Impact of temperature and polarization on NEXAFS spectra of adenine localized on a polycrystalline copper surface

The features of the near edge X-ray absorption fine structure (NEXAFS) were studied as a function of the applied external temperature and polarization in a system of localized adenine molecules on polycrystalline copper surfaces deposited by wet-chemical methods. The resulting adenine//copper surfaces were annealed at temperatures ranging from 298 K to 473 K for analysis of the NEXAFS N K-edge spectrum characteristics. The dependence of the N K-edge on the polarization angle was studied at two different angles by rotating the substrate holder in the analytical chamber relative to the incoming synchrotron beam. We found that polarization has a greater effect on the electron density distribution in NEXAFS N K-edge spectra of adenine than the external temperature gradient applied to the surface. Our results show that the dependence of the absorption intensity of π * resonance on the polarization angle is due to a significant difference in the distribution of the π * electron density, which reveals the specific orientation of the adenine molecule on the Cu-based surface. These results provide insight into the atomic and electronic structure of adenine//Cu and contribute to a possible explanation of the vibrational spectra of adenine, which are strongly dependent on the orientation of the molecule on the surface.