Comparative Analysis of the Capabilities of Molecular Spectroscopy Methods in Studying Internal Rotation

• Published in: Moscow University chemistry bulletin 2023-12, Vol.78 (6), p.299-313
• Main Authors: Koroleva, L. A., Koroleva, A. V.
• Format: Article
• Language: English
• Subjects: Absorption spectra; Carbonyl compounds; Carbonyls; Cavity ringdown; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Electron states; Fourier transforms; High resolution; Infrared spectroscopy; Isomers; Molecular spectroscopy; Rotation; Spectrum analysis; Torsional vibration
• ISSN: 0027-1314; 1935-0260
• DOI: 10.3103/S0027131423060056

In this review, the methods used to study internal rotation in the ground (S 0 ) and excited (S 1 ) electronic states in the following series of α,β-unsaturated carbonyl compounds: R 4 R 3 C = CR 2 –COR 1 , where R 1  = H, R 1 = F, R 1 = C I ; R 2 = H, R 2 = CH 3 , R 2 = F; and R 3 = R 4 = H = CH 3 , are compared. Differences in the values of (0-v)-transitions of torsional vibration for s- trans - and s- cis -isomers for some studied compounds are revealed in the methods of analysis of the vibrational structure of the n -π*-transition of high-resolution UV absorption spectra and Fourier-transform IR spectra used in the study of the internal rotation in the (S 0 ) electronic state. The reasons for such differences are established. It is shown that in the (S 0 ) state, a more reliable determination of the values of (0-v)-transitions of the torsional vibration of both isomeric forms of molecules is obtained in the method of analysis of the vibrational structure of n -π*-transition of UV absorption spectra. A new assignment for transitions of the torsional vibration of the s- trans isomer of acrolein in the spectrum of the cavity ringdown spectroscopy (CRDS) method in the excited (S 1 ) state is proposed. It is concluded that the method of analyzing the vibrational structure of the n -π*-transition of high-resolution UV absorption spectra of vapors of the studied compounds is more reliable and accurate when studying the internal rotation in both electronic states.