Quantum defect analysis of $\rm{H_3^+}+\rm{e^-}$ system

The neutral triatomic hydrogen molecule ($\rm{H_3}$) plays an important role in astrophysics because its cation form $\rm{H_3^+}$ acts as a proton donor in chemical reactions occurring in interstellar clouds. As the simplest triatomic neutral molecule, $\rm{H_3}$ also attracts fundamental interest. Treating the system of $\rm{H_3}$ molecule as a Rydberg electron attaching to a $\rm{H_3^+}$ ion, we carry out \emph{ab initio} study of the system with quantum defect theory, improving on some approximations used in existing theory.