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Final Report Summary - RAD-NANO-BIOMOL (Irradiation of model biomolecular nano-systems)

The exposure of living tissue to ionizing radiation can initiate mutations or cancers, effects that can be traced to the modification of DNA. Although sophisticated models of radiation effects are available, considerable refinements are necessary to understand the underlying mechanisms on the molecular scale. As part of a major multi-disciplinary response to this challenge, this project was centered on probing the effects of intermolecular bonding on the excited states, ionization energies, and fragmentation patterns of DNA bases and related biomolecules.

We have developed a new apparatus (Fig.1) at the Open University for multi-photon ionization (MPI) experiments on DNA / RNA bases and their hydrated clusters. Ions and cluster ions produced by successive photon absorption in ns laser pulses were identified by time-of-flight mass spectrometry. In the UV wavelengths used (220-230 nm), the simplest conceivable ionization scheme for these molecules is 2-photon absorption via a singlet * electronic excited state. However fast relaxation and dissociation can lead to more complex pathways requiring higher photon orders. The data acquisition system enabled ion flight times and photon fluence to be recorded on a pulse-by-pulse basis. Allied to small fluctuations in laser pulse intensity, this provided a novel and efficient means to determine the photon order for the production of specific ions.

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THE OPEN UNIVERSITY.
United Kingdom
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