ESR of adsorbates on single crystal metal surfaces under UHV conditions

Angular dependent electron spin resonance measurements were taken for paramagnetic molecules adsorbed on metallic single crystal surfaces in UHV. For the hydrated Cu(NO₃)₂ complex on a Cu111] surface an angular dependent ESR signal is recorded. The plane ofthe molecule is found to lie preferentially out of the surface plane. Experiments on chemisorbed molecular O₂ on Ag110] at 25 K and NO on Pt111] at 110 K show no sharp ESR signal characteristic for well localized moments. If one assumes that NO on Pt (respectively Pd) carries an unpaired spin, one can estimate a lower limit for the spin flip rate of π^?1>2×10⁹s^?.