Abstract
Metastable nitrogen molecules $\chem{N_{2}^*}$ (A ^{3}\Sigma^{+}_\ab{u}$) passing through a $\chem{Si_{3}N_{4}}$ nano-slit grating (slit width: 50$\un{nm}$) experience elastic and various inelastic processes, due to diagonal and off-diagonal interactions with the solid surface at short and intermediate distances (10-$100a_{0}$), i.e. mainly interactions of the van der Waals (vW) type. These processes are observed by use of a velocity selected beam and a time-of-flight analysis combined with angular measurements of scattered metastable molecules. The main feature is the occurrence of an inelastic exothermal process identified, by both its kinetic energy gain and angular dependence, as being a vibrational transition with $\Delta v=-1$. A semi-classical model using a calculated (vW) dispersion energy depending on the orientation of the molecule and the vibrational coordinate is proposed.