Physisorption and ortho–para conversion of molecular hydrogen on solid surfaces

Ortho–para-H2conversion processes in astrophysical media

“…The OPR of H 2 formed on cold (< 50 K) solid surfaces was studied in several recent experiments and the measured values were indeed found to be consistent with the high temperature limit of 3 (see [3] and references therein). In the electronic ground state, the rotational levels of o-H 2 have odd values of the angular momentum j while the levels of p-H 2 have even j values.…”

“…Surprisingly, however, the specific OPC process has not been the object of many theoretical investigations in the past. Finally, for the conversion on solid surface, we refer the reader to the very recent review by Fukutani and Sugimoto [3]. These triatomic systems are indeed amenable to state-of-the-art computational methods and various measurements have confirmed that theory and experiment have now converged for such elementary reactions, as discussed below.…”

Adsorption of molecular hydrogen on coronene with a new potential energy surface

“…Thus, the mobility of H on defective graphene was treated in an attempt to understand the molecular hydrogen formation catalysis 7 . Graphite represents one of the best examples of inert surface to host both the formation of H 2 8-13 and its ortho-para conversion 14 . As opposed to chemical dissociative processes, physical adsorption energy is typically in the meV regime and therefore the overall mechanism becomes relevant at low temperatures [13][14][15] .…”

“…Graphite represents one of the best examples of inert surface to host both the formation of H 2 8-13 and its ortho-para conversion 14 . As opposed to chemical dissociative processes, physical adsorption energy is typically in the meV regime and therefore the overall mechanism becomes relevant at low temperatures [13][14][15] . Physisorption on PAHs can be directly considered, on the other hand, as a model to study hydrogen storage 16,17 .…”

Collective effects in physisorbed molecular hydrogen onNi/Au(111)

“…The height of the ensembles decreases to zero at 11 K. It is remarkable that during the heating ramp the H 2 ensembles occupy the same fixed area and do not change shape, but decrease in apparent height. The static boundary during heating is of particular interest because H 2 is known to desorb in UHV around 17 K, [8,24] and typically the diffusion barrier for an isolated molecule is approximately 12% that of the binding energy. [36] Most significantly, the slow and continuous decrease in apparent height is a clear deviation from classical solid two-dimensional layer desorption, which would begin from the edges inwards with the feature height remaining constant.…”