A study of the primary processes in the photolysis of gaseous I-nitropropane at 22°C and 100 ± 1°C is undertaken. 1-Nitropropane undergoes a photochemical reaction giving rise to a six-member complex which produces ethylene, the major photolysis product. This is a typical intramolecular non-radical Norrish Type I1 process and is the most important primary process (1):