Photolysis of Ammonia in a Solid Matrix at Low Temperatures

Abstract

Solid deposits of argon containing 0.3 mole % ammonia were irradiated at 4.2°K with light of wavelengths shorter than 2000 A. The emission of a hydrogen discharge with a LiF window and of a thin‐walled quartz mercury arc were used. The production of the unstable species NH and NH₂ was observed by means of electronic absorption spectroscopy. Experiments using filters led to the conclusion that NH is produced by irradiation with light of wavelengths shorter than 1550 A. NH₂ is produced by radiation above 1700 A and below 1550 A with comparable quantum efficiency. Warmup experiments show that NH₂ disappears close to 20°K whereas NH is stable up to at least 36°K. Photolysis at 20°K is approximately five times less efficient than at 4.2°K. On certain assumptions a molar absorption coefficient of 40 000 is estimated for both NH and NH₂ and the f values of the observed transitions of these molecules are estimated to be of the order of 10^—3.