Abstract
We have analysed the core-to-bound excitations in condensed NH 3 and CH 4 in the N1s and C1s regions, respectively, utilizing highly resolved synchrotron radiation. Photoabsorption (from partial electron yields) and photodesorption of H + ions as functions of photon energy were measured from condensed layers of varied thicknesses (100 ML, 10 ML, 1 ML on a 1 ML Xe spacer layer). Clear evidence for repulsive (or at most extremely weakly bound) core excitations for NH 3, and for bound core excitations with vibrational resolution for CH 4, has been obtained. Surface and bulk excitations can be well distinguished using the graded surface sensitivity of the two signals from the various layers. For the surface excitations, surface symmetry breaking both in terms of electronic and vibronic states has been deduced from polarization-dependent behaviour. Possible information on Rydberg and valence contents of the final states involved, and on contributions of ultrafast dissociation, are discussed.
Published Version
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