State-resolved photon-H$_2^+$ cross sections and rate coefficients

Studies of molecular plasmas both in local thermodynamic equilibrium (LTE) and non-LTE require state-resolved (electronic, vibrational and rotationally resolved) transition cross sections or rate coefficients to calculate populations (for non-LTE plasmas), opacities and emissivities. Here we present state-resolved results of photodissociation and radiative association of H$_2^+$ and its isotopologues (D$_2^+$, T$_2^+$, HD$^+$, HT$^+$, and DT$^+$). We note that going beyond the commonly utilized ``two-level'' approximation of H$_2^+$ could be important in models when dealing with radiation temperatures that can access photon wavelengths around 100 nm. For example at these wavelengths, and a material temperature of 8400K, the photodissociation cross section via the (second electronically excited) 2$p \pi_u$ state is over three times larger than the photodissociation cross section via the (first electronically excited) 2$p \sigma_u$ state.