Born-Oppenheimer molecular dynamics simulation of pentanoic acid adsorption on α-Al2O3

Adsorption of a single pentanoic acid (C5H10O2) molecule on (0001) α-Al2O3 in a vacuum was explored with the aid of Born-Oppenheimer molecular dynamics simulations. Computer simulations were carried out considering two different situations, namely a clean Al/O-terminated surface and, also, a (0001) α-Al2O3 surface saturated with doubly-coordinated, isolated hydroxyls. In the first case, pentanoic acid adsorbs dissociatively, with the creation of an isolated surface hydroxyl, while the oxygen from the molecule's former carbonyl makes a bond to a nearby surface Al. On the other hand, pentanoic acid adsorbs on hydroxylated alumina by making a strong hydrogen bond to a surface oxygen, with the molecule aligning itself nearly parallel to the surface after full relaxation. For each case (i.e., pentanoic acid adsorption on Al/O-terminated or hydroxylated corundum surface), the different adsorption mechanism has a marked impact on the respective calculated infrared absorption spectrum, which can be of further use as an analytical tool to determine the underlying adsorption mechanism in actual experiments.