  We use first-principles calculations to uncover and explain a new type of
anomalous low-velocity stopping effect in proton-irradiated graphene. We
attribute a shoulder feature that occurs exclusively for channeling protons to
enhanced electron capture from $\sigma$+$\pi$ orbitals. Our analysis of
electron emission indicates that backward emission is more sensitive to proton
trajectory than forward emission and could thus produce higher contrast images
in ion microscopy. For slow protons, we observe a steep drop in emission,
consistent with predictions from analytical models.
