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 (σ_fit = 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 (ν_24, 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 (σ_fit = 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, G, G, G, G, G, F, F, F, G, G, and F. 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.