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The rotational spectrum of 3-furonitrile has been collected from 85 to 500 GHz, spanning the most intense rotational transitions observable at room temperature. The large dipole moment imparted by the nitrile substituent confers substantial intensity to the rotational spectrum, enabling the observation of over 5600 new rotational transitions. Combined with previously published transitions, the available data set was least-squares fit to partial-octic, distorted-rotor A- and S-reduced Hamiltonian models with low statistical uncertainty (σfit < 0.031 MHz) for the ground vibrational state. Similar to its isomer 2-furonitrile, the two lowest-energy vibrationally excited states of 3-furonitrile (ν17, ν24), which correspond to the in-plane and out-of-plane nitrile bending vibrations, form an a- and b-axis Coriolis-coupled dyad. Rotationally resolved infrared transitions (30−600 cm−1) and over 4200 pure rotational transitions for both ν17 and ν24 were fit to a partial-octic, Coriolis-coupled, two-state Hamiltonian with low statistical uncertainty (σfit rot < 0.045 MHz, σfit IR < 6.1 MHz). The least-squares fitting of these vibrationally excited states provides their accurate and precise vibrational frequencies (ν17 = 168.193 164 8 (67) cm−1 and ν24 = 169.635 831 5 (77) cm−1) and seven Coriolis-coupling terms (Ga, GaJ, GaK, Fbc, FbcK, Gb, and Fac). The two fundamental states exhibit a notably small energy gap (1.442 667 (10) cm−1) and an inversion of the relative energies of ν17 and ν24 compared to those of the isomer 2-furonitrile. The rotational frequencies and spectroscopic constants of 3-furonitrile that we present herein provide a sufficient basis for conducting radioastronomical searches for this molecule across the majority of the frequency range available to current radiotelescopes.
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Complete, Theoretical Rovibronic Spectral Characterization of the Carbon Monoxide, Water, and Formaldehyde Cations
New high-level ab initio quartic force field (QFF) methods are explored which provide spectroscopic data for the electronically excited states of the carbon monoxide, water, and formaldehyde cations, sentinel species for expanded, recent cometary spectral analysis. QFFs based on equation-of-motion ionization potential (EOM-IP) with a complete basis set extrapolation and core correlation corrections provide assignment for the fundamental vibrational frequencies of the A˜2B1 and B˜2A1 states of the formaldehyde cation; only three of these frequencies have experimental assignment available. Rotational constants corresponding to these vibrational excitations are also provided for the first time for all electronically excited states of both of these molecules. EOM-IP-CCSDT/CcC computations support tentative re-assignment of the ν1 and ν3 frequencies of the B˜2B2 state of the water cation to approximately 2409.3 cm−1 and 1785.7 cm−1, respectively, due to significant disagreement between experimental assignment and all levels of theory computed herein, as well as work by previous authors. The EOM-IP-CCSDT/CcC QFF achieves agreement to within 12 cm−1 for the fundamental vibrational frequencies of the electronic ground state of the water cation compared to experimental values and to the high-level theoretical benchmarks for variationally-accessible states. Less costly EOM-IP based approaches are also explored using approximate triples coupled cluster methods, as well as electronically excited state QFFs based on EOM-CC3 and the previous (T)+EOM approach. The novel data, including vibrationally corrected rotational constants for all states studied herein, provided by these computations should be useful in clarifying comet evolution or other remote sensing applications in addition to fundamental spectroscopy.
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- Award ID(s):
- 1757220
- PAR ID:
- 10417593
- Date Published:
- Journal Name:
- Molecules
- Volume:
- 28
- Issue:
- 4
- ISSN:
- 1420-3049
- Page Range / eLocation ID:
- 1782
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/molecules28041782
