ESR study of monomer and triplet state dimer NO adsorbed on sulfated zirconia

Triplet state NO dimers stabilized on the surface of sulfated zirconia (g(p erpendicular to)= 1.993, g(parallel to) = 1.942, D-perpendicular to = 195 G , E approximate to 0) have been observed by ESR. They are formed by adsorpt ion of NO molecules on pair (acceptor) surface sites represented, most like ly, by two adjacent (d=5.2 Angstrom) low-coordinated Zr4+ ions. A new singl e line (Lorentz line with g = 1.993 and line width 18 G) of NO monomers ads orbed on active sites of sulfated zirconia has been observed. The sites whe re this form is stabilized seem to be very strong electron accepters respon sible for the formation of radical cations after adsorption of aromatic mol ecules, (C) 2000 Elsevier Science B.V. All rights reserved.