The Chemistry of the Early Universe

Abstract

Abstract. The chemistry of the early Universe is a fascinating field of study. Even in the absence of any elements heavier than lithium, a surprising degree of chemical complexity proves to be possible, giving the topic considerable interest in its own right. In addition, the fact that molecular hydrogen plays a key role in the formation of the first stars and galaxies means that if we want to understand the formation of these objects, we must first develop a good understanding of the chemical evolution of the gas. In this review, I first give a brief introduction to the chemistry occurring in the gas prior to the formation of the first stars and galaxies, and then go on to discuss in more detail the main chemical processes occurring during the gravitational collapse of gas from intergalactic to protostellar densities, and how these processes influence the final outcome of the collapse.

A simple model for molecular hydrogen chemistry coupled to radiation hydrodynamics

“…Grains of interstellar dust serve as catalysts by which H i sticks and coalesces into H 2 (Gould & Salpeter 1963; see Wakelam et al 2017 for a comprehensive review). H 2 may also form by gas phase interactions, but this process is much slower and was only important in the early Universe when metals were scarce (Galli & Palla 1998). At high temperatures (T 1000 K), collisions between H 2 and other particles dissociate H 2 into H i (Glover & Abel 2008).…”

State-to-State Quantum Mechanical Calculations of Rate Coefficients for the D+ + H2 → HD + H+ Reaction at Low Temperature

“…The reverse reaction HD + H + → D + + H 2 is endothermic in contrast with the title reaction, which is exothermic by 39.37 meV (456.9 K) and thus has no energy threshold. So, at low temperatures (<200 K), the HD/H 2 ratio becomes enhanced over the cosmological D/H ratio at a significantly high level by about 2 orders of magnitude. ,, The uncertainty about the rate coefficients for the D + + H 2 → HD + H + reaction directly affects model predictions for the HD abundance and thereby the cooling rate of the primordial gas. It is therefore of astrophysical importance to determine an accurate value of these rates, and helping to understand the cooling requires a complete set of the state-to-state rate coefficients as well as the total rate coefficient.…”

“…of a set of coupled second-order differential equations, which are solved using the Johnson−Manolopoulos logderivative propagator 46. In this work, for J = 0, 200 states d i s s o c i a t e a t l a r g e h y p e r -r a d i u s i n t o t h e H 2(20,18,16,14,12,10,6) rovibrational set (this notation indicates the largest rotational level j for each vibrational manifold v = 0,1,...,6) and the HD(25,23,20,18,16,14,11,8,1) rovibrational set for v′ = 0,1,...,8. So a large number of closed channels needed for convergence has been included in the present study.…”