Comment on "Liquid-Gas Interface of Iron Aqueous Solutions and Fenton Reagents".

A recent Letter in this Journal (Gladich et al. J. Phys. Chem. Lett. 13, 2994-3001) reported that photoelectron spectroscopy could not detect any products on the surface of aqueous Fe 2+ jets dosed with gaseous hydrogen peroxide. The Letter however concluded that Fe(aq) 2+ ions react with H 2 O 2 (g) at the water-vapor interface to produce the same Fe 3+ + HO • products as their reaction with H 2 O 2 (aq) in bulk water. We argue that this conclusion is untenable because nothing can be asserted about undetected species.