Ortho-para conversion of hydrogen molecules on Cr2O3(0001)/Cr(110) surfaces

The Cr2O3(0001) surface can be terminated by Cr ions, which are either antiferromagnetically or ferromagnetically ordered. Ortho-para (o-p) conversion of H2 and para-ortho (p-o) conversion of D2 were investigated on such Cr2O3(0001)/Cr(110) surfaces by resonance-enhanced multiphoton ionization combined with photostimulated desorption. The natural conversion time of H2 and D2 was estimated to be 210 ± 22 s and 538 ± 57 s, respectively. The mechanism of the hydrogen nuclear-spin flip is discussed in terms of the magnetic structure of the Cr2O3(0001) surface.