Chirped-pulse Fourier-transform millimeter-wave rotational spectroscopy of furan in its v10 and v13 excited vibrational states

Furan, a prototypical heteroaromatic cyclic ether, is an important molecule that has garnered attention from a wide range of fields, from food and health research to combustion and atmospheric chemistry. Chirped-pulse Fourier-transform rotational spectroscopy of jet-cooled furan in the W-band across three narrow regions 79.3-79.45 GHz, 88.6-88.8 GHz, and 97.95-98.15 GHz is reported here. A pyrolysis nozzle was used to efficiently populate vibrationally excited states of low-frequency modes. Apart from the v = 0 state, vibrationally excited v = 1 states of modes v₁₁, v₁₄, v₁₀, and v₁₃ were observed. Furan is a planar molecule and these observed excited state modes correspond to out-of-plane vibrations. The v = 0 state and the vibrationally excited v₁₁ and v₁₄ were previously recorded and fit by Barnum et al (T. J. Barnum, K. L. K. Lee, B. A. McGuire, ACS Earth Space Chem. 5 (2021), 2986-2994). Rotational transitions in the J"=5 to 9 rotational states were fit for the previously undetected v₁₀ mode and experimental linelists for v = 1 states of modes v₁₀ and v₁₃ are provided, both of which are out-of-plane CH bending modes. Inertial defect was shown to be a useful quantity to extract structural information of vibrational modes of planar asymmetric tops. These rotational fits will assist astronomical searches for furan and its vibrational states.