Efficiency of energy transfer in protonated diglycine and dialanine SID: Effects of collision angle, peptide ion size, and intramolecular potential

Classical trajectory simulations are performed to study energy transfer in collisions of protonated diglycine, (gly)₂H⁺, and dialanine, (ala)₂H⁺, ions with the diamond {111} surface, for a collision energy E_i in the range of 5-110eV and incident angles of 0 and 45° with respect to the surface normal. The distribution of energy transfer to vibrational/rotational degrees of freedom, ΔE _int, and to the surface, ΔE_surf, and of energy remaining in peptide ion translation, E_f, are very similar for (gly)₂H⁺ and (ala)₂H⁺. The average percent energy transferred to ΔE_surf and E_f increases and decreases, respectively, with increase in E_i. Average energy transfer to ΔE_int is less dependent on E_i, but does decrease with increase in E_i. The AMBER and AM1 models for the (gly)₂H⁺ intramolecular potential give statistically identical energy transfer distributions in (gly)₂H ⁺+diamond {111} collisions. A comparison of the current study with previous trajectory simulations of glyH⁺, (gly)₃H ⁺, and (gly)₅H⁺ collisions with diamond {111} shows that the energy transfer efficiencies to ΔE_int, ΔE_surf, and E_f are similar for (gly) _nH⁺, n=1-5. The energy transfer distributions for (gly)₂H⁺+diamond {111} collisions depend on the collision angle and do not scale in accord with the normal component of the collision energy E_iⁿ for collisions with θ_i of 0 and 45°.