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oai:figshare.com:article/34018491 2026-09-28T21:03:35Z category_1 category_4 category_7 category_19 category_24 category_873 category_39 category_45 category_734 category_64 portal_63 item_type_3 month_year_09_2026

Rotational Spectroscopy and Partial Semi-Experimental Equilibrium (r_e^SE) and Substitution (r_s^SE) Structures of Cyclobutenone (c‑C₄H₄O) Brian J. Esselman (1470556) Michael J. Carrillo (5842223) Madeleine G. Atwood (11077933) Nitai P. Sahoo (23789790) Zoe K. Deems (25133346) Michael J. Tubergen (1903726) Maria A. Zdanovskaia (11002543) R. Claude Woods (2043850) Robert J. McMahon (752679) Biophysics Biochemistry Medicine Pharmacology Evolutionary Biology Chemical Sciences not elsewhere classified Ecology Sociology Biological Sciences not elsewhere classified Cancer two different sets experimental equilibrium (< equilibrium values (< ground vibrational state highly strained four substitution (< italic state hamiltonian model >< sub >< singly substituted heavy sextic centrifugally distorted level electron correlation rotational constants (< se </ sup cyclobutenone (< italic ></ sub >, 21 </ sub 20 </ sub 4 </ sub sup >< substitution (< state hamiltonian >< sub sextic distorted ></ sup four lowest cyclobutenone (< ></ sub rotational spectrum rotational spectroscopy μ </ e </ Partial semi-experimental equilibrium (<i>r</i>_<i>e</i>^SE) and substitution (<i>r</i>_<i>s</i>^SE) structures of cyclobutenone (<i>c</i>-C₄H₄O, <i>C</i>_<i>s</i>, <i>μ</i>_<i>a</i> = 3.4 D) have been determined for the first time via rotational spectroscopy. The rotational spectrum of this reactive species, which contains a highly strained four-membered ring, has been measured from 9 to 735 GHz. Over 3800 transitions for the ground vibrational state of the normal isotopologue of cyclobutenone were measured, assigned, and least-squares fit to sextic distorted-rotor A- and S-reduced Hamiltonians in the I^<i>r</i> representation, providing a complete set of quartic and sextic centrifugal distortion parameters. Rotational transitions for each of the singly substituted heavy-atom isotopologues were measured at natural abundance. Rotational constants (<i>B</i>₀) for the six isotopologues were converted to equilibrium values (<i>B</i>_<i>e</i>) using CCSD(T)/cc-pCVTZ vibration-rotation interaction and electron-mass corrections, enabling the determination of partial <i>r</i>_<i>e</i>^SE and <i>r</i>_<i>s</i>^SE structures that define all of the heavy-atom parameters of cyclobutenone. The two different sets of semi-experimental structural parameters (<i>r</i>_<i>e</i>^SE and <i>r</i>_<i>s</i>^SE) are compared to the “best theoretical estimate” (BTE <i>r</i>_<i>e</i>) values, which are derived from the CCSD(T)/cc-pCV5Z <i>r</i>_<i>e</i> structure with additional corrections addressing finite basis set, higher-level electron correlation, and relativistic effects, as well as incorporating the diagonal Born–Oppenheimer correction. Additionally, transitions of the four lowest-energy vibrationally excited states have been assigned, measured, and least-squares fit to A-reduced, sextic centrifugally distorted-rotor Hamiltonians in the I^<i>r</i> representation. While ν₂₁ was well-modeled using a single-state Hamiltonian, 2ν₂₁, ν₁₄, and ν₂₀ form an anharmonic- and Coriolis-coupled triad and were treated by a three-state Hamiltonian model. 2026-09-28T00:00:00Z Dataset Dataset 10.1021/acs.jpca.6c04937.s002 https://figshare.com/articles/dataset/Rotational_Spectroscopy_and_Partial_Semi-Experimental_Equilibrium_r_sub_e_sub_sup_SE_sup_and_Substitution_r_sub_s_sub_sup_SE_sup_Structures_of_Cyclobutenone_c_C_sub_4_sub_H_sub_4_sub_O_/34018491 CC BY-NC 4.0