Abstract

A theoretical study is reported of the mechanisms for internal rotation of hydrogen peroxide (HOOH), hydrogen thioperoxide (HSOH) and hydrogen persulphide (HSSH). Calculations at the ab initio HF//6-311G** and MP2//6-311G** levels show that these are gauche molecules presenting double-barrier torsional potentials. Important results have been obtained: two di????fferent isomerization mechanisms (trans and cis) have been characterized in terms of specific local interactions; the corresponding energy barriers have been classifed according to through bond and through space interactions; and the principle of maximum hardness is qualitatively verified in all three molecules.