Abstract
Photon-stimulated desorption of positive ions from thin film DNA components, 2-deoxy- d-ribose, thymine and guanine, were investigated in the oxygen K-edge excitation region. H +, CH 2 +, C 2H 2 +, CHO +, C 3H 3 + and C 2HO + were desorbed mainly from the 2-deoxy- d-ribose thin film following oxygen K-edge excitation. The ion yields were obtained as a function of the photon energy. Each spectrum showed a prominent peak structure coinciding with the O 1 s→ σ ∗ (C–O) excitation energy. These results indicate that the observed ions are produced not only by direct photodecomposition but also by the impact of secondary electrons that the core excitation generates. On the other hand, H + has been observed by irradiation of thymine and guanine thin films, while only insignificant amounts of the other ions were observed. It is shown that the core excitation more drastically degraded the 2-deoxy- d-ribose molecule into small fragments than is the case with the nucleobases. The sugar moiety in DNA is likely to be one of the nor fragile molecular sites, conducive to a single-strand DNA break.
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