Structure of Furan from 44 IsotopologuesResolving Differences in the Theoretical (r_e) and Semi-Experimental Equilibrium (r_e^SE) Structures

High-temperature, high-pressure, base-catalyzed H/D exchange was employed to create a mixture of all possible furan-<i>d</i>_<i>x</i> isotopologues, allowing for the measurement and analysis of the rotational spectra of 44 furan isotopologues. The experimental rotational constants of these isotopologues, combined with CCSD(T)/cc-pCVTZ corrections for the effects of vibration–rotation interaction and the electron-mass distribution, were used to determine a semi-experimental equilibrium (<i>r</i>_<i>e</i>^SE) structure of furan.

The large number of isotopologues used, including 35 isotopologues observed for the first time, allowed for the determination of the <i>r</i>_<i>e</i>^SE structure to a high level of accuracy and precision (≤0.0003 Å uncertainties in bond distances and ≤0.02° in bond angles). The current study additionally corrects for differences in principal axis rotation between the structure at which the vibration–rotation interaction constants were evaluated (CCSD(T)/cc-pCVTZ) and the <i>r</i>_<i>e</i>^SE structure.