Adsorption of N-2 monolayers on Papyex in the liquid and vapor phases

The nuclear resonance photon scattering (NRPS) technique has been used for measuring the out-of-plane tilt angle of physisorbed N-15(2) relative to a graphite surface (in a Papyex form) between n=0.6 and 2.4 commensurate mono layers (CML), in the range 80-297 K. This was done by measuring the resonan tly scattered intensities from the 6324 keV level in N-15 with the photon b eam parallel and perpendicular to the Papyex planes. For the first time, de tailed measurements were carried out at high temperatures, well above the 2 D tricritical point (T(c)approximate to 85 K), where the N-2 gas is known t o occur in the vapor phase on Papyex. The results show beyond any doubt tha t even at T = 140 K, the molecules have, on average, a definite forward til t with respect to the graphite surface and that the tilt angle increases wi th coverage. The results are compared with molecular dynamic simulations (M DS) and grand canonical Monte Carlo calculations (GCMC). (C) 1999 Elsevier Science B.V. All rights reserved.