COMPARATIVE ANALYSIS OF THE CAPABILITIES OF MOLECULAR SPECTROSCOPY METHODS IN STUDYING INTERNAL ROTATION

Abstract

In the review the comparison of the methods used to study internal rotation (IR) in the ground (S0) and excited (S1) electronic states in the series of α,β-unsaturated carbonyl compounds: R4R3C = CR2-COR1, where R1 = H, R1 = F, R1 = CI; R2 = H, R2 = CH3, R2 = F; R3 = R4 = H = CH3, is made. 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 n-π*-transition of high-resolution UV absorption spectra and IR-Fourier-spectra, used in the study (IR) in (S0) electronic state. The reasons for such differences are established. It is shown that in the (S0) state a more reliable determination of the values of (0-v)-transitions of torsional vibration of both isomeric forms of molecules was obtained in the method of analysis of the vibrational structure of n-π*-transition of UV absorption spectra. A new assignment for transitions of torsional vibration of the s-trans isomer of acrolein in the spectrum of the Cavity Ringdown Spectroscopy (CRDS) method in the excited (S1) state is proposed. It is concluded that the method of analyzing the vibrational structure of n-π*-transition of high-resolution UV absorption spectra of vapors of the studied compounds is more reliable and accurate when studying (IR) in both electronic states.