Water-Related Matrix Isolation Phenomena during NO 2 Photolysis in Argon Matrix

Abstract

Photolysis (350–450 nm) of NO₂ molecules trapped in argon matrices at 10 K has been studied using Fourier transform infrared (FT-IR) spectroscopy to examine the mobility of the photolysis products, O(³P) and NO, and their subsequent reactions. The formation of N₂O₅ and N₂O₃ from reactions of these mobile species with immobilized NO₂ and N₂O₄ is confirmed. Water molecules from the background gases in the vacuum have been found to be isolated in the argon matrix during deposition of diluted NO₂ in Ar. The entrapped water molecules along with some of their NO₂ adducts have been characterized. Exposure of the matrix to photons to photolyze NO₂ resulted in not only internal matrix reactions, but also an enhanced deposition of ice over the surface of the argon matrix. This is caused by photodesorption of water molecules from the walls of the matrix isolation chamber and their subsequent condensation on the matrix surface. This ice overlayer has been found to give a very significant dangling OH band and a substantial librational band in the FT-IR spectra, indicating substantial surface area and internal porosity, respectively. The potential of using photodesorbed water to establish high surface area ice interfaces with dangling OH groups for heterogeneous photoreaction studies is discussed.