Radiative ³He(²H, γ)⁵Li capture at astrophysical energy and its role in accumulation of ⁶Li at the BBN

Big Bang Nucleosynthesis (BBN) relevance reactions ³He(²H, γ)⁵Li, ³H(³He, γ)⁶Li, and ⁵Li(n, γ)⁶Li as a key to approach for scenario of ⁶Li formation are treated. The rates of reaction for these processes are analyzed. Comparison of the reactions rates and the prevalence of light elements leads to the assumption that the two-step process ²H + ³He $\to {}^5$Li + γ and n + ⁵Li $\to {}^6$Li + γ can make a significant contribution to the formation of ⁶Li at the BBN at least at temperatures $T_9$ of the order of unity. Calculations of the total cross sections, astrophysical S-factor, and reaction rates have been performed for ³He(²H, γ)⁵Li radiative capture within the modified potential cluster model with forbidden states, which follow from the classification of the orbital cluster states according to Young diagrams. Numerical data and corresponding parametrizations cover the energy range up to 5 MeV and temperature range $T_9$ 3He(²H, γ)⁵Li are presented.