The influence of soft mode adsorbate vibrations on NEXAFS analyses: NO on Pd{110}

Abstract Near-edge X-ray absorption fine structure (NEXAFS) measurements have been performed on NO adsorbed on Pd“110” using a polarized light source at a range of incidence angles. An analysis of intensities of σ and π resonance features is made which includes both the average orientation of the molecule and contributions arising from a low frequency, in-plane hindered-translation mode. The analysis indicates that at all coverages NO is upright, with a hindered-translation mode frequency of 68 cm −1 directed along the azimuth. The normal frozen-molecule analysis would, incorrectly, yield a tilt angle of 22°; adsorbate molecular orientation cannot be reliably obtained from NEXAFS data at 300 K without including the effect of these high-amplitude modes.