Vibrationally inelastic processes which can occur in collisions of low-energy simple negative ions with diatomic molecules are studied by using the H--H-2 system and by applying to it the quantum treatment of the relevant multichannel scattering theory. The unusual behavior of the vibrationally inelastic cross sections, integral and differential, is linked to specific features of the lowest-lying potential-energy surface, and microscopic effects of such features on the dynamics are discussed in relation to what was found earlier for the H+-H-2 system.