Photochemical Decomposition of Aqueous Permanganate Ion

Abstract

Quantum yields for the photochemical decomposition of aqueous MnO4— have been measured under a variety of conditions using a sensitive method for measuring O2 production, first developed by Pringsheim and co-workers. The quantum yield was found to depend strongly on the wavelength of the light, slightly on temperature at the longer wavelengths, and not at all on the composition of the solution or on light intensity. Additional experiments were carried out which showed that the isotopic composition of photochemically produced O2 was independent of the O-isotopic composition of the solvent water. These results lead to the conclusion that the radiant energy absorbed by the MnO4— ion is converted with high probability into vibrational energy of the ground state, after which the ion dissociates thermally into MnO2 and O2 (in a single act) or cools down without dissociation (the position of the extra electron is uncertain). A possible quantitative theory which predicts fairly successfully the dependence of the quantum yield on wavelength is outlined.

Universal behavior of photochemical deposition in liquid solutions driven by a one-photon transition

“…Beyond the investigation of deposition by photodissociation, the well-known reduction of permanganates is considered as the simplest way to produce manganese dioxide, which is widely used as a catalyst 64 , as the active cathode material in a range of modern batteries 65,66 , and as a scavenger or a decolorizer. This wide range of applications illustrates why irradiation by UV light was also prompted to prepare hybrid materials by photodeposition ( polyimide MnO 2 as organic-inorganic nanocomposites 67 and Even if the photodissociation of permanganates has been known for a long time 70 , this is only recently that the involved mechanisms were clearly identified 71,72 . The following reaction scheme is now We consider here the seminal experimental investigation performed by Peled and his collaborators on the deposition of amorphous selenium films driven by discharge lamps and filament sources , and further extended with continuous-wave laser irradiation .…”

Photodecomposition of MnO4-: A Theoretical Study

“…Kläning and Symons 6 have discussed the accessibility of several light-induced decomposition channels for MnO 4 -such as and speculated that the most probable route for oxygen formation is channel 1, in agreement with the conjecture of Zimmerman. 5 We will show later that the photofragmentation of MnO 4 -from its ground state through either channel 1 or 2 requires energies in excess of 5 eV. Thus, these direct channels cannot be accessed with visible light.…”

Formation of Superoxochromium(III) by a Novel Mechanism

“…Thus, permanganate ion is known to suffer an internal redox transformation when activated by u.v. irradiation with decomposition into Mn III O À 2 and O 2 , the oxygen atoms of this gas coming from permanganate and not from the solvent [39], and a manganese(V) monoperoxo complex, ½Mn V ðOÞ 2 ðO 2 Þ À , with a structure similar to that of the chromium(IV) monoperoxo complex formed in Scheme 2, has been postulated as the intermediate involved in the process [40]. Thus, although chromate ion does not decompose by photolysis as permanganate ion does [41], complexation with thiols might play in the case of chromate the same activation role as u.v.…”