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|Type:||Artigo de periódico|
|Title:||The Kinetic Method As A Structural Diagnostic Tool: Ionized α-diketones As Loosely One-electron Bonded Diacylium Ion Dimers|
|Abstract:||The kinetic method is used to corroborate the description of ground state ionized α-diketones as loosely electron-bonded acylium ion dimers: R 1-C=O+ - e- - +O=C-R2. The abundance ratio of both the acylium ion fragments R1CO + and R2CO+ (summed to those of their respective secondary fragments) formed upon low energy (5 eV) collision-induced dissociation of several ionized α-diketones is found to correlate linearly with the ionization energies (IEs) of the corresponding R 1CO• and R2CO• free radicals as predicted by density functional theory calculations at the B3LYP/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 α-diketones are found to display an effective temperature of 1705 K, which indicates an intermediate loosely-bonded nature. B3LYP/6-311++G(d,p) optimized geometries and charge and spin densities also corroborate the description of ground state ionized α-diketones as loosely electron-bonded diacylium ion dimers.|
|Citation:||European Journal Of Mass Spectrometry. , v. 9, n. 4, p. 295 - 304, 2003.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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