Hyperthermal N+ ions efficiently abstract C atoms from a graphite surface to form CN- ions. An incident energy threshold of similar to0 eV for CN- emission is obtained and agrees with the exothermicity of the reaction. Both the mean and the maximum product translational energies are correlated with the incident N+ energy, excluding the Langmuir-Hinschelwood mechanism. While most CN- ions retain only similar to4% of the incident translational energy, a maximum energy transfer ratio of similar to25% from the incident ion to the product is observed, suggesting that the abstraction occurs via the Eley-Rideal mechanism. Energetic analysis of the reaction and the product reveals that the abstraction reaction occurs at carbon defect sites by breaking two rather than three C-C bonds.