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

Abstract

The nuclear resonance photon scattering (NRPS) technique has been used for measuring the out-of-plane tilt angle of physisorbed 15N 2 relative to a graphite surface (in a Papyex form) between n=0.6 and 2.4 commensurate monolayers (CML), in the range 80–297 K. This was done by measuring the resonantly scattered intensities from the 6324 keV level in 15N with the photon beam parallel and perpendicular to the Papyex planes. For the first time, detailed measurements were carried out at high temperatures, well above the 2D tricritical point ( T c≈85 K), where the N 2 gas is known to occur in the vapor phase on Papyex. The results show beyond any doubt that even at T=140 K, the molecules have, on average, a definite forward tilt with respect to the graphite surface and that the tilt angle increases with coverage. The results are compared with molecular dynamic simulations (MDS) and grand canonical Monte Carlo calculations (GCMC).