polar Substituted Furan

The rotational spectrum of 2-furonitrile
(2-cyanofuran)
has been
obtained from 140 to 750 GHz, capturing its most intense rotational
transitions at ambient temperature. 2-Furonitrile is one of two isomeric
cyano-substituted furan derivatives, both of which possess a substantial
dipole moment due to the cyano group. The large dipole of 2-furonitrile
allowed over 10 000 rotational transitions of its ground vibrational
state to be observed and least-squares fit to partial octic, A- and
S-reduced Hamiltonians with low statistical uncertainty (σfit = 40 kHz). The high-resolution infrared spectrum, obtained
at the Canadian Light Source, allowed for accurate and precise determination
of the band origins of its three lowest-energy fundamental modes (ν24, ν17, and ν23). Similar
to other cyanoarenes, the first two fundamental modes (ν24, A″, and ν17, A′, for 2-furonitrile)
form an a- and b-axis Coriolis-coupled
dyad. More than 7000 transitions from each of these fundamental states
were fit to an octic A-reduced Hamiltonian (σfit =
48 kHz), and the combined spectroscopic analysis determines fundamental
energies of 160.1645522 (26) cm–1 and 171.9436561
(25) cm–1 for ν24 and ν17, respectively. The least-squares fitting of this Coriolis-coupled
dyad required 11 coupling terms, Ga, GaJ, GaK, GaJJ, GaKK, Fbc, FbcJ, FbcK, Gb, GbJ, and FacK. Using both the rotational
and high-resolution infrared spectra, a preliminary least-squares
fit was obtained for ν23, providing its band origin
of 456.7912716 (57) cm–1. The transition frequencies
and spectroscopic constants provided in this work, when combined with
theoretical or experimental nuclear quadrupole coupling constants,
will provide the foundation for future radioastronomical searches
for 2-furonitrile across the frequency range of currently available
radiotelescopes.