The impact of collisional rate coefficients on molecular hyperfine selective excitation

摘要: Nuclei with non-zero spin induce hyperfine splittings in the rotational spectrum of many commonly observed interstellar molecules. Radiative transfer modelling such species requires general a good knowledge selective collisional rate coefficients. We investigate this work impact coefficients on molecular excitation. The approximate sudden and statistical (proportional) methods are first compared to almost exact recoupling approach. Rate presented for large number CN HCN transitions, para-H2(j = 0) as collider. approximation approach, which both predict propensity rule Δj ΔF, found agree within factor 3 or better. calculations then performed using velocity gradient approximation. At low moderate total optical depths (τ ≲ 10), where relative populations close weights, approximations shown provide accurate alternatives higher opacities, however, appears matter method is be significantly superior