The puzzling hyper-fine structure and an accurate equilibrium geometry of succinic anhydride

• Published in: Physical chemistry chemical physics : PCCP Vol. 22; no. 9; pp. 5170 - 5177
• Main Authors: Jahn, Michaela K, Obenchain, Daniel A, Nair, K P Rajappan, Grabow, Jens-Uwe, Vogt, Natalja, Demaison, Jean, Godfrey, Peter D, McNaughton, Don
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 04.03.2020
• Subjects: Anhydrides; Chemical equilibrium; Equilibrium; Fine structure; Fourier transforms; Millimeter waves; Rotational spectra; Rotational states; Spectrum analysis
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c9cp06775b

An accurate semiexperimental equilibrium structure of succinic anhydride has been determined from a combination of experiment and theory. The cm-wave and mm-wave rotational spectra of succinic anhydride, 3,4-dihydrofuran-2,5-dione, were recorded in a pulsed supersonic jet using Fourier-transform microwave spectroscopy and in a free-jet using mm-wave absorption spectroscopy. Many lines in the cm-wave spectrum show fine structure and after eliminating all other possibilities the origin of this fine structure is determined to be from spin-spin interaction. Accurate rotational and quartic centrifugal distortion constants are determined. Assignments of 13C and 18O singly substituted isotopologues in natural abundance were used to obtain a substitution geometry for the heavy atoms of succinic anhydride. Theoretical approaches permitted the calculation of a Born-Oppenheimer ab initio structure and the determination of a semiexperimental equilibrium structure in which computed rovibrational corrections were utilized to convert vibrational ground state rotational constants into equilibrium constants. The agreement between the semiexperimental structure and the Born-Oppenheimer ab initio structure is excellent. Succinic anhydride has been shown to have a planar heavy atom equilibrium structure with the effects of a large amplitude vibration apparent in the resultant rotational constants.