title: Photoinduced radical processes on the spinel (MgAl2O4) surface involving methane, ammonia, and methane/ammonia.
abstract: The present study explored photoinduced radical processes caused by interaction of CH(4) and NH(3) with a photoexcited surface of a complex metal oxide: magnesium-aluminum spinel (MgAl(2)O(4); MAS). UV irradiation of MAS in vacuo yielded V-type color centers as evidenced by the 360 nm band in difference diffuse reflectance spectra. Interaction of these H-bearing molecules with photogenerated surface-active hole states (O(S)(-)•) yielded radical species which on recombination produced more complex molecules (including heteroatomic species) relative to the initial molecules. For the MAS/CH(4) system, photoinduced dissociative adsorption of CH(4) on surface-active hole centers produced •CH(3) radicals that recombined to yield CH(3)CH(3). For MAS/NH(3), a similar dissociative adsorption process led to formation of •NH(2) radicals with formation of NH(2)NH(2) as an intermediate product; continued UV irradiation ultimately yielded N(2). For the mixed MAS/CH(4)/NH(3) system, however, interaction of adsorbed NH(3) and CH(4) on the UV-activated surface of MAS yielded •NH(2) and •CH(3) radicals, respectively, which produced CH(3)-NH(2) followed by loss of the remaining hydrogens to form a surface-adsorbed cyanide, CN(S), species. Recombination of photochemically produced radicals released sufficient energy to re-excite the solid spinel, generating new surface-active sites and a flash luminescence (emission decay time at 520 nm, τ ~ 6 s for the MAS/NH(3) case) referred to as the PhICL effect.
authors.affiliation: Faculty of Physics, Saint-Petersburg State University, Saint-Petersburg, Russian Federation. alexei.emeline@spbu.ru
authors.forename: A V
authors.initials: AV
authors.lastname: Emeline
authors.forename: D A
authors.initials: DA
authors.lastname: Abramkin
authors.forename: I S
authors.initials: IS
authors.lastname: Zonov
authors.forename: N V
authors.initials: NV
authors.lastname: Sheremetyeva
authors.forename: A V
authors.initials: AV
authors.lastname: Rudakova
authors.forename: V K
authors.initials: VK
authors.lastname: Ryabchuk
authors.forename: N
authors.initials: N
authors.lastname: Serpone