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Luminescence and Raman spectra of acetylacetone at low temperatures (CROSBI ID 126531)

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Mohaček Grošev, Vlasta ; Furić, Krešimir ; Ivanković, Hrvoje Luminescence and Raman spectra of acetylacetone at low temperatures // The journal of physical chemistry. A, 111 (2007), 26; 5820-5827. doi: 10.1021/jp067157j

Podaci o odgovornosti

Mohaček Grošev, Vlasta ; Furić, Krešimir ; Ivanković, Hrvoje

engleski

Luminescence and Raman spectra of acetylacetone at low temperatures

Raman spectra of acetylacetone were recorded for molecules isolated in an argon matrix at 10 K and for polycrystalline sample. In solid sample broad bands appear superimposed on much weaker Raman spectrum corresponding to the stable Cs enol. Their position depends on the excitation wavelength (514.5 nm and 488.8 argon ion laser lines were used), sample temperature and cooling history. These bands are attributed to transitions from excited higher electronic state to various isomer states in the ground electronic state. Laser photons excite acetylacetone in crystal in the region where a number of excited triplet states are predicted for a free acetylacetone molecule (X.B. Chen et al. J. Phys. Chem. A 110 (2006) 4434.). Since singlet to triplet photon absorption transitions are forbidden, states existing in solid have mixed singlet/triplet character. Their decay results in population of different isomer states which are not vibrationally resolved except for the lowest isomers: Cs enol, C2v enol (here denoting possibly both TS1 and TS2 transition states described in Matanović and Došlić, J. Phys. Chem. A 109 (2005) 4185.), and keto form which can be detected in solid Raman spectra. Differential scanning calorimetry showed two signals on cooling of acetylacetone, one at 229 K and one at 217 K, while on heating they appear at 254 K and 225 K. The phase change at higher temperature is attributed to freezing/melting transition, while the one at lower temperature seems to correspond to freezing/melting of keto domains as suggested by Johnson et al. [ J. Chem. Phys. 116 (2002) 5694]. Using matrix isolation in argon technique, vibrational spectrum of acetylacetone at 10 K was recorded. Two bands at 3113 cm-1 and 3083 cm-1 are assigned to methyne CH stretching vibration of Cs and C2v enol conformers. Strong bands at 1602 cm-1 and 1629 cm-1 are assigned as Cs enol bands, and weaker underlying band at 1687 cm-1 and medium band at 1617 cm-1 as C2v enol bands.

fluorescence ; singlet-triplet mixing ; methyl group ; enol-keto tautomerism ; isomers

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Podaci o izdanju

111 (26)

2007.

5820-5827

objavljeno

1089-5639

1520-5215

10.1021/jp067157j

Povezanost rada

Fizika, Kemijsko inženjerstvo

Poveznice
Indeksiranost