Near-edge X-ray absorption fine structure of DNA nucleobases thin film in the nitrogen and oxygen K-edge region

Fujii, Kentaro; Akamatsu, Ken; Yokoya, Akinari

Near-edge X-ray absorption fine structure (NEXAFS) of evaporated DNA nucleobase thin films on to an Au-coated Si surface at room temperature has been investigated around the nitrogen and oxygen K-edge region using highly monochromatized synchrotron soft X-rays. Each nucleobase shows a specific absorption spectrum originating from resonant excitation of a 1s electron of nitrogen or oxygen to antibonding states, some of which strongly depend on the polarization angle of incident soft X-rays. From the analysis of polarization angle dependences for * resonant absorption intensity, purines are orientated to the multilayer surface with the angle 156 for adenine and 381 for guanine, respectively. Uracil has an orientation of 164, although other pyrimidines such as thymine and cytosine are randomly orientated to the surface.