First principles study of ortho–para H2 conversion on the O2(0.25 ML)/Ag(111) system

We investigated the ortho–para (o–p) H2 conversion on the O2/Ag(111) system, combining first principles calculations based on spin-polarized density functional theory with perturbative calculations. In this study, we calculated the o–p H2 conversion rate, using the standard Fermi's Golden Rule and compared the contribution efficacy of the magnetic dipole interaction and the Fermi contact interaction. The calculated o–p H2 conversion times induced by the magnetic dipole interaction and by the Fermi contact interaction, corresponding to the reciprocal of the o–p H2 conversion rates, are in the orders of 100–103 s and 100–106 s, respectively. In comparison with the o–p H2 conversion time of 610 s on clean Ag surfaces, these results indicate that the magnetic dipole interaction and the Fermi contact interaction enhance the o–p H2 conversion in the vicinity of O2. In addition, the magnetic dipole interaction and the Fermi contact interaction can be separately observed with the different distances between H2 and O2.