HIGH-RESOLUTION STUDIES OF THE FRAGMENTATION OF CONDENSED AMMONIA ANDMETHANE BY CORE EXCITATIONS USING ELECTRON AND ION EMISSION TECHNIQUES

We have analysed the core-to-bound excitations in condensed NH3 and CH 4 in the Nls and Cls regions, respectively, utilizing highly resolved synchrotron radiation. Photoabsorption (from partial electron yields) and photodesorption of H+ ions as functions of photon energy were meas ured from condensed layers of varied thicknesses (100 ML, 10 ML, I ML on a 1 ML Xe spacer layer). Clear evidence for repulsive (or at most e xtremely weakly bound) core excitations for NH3, and for bound core ex citations with vibrational resolution for CH4, has been obtained. Surf ace and bulk excitations can be well distinguished using the graded su rface sensitivity of the two signals from the various layers. For the surface excitations, surface symmetry breaking both in terms of electr onic 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.