Weak carbonyl-methyl intermolecular interactions in acetone clusters explored by IR plus VUV spectroscopy

Size-selected IR-VUV spectroscopy is employed to detect vibrational characteristics in the region 2850 similar to 3550 cm(-1) of neutral acetone and its clusters (CH3COCH3)(n) (n = 1-4). Features around 3440 cm(-1) in the spectra of acetone monomer and its clusters are assigned to the carbonyl stretch (CO) overtone. These features red-shift from 3455 to 3433 cm(-1) as the size of the clusters increases from the monomer to the tetramer. Based on calculations, the experimental IR spectra in the C=O overtone region suggest that the dominant structures for the acetone trimer and tetramer should be cyclic in the supersonic expansion sample. This study also suggests that the carbonyl groups interact with the methyl groups in the acetone clusters. These weak interactions are further confirmed by the use of deuterium substitution. (C) 2012 Elsevier B.V. All rights reserved.