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|Type:||Artigo de periódico|
|Title:||The kinetic method as a structural diagnostic tool: ionized alpha-diketones as loosely one-electron bonded diacylium ion dimers|
|Abstract:||The kinetic method is used to corroborate the description of ground state ionized alpha-diketones as loosely electron-bonded acylium ion dimers: R'-C=O+---e(-)---O+=C-R-2. The abundance ratio of both the acylium ion fragments (RCO)-C-1* and (RCO+)-C-2 (summed to those of their respective secondary fragments) formed upon low energy (5 eV) collision-induced dissociation of several ionized alpha-diketones is found to correlate linearly with the ionization energies (IEs) of the corresponding (RCO.)-C-1 and (RCO.)-C-2 free radicals as predicted by density functional theory calculations at the B3LY/P/6-311++G(d,p) level. However, when these abundances are taken from 70 eV electron ionization mass spectra, lower and sometimes inverted ratios (2,3-pentanedione and 2,3-hexanedione) are observed. Inverted ratios are also observed via charge-exchange mass spectrometry/mass spectrometry (MS/MS) experiments for ionized 2,3-pentanodione formed with relatively high internal energies. Ionized alpha-diketones are found to display an effective temperature of 1705 K, which indicates an intermediate loosely-bonded nature. B3LY/P/6-311++G(d,p) optimized geometries and charge and spin densities also corroborate the description of ground state ionized alpha-diketones as loosely electron-bonded diacylium ion dimers.|
|Citation:||European Journal Of Mass Spectrometry. Im Publications, v. 9, n. 4, n. 295, n. 304, 2003.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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