Is there sp3-bound H on epitaxial graphene? Evidence for adsorption on both sides of the sheet

► H adsorbed to graphene prepared on Ir (1 1 1) is studied using SFG spectroscopy. ► A line at a position characteristic for sp3-C-H-bonds is observed. ► This line is only prominent when H is mixed with D in the adsorbate. ► It is argued that symmetry arguments prohibit SFG-activity in a neat H layer. ► It is suggested that a local graphane structure is formed.