Modification of the Optical Spectrum of Cytosine by the Formation of an Ordered Monolayer of Molecules at a Au(110)/Electrolyte Interface

Abstract

An analysis of the reflection anisotropy spectrum (RAS) of an ordered monolayer of cytosine adsorbed at a Au(110)/electrolyte interface is found to contain optical contributions from both the substrate and the cytosine. The spectrum of cytosine in an aqueous environment is significantly broadened by the interaction between the molecule and the Au(110). Successful simulations of the Au(110)/cytosine interface consisting of two additional molecular transitions, which sit in the middle of previously observed molecular absorption bands, are produced by an empirical Lorentzian transition model that is consistent with previous theoretical and experimental studies. While this analysis alone cannot determine the number of π→π* dipole transitions, it confirms that the only cytosine transitions that contribute to the optical response of the Au(110)/cytosine interface are located in the plane of the molecule, which is vertical to the gold surface with the long axis along the [1$\bar 1$0] direction.