Résumé
We study the formation and destruction of molecules in the ejecta of Population III supernovae (SNe) using a chemical kinetic approach to follow the evolution of molecular abundances from day 100 to day 1000 after explosion. The chemical species included in the study range from simple diatomic molecules to more complex dust precursor species. All relevant molecule formation and destruction processes that are unique to the SN environment are considered. Our work focuses on zero-metallicity progenitors with masses of 20, 170, and 270 M-circle dot, and we study the effect of different levels of heavy element mixing and the inward diffusion of hydrogen and helium on the ejecta chemistry. We show that the ejecta chemistry does not reach a steady state within the relevant timespan (similar to 3 yr) for molecule formation, thus invalidating previous results relying on this assumption. The primary species formed in the harsh SN environment are O-2, CO, SiS, and SO. The SiO, formed as early as 200 days after explosion, is rapidly depleted by the formation of silica molecular precursors in the ejecta. The rapid conversion of CO to C-2 and its thermal fractionation at temperatures above 5000 K allow for the formation of carbon chains in the oxygen-rich zone of the unmixed models, providing an important pathway for the formation of carbon dust in hot environments where the C/O ratio is less than 1. We show that the fully mixed ejecta of a 170 M-circle dot progenitor synthesizes 11.3 M-circle dot of molecules, whereas 20 M-circle dot and 270 M-circle dot progenitors produce 0.78 M-circle dot and 3.2 M-circle dot of molecules, respectively. The admixing of 10% of hydrogen into the fully mixed ejecta of the 170 M-circle dot progenitor increases its molecular yield to similar to 47 M-circle dot. The unmixed ejecta of a 170 M-circle dot progenitor SN without hydrogen penetration synthesizes similar to 37 M-circle dot of molecules, whereas its 20 M-circle dot counterpart produces similar to 1.2 M-circle dot. This smaller efficiency at forming molecules is due to the large fraction of He+ in the outer mass zone of the ejecta. Finally, we discuss the cosmological implication of molecule formation by Pop III SNe in the early universe.