Flint Athena R, Fortenberry Ryan C
Department of Chemistry and Biochemistry, University of Mississippi, University, Mississippi 38677, United States.
J Phys Chem A. 2024 Oct 24;128(42):9263-9274. doi: 10.1021/acs.jpca.4c05680. Epub 2024 Oct 14.
Silicate grains comprise a large fraction of cosmic dust, motivating a need to understand how they form. The current body of work on silicates generally reflects the abundance of silicate grains, yet models for their formation often do not consider silicate chemistry on the smallest scale, which can form species available for dust grain nucleation processes. In order to expand upon previous attempts to bridge this gap in silicate chemistry, novel gas-phase reaction pathways for the magnesium silicate monomers enstatite (MgSiO) and forsterite (MgSiO) from MgH, HO, and SiO are presently computed using highly accurate quantum chemical calculations. MgSiO and MgSiO form through a series of reactions that initially excludes silicon addition, creating the elusive species MgOH and MgO prior to further reaction. The formation of the two silicate monomers is expected to be efficient with the primary bottleneck being the amount of MgH available for reaction. The addition of these reactions to cosmic chemical networks will add further clarity to the processes that govern dust formation, most significantly for those occurring within stellar outflows of asymptotic giant branch stars.
硅酸盐颗粒在宇宙尘埃中占很大比例，这促使人们需要了解它们是如何形成的。目前关于硅酸盐的研究工作总体上反映了硅酸盐颗粒的丰度，但其形成模型往往没有考虑最小尺度上的硅酸盐化学，而这种化学能形成可用于尘埃颗粒成核过程的物种。为了扩展之前弥合硅酸盐化学这一差距的尝试，目前使用高精度量子化学计算来计算由MgH、HO和SiO生成硅酸镁单体顽火辉石（MgSiO）和镁橄榄石（MgSiO）的新型气相反应途径。MgSiO和MgSiO通过一系列反应形成，这些反应最初不包括硅的添加，在进一步反应之前会生成难以捉摸的物种MgOH和MgO。预计这两种硅酸盐单体的形成效率较高，主要瓶颈在于可用于反应的MgH的量。将这些反应添加到宇宙化学网络中将进一步阐明控制尘埃形成的过程，对于在渐近巨星分支恒星的恒星外流中发生的过程尤为重要。
