Classical trajectory simulations are performed to study energy transfer in collisions of protonated diglycine, gly 2 -H + , and dialanine, ala 2 -H + , ions with a fluorinated octanethiol self-assembled monolayer (F-SAM) surface for collision energies E i in the range of 5-70 eV and incident angles θ i of 0 and 45°with respect to the surface normal. Both explicit-atom (EA) and united-atom (UA) models were used to represent the F-SAM surface. The simulations show the distribution of energy transfer to the peptide-ion's internal degrees of freedom, ∆E int , to the surface, ∆E surf , and in peptide-ion translation, E f , are very similar for gly 2 -H + , and ala 2 -H + . The average percentage energy transferred to ∆E surf and E f increases and decreases, respectively, with an increase in E i , while the average percentage energy transfer to ∆E int is nearly independent of E i . Changing θ i from 0 to 45°decreases and increases the percentage of energy transfer to ∆E surf and E f , respectively, but has little change in the transfer to ∆E int . Average percentage energy transfer to the surface is found to approximately depend on E i according to exp(-b/E i ). Comparisons with previous simulations show that peptide-H + collisions with the EA F-SAM model transfer approximately a factor of 2 more energy to ∆E int than do collisions with the hydrogenated SAM, that is, H-SAM. Replacing the mass of the F atoms by that of a H atom in the simulations, without changing the potential, shows that the different ∆E int energy transfer efficiencies for the F-SAM and H-SAM surfaces is a mass effect. The simulations for ala 2 -H + colliding with the EA F-SAM surface give P(∆E int ) distributions in good agreement with previous experiments and an average transfer to ∆E int of 15% as compared with the experimental value of 21%. The UA F-SAM model gives energy transfer efficiencies in qualitative agreement with those of the EA model, but there are important quantitative differences.