Structure of photochemical reactor comprising: - a hollow container body having a side wall in a chemically inert material and arranged to contain an excited luminous plasma con electromagnetic fields and defining a closed excitation chamber in which an excitable material is present in such a way to obtain a discharge of said excited luminous plasma by microwave irradiation, said hollow container body being provided with: - at least a hollow which protrudes into said excitation chamber; - at least a source of microwave radiation positioned in said hollow, said source of microwave radiation arranged to emit said radiation, in such a way to excite said excitable material producing said luminous plasma arranged to emit an optical radiation having a predetermined wavelength; said photochemical reactor characterised in that said hollow is delimited by a wall which protrudes into said excitation chamber, whereby said source of microwave radiation is not into contact with said plasma and in that a reaction tube is, furthermore, provided arranged to pass through said excitation chamber, in such a way to be immersed in said luminous plasma, said reaction tube arranged to contain predetermined chemical reagents and being made of a material transparent to said predetermined optical radiation emitted by said luminous plasma, in such a way that said optical radiation is arranged to hit said chemical reagents in such a way to induce a predetermined photochemical reaction. - a hollow container body having a side wall in a chemically inert material and arranged to contain an excited luminous plasma con electromagnetic fields and defining a closed excitation chamber in which an excitable material is present in such a way to obtain a discharge of said excited luminous plasma by microwave irradiation, said hollow container body being provided with: - at least a hollow which protrudes into said excitation chamber; - at least a source of microwave radiation positioned in said hollow, said source of microwave radiation arranged to emit said radiation, in such a way to excite said excitable material producing said luminous plasma arranged to emit an optical radiation having a predetermined wavelength; said photochemical reactor characterised in that said hollow is delimited by a wall which protrudes into said excitation chamber, whereby said source of microwave radiation is not into contact with said plasma and in that a reaction tube is, furthermore, provided arranged to pass through said excitation chamber, in such a way to be immersed in said luminous plasma, said reaction tube arranged to contain predetermined chemical reagents and being made of a material transparent to said predetermined optical radiation emitted by said luminous plasma, in such a way that said optical radiation is arranged to hit said chemical reagents in such a way to induce a predetermined photochemical reaction. - at least a hollow which protrudes into said excitation chamber; - at least a source of microwave radiation positioned in said hollow, said source of microwave radiation arranged to emit said radiation, in such a way to excite said excitable material producing said luminous plasma arranged to emit an optical radiation having a predetermined wavelength;