The 1,2- dichloroethane (DCE)/water interface is important because of its suitability as an electrochemical interface between two immiscible electrolyte soloutions. An issue of particular interest is whether the interfacial region is molecularly sharp or is comprised of a diffuse mixed interfacial region. Optical sum-frequency and recent neutron measurements suggest the interface is broader than can be accounted for by capilary waves alone although molecular dynamics simulations suggest it should be sharp on a molecular level.One novel way to approach this problem is to study the vapour/DCE interface using controlled water humidity. An increase in interfacial roughness with increasing humidity would be expected if interfacial mixing occurs.