Structure of Nitric Oxide Adsorbed on 4A Molecular Sieve

摘要

We have studied the ESR of nitric oxide (NO) adsorbed onto Linde 4A molecular sieve, and have observed that at least two different surfaces sites can be produced, depending on the nature of the surface activation process. Upon quench cooling the sieve activated at high temperature to 77deg;K, we find trapping of NO at metastable sites and subsequent migration to equilibrium sites. We have obtained the hyperfine interaction constants for NO absorbed onto the equilibrium sites. Comparison of these values with those of a series of molecules which can be formally considered as substituted nitric oxide radicals apparently rules out a model in which NO is singly coordinated to the surface. The comparison also suggests as a possible model NO doubly coordinated at nitrogen, and bridging two surface atoms.