Chemical Reactions in Molecular Sieves. I. NO3 Free Radical from Direct Reaction of NO2 and Atomic Oxygen

NO2 adsorbed in the cavities of 13-X molecular sieve reacts with oxygen atoms from a microwave discharge to form the NO3 free radical which remains trapped within the cavities. The EPR spectrum of the NO3 at 300°K is a single symmetrical line with g=2.019 and 11 G width between points of maximum slope. At 85°K a 5.9-G isotropic hyperfine coupling constant with the single 14N nucleus is resolved. The trapped NO3 free radical is apparently freely rotating even at 85°K. The odd-electron NO2 molecule is observed to exhibit free rotation in the 13-X sieve only down to ∼150°K.