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

Raman spectra of the binary system (CH3)2C=O (acetone)+(CD3)2C=O (acetone-d6) 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 Δνnc due to Raman non-coincidence effect (NCE) in acetone and acetone-d6 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 ν1(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. © 2003 Elsevier B.V. All rights reserved.