The photodecomposition of 1, 1, 1-trichloro-2, 2-bis (5'-chloro-2'-methoxyphenyl) ethane (MPA) has been carried out both in solution and solid phase with exciting light> 300 nm. The major products of the solid phase photolyses are HCl and 1, 1-dichloro-2, 2-bis (5'-chloro-2'- methoxyphenyl) ethylene (MPE), 5, 5'-chloro-2, 2'-methoxybenzophenone (MPO), 1, 1- dichloro-2, 2-bis (5'-chloro-2'-methoxyphenyl) ethane (MPD), and 1-chloro-2, 2-bis (5'- ...