Theoretical Studies of Dissociative Recombination

We are currently investigating the dissociative recombination (DR) of electrons with the molecular ions $\mathrm{N}_2\mathrm{H}^+$ and and $\mathrm{C}_3\mathrm{H}_3^+$. These ions exist in the interstellar medium, and accurate DR rate constants are needed for astrophysical models. We are performing large scale electronic structure calculations of the excited-state potential surfaces of $\mathrm{N}_2\mathrm{H}$ necessary to treat the process $e^- + \mathrm{N}_2\mathrm{H}^+ \rightarrow \mathrm{N}_2 + \mathrm{H}$ or $\mathrm{N} + \mathrm{NH}$. The work is based on using the block diagonalization method to determine diabatic potential curves. The dissociating curve that governs DR is then easily identified, and off-diagonal coupling terms can be used to determine the autoionization width $\Gamma$ that is essential for a dynamics calculation. The status of the calculations will be presented at the conference. We have also investigated the normal modes of the molecular ion $\mathrm{C}_3\mathrm{H}_3^+$. We expect that energy flow into and out of the vibration of a single CH bond may influence the overall DR dynamics, and we account for this effect using an appropriate quantum mechanical wave function for the initial state.