Isomerization of Nitrous Acid: An Infrared Photochemical Reaction

Abstract

Nitrous and deuteronitrous acid suspended in nitrogen matrices at 20°K isomerize when illuminated with infrared light. Kinetic studies indicate that both the cis to trans and the trans to cis isomerizations occur. Filter studies show that a narrow range of frequencies is responsible, 3650–3200 cm—1 for HONO and 4100–3500 cm—1 for DONO. An isomerization mechanism is proposed that involves a highly efficient intramolecular transfer of energy between vibrational modes. The height of the potential barrier to isomerization is estimated to be 9.7±0.7 kcal/mole in the matrix and 8.7±1 kcal/mole for gaseous HONO. Comparison to methyl nitrite suggests that the bondings in these two molecules are quite similar and that the reported structure of methyl nitrite is incorrect.