Vacuum Ultraviolet Photochemistry. III. Primary Processes in the Vacuum Ultraviolet Photolysis of Water and Ammonia

Abstract

Water and ammonia have each been photolyzed in the absence and presence of C2D4 which served to scavenge H atoms. Wavelengths used were: for ammonia, 1849 and 1236 A; for water, 1236 A. Under conditions where H atoms are efficiently scavenged by C2D4, the production of H2 signifies a primary photochemical process giving molecular H2 directly. It is found that at 1849 A, ammonia decomposes almost entirely to H+NH2. At 1236 A, two primary processes are observed. (a)NH3→H2+NH,(b)NH3→H+NH2.Process (a) is about ⅙ as probable as process (b). At 1236 A, the photolysis of water proceeds via two primary processes. (c)H2O→H+OH,(d)H2O→H2+O.The probability of process (c) being three times that of process (d). It is suggested that primary process (d) constitutes a reasonable photochemical mechanism for hydrogen formation in the earth's upper atmosphere.