A pathway to diphosphorus from the dissociation of photoexcited tetraphosphorus

Abstract

We report a computational study of an energetically favorable pathway for the excited-state dissociation of a tetrahedral P₄ molecule into two P₂ molecules via the simultaneous breaking of four chemical bonds along a highly symmetric (D_2d) reaction pathway. Along this pathway, a degeneracy occurs between the first excited state of P₄ and the ground state of 2P₂ at a lower total energy (ca. 4.7 eV) than the initial state, indicating that the initial photoexcitation provides sufficient energy for the dissociation without significant kinetic barriers. We also found that sequential dissociation of the four P–P bonds exhibits larger activation barriers thus making this a less viable dissociation pathway. Our computational investigation uncovers complicated photochemistry in elemental phosphorus, and suggests a likely mechanism for the environmentally friendly inclusion of phosphorus atoms into organic molecules.