| Abstrakt: |
The gas phase photodissociation spectra of four protonated β-diketones were obtained and compared with the absorption spectra of the corresponding ions in solution. Protonated 2,4-pentanedione was observed to undergo the photodissociation process [C5H9O2]+ +hν → [CH3CO]+ +C3H6O with a λmax at 276±10 nm compared with a solution absorption maximum at 286 nm. Protonated 2,4-hexanedione was observed to undergo the photodissociation processes [C6H11O2]+ +hν → [CH3CO]+ +C4H8O and [C6H11O2]+ +hν → [C2H5CO]+ +C3H6O with a λmax at 279±10 nm compared with a solution absorption maximum at 288 nm. Protonated 3-methyl-2,4-pentanedione was observed to undergo the photodissociation process [C6H11O2]+ +hν → [CH3CO]+ +C4H8O with a λmax at 295±10 nm compared with a solution absorption maximum at 305 nm. Protonated 1,1,1-trifluoro-2,4-pentanedione was observed to undergo the photodissociation process [C5H6F3O2]+ +hν → CF3H+[C4H5O2]+ with a λmax at 273±10 nm compared with a solution absorption maximum at 288 nm. The [CH3CO]+ and [C2H5CO]+ produced photochemically with the first three ions react to regenerate the protonated β-diketone leading to a photostationary state. Photodissociation of the protonated alkyl β-diketones is believed to occur from the protonated keto form, whereas photodissociation of protonated 1,1,1-trifluoro-2,4-pentanedione is believed to occur from the protonated enol form. Mechanisms for the observed photodissociation processes are proposed and comparisons with results from related techniques are presented. [ABSTRACT FROM AUTHOR] |
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