Isotopic dilution, self-association, and Raman non-coincidence in the binary system (CH3)2CO+(CD3)2CO reinvestigated by polarized Raman measurement and ab initio calculations

Abstract

Abstract Raman spectra of the binary system (CH 3 ) 2 CO (acetone)+(CD 3 ) 2 CO (acetone-d 6 ) were reinvestigated employing a more precise and sensitive scanning multichannel detection scheme. The I ∥ and I ⊥ components of the Raman scattered radiation were recorded in the CO stretching region, 1600–1800 cm −1 as well as in the C–D and C–H stretching regions, 2000–2300 and 2800–3100 cm −1 , respectively, in different mixtures with the varying mole fractions of the reference system. A careful Raman line shape analysis yielded after fit Δ ν nc due to Raman non-coincidence effect (NCE) in acetone and acetone-d 6 as 4.87±0.01 and 4.49±0.01 cm −1 , respectively. The optimized geometries and wavenumbers of the neat acetone molecule and its self-associated structure were calculated using ab initio method at the MP2 level using 6-31++G(d,p) basis set. The influence of self-association and NCE together were examined. A systematic study of Raman line shape analysis led to a hitherto unexplored aspect, the wavenumber shift and linewidth variation of the ν 1 (C–H) stretching mode of acetone upon isotopic dilution. The linewidth variation with the mole fraction of the reference system shows an excellent agreement with the corresponding linewidths derived from the T 2 values obtained by three color fs-CARS study reported earlier.