Ab initio calculations of autoionizing states using block diagonalization: Collinear diabatic states for dissociative recombination of electrons with N2H+

► We calculate dissociating, autoionizing states using block diagonalization. ► We applied the method to the dissociative recombination of electrons with N2H+. ► Rydberg-valence coupling was distentangled from N2 bond-breaking effects. ► For N2H, the N2 + H product channel appears to be favored.