Light-Induced cis-trans Isomerization of Nitrous Acid Formed by Photolysis of Hydrazoic Acid and Oxygen in Solid Nitrogen

Abstract

Photolysis of hydrazoic acid in solid nitrogen at 20°K with oxygen present yields both cis‐ and trans‐ nitrous acid. The identification is based on infrared detection of features of the isotopically substituted species HONO, DONO, and HO¹⁸NO¹⁸. The nitrous acid probably results from the reaction of imidogen with oxygen $$\mathrm{NH}+{\mathrm{O}}_2=\mathrm{HONO}.$$ Isomerization of nitrous acid occurs in the matrix at 20°K under the influence of irradiation. Ultraviolet radiation causes the trans‐ to cis‐ reaction, probably by electronic excitation to give a random mixture of the two forms. Near‐infrared radiation reverses the reaction but the role of the radiation is not known. Bulk heating of the sample is not involved and a broad range of near‐infrared frequencies is effective. No isomerization of DONO could be detected and HO¹⁸NO¹⁸ seemed to isomerize more slowly than did HONO. Only speculative interpretations of this phenomenon can be made at this time.