The photoionization of thymine has been studied by using vacuum ultraviolet radiationa nd imaging photoelectronp hotoion coincidences pectroscopy after aerosol flash vaporization andb ulk evaporation.T he two evaporation techniquesh ave been evaluated by comparison of the photoelectrons pectra and breakdown diagrams. The adiabatic ionization energies for the first four electronic states were determined to be 8.922 AE 0.008,9 .851 AE 0.008, 10.30 AE 0.02, and 10.82 AE 0.01 eV.V ibrational features have been assigned for the first three electronic states with the help of Franck-Condon factor calculations based on densityf unctional theory and wave function theory vibrational analysis within the harmonic approximation. The breakdown diagram of thymine, as supported by composite methoda bi nitio cal-culations,s uggestst hat the main fragment ions are formed in sequential HNCO-, CO-, and H-loss dissociation steps from the thymine parenti on, with the first step corresponding to ar etro-Diels-Alder reaction. The dissociation rate constants were extractedf rom the photoion time-of-flight distributions and used together with the breakdown curvest oc onstruct as tatistical model to determine 0K appearance energies of 11.15 AE 0.16 and 11.95 AE 0.09 eV for the m/z 83 and 55 fragment ions, respectively.T hese results have allowedu st o revise previously proposed fragmentation mechanismsa nd to proposeamodel for the final, nonstatistical H-losss tep in the breakdown diagram, yielding the m/z 54 fragment ion at an appearance energy of 13.24 eV.

In a wide spectrum of neurodegenerative diseases, self-assembly of pathogenic proteins to cytotoxic intermediates is accelerated by the presence of metal ions such as Cu2+. Only low concentrations of these...