title: Dynamics of energy transfer and soft-landing in collisions of protonated dialanine with perfluorinated self-assembled monolayer surfaces.
abstract: Chemical dynamics simulations are reported which provide atomistic details of collisions of protonated dialanine, ala2-H(+), with a perfluorinated octanethiolate self-assembled monolayer (F-SAM) surface. The simulations are performed at collision energies Ei of 5.0, 13.5, 22.5, 30.00, and 70 eV, and incident angles 0° (normal) and 45° (grazing). Excellent agreement with experiment (J. Am. Chem. Soc., 2000, 122, 9703-9714) is found for both the average fraction and distribution of the collision energy transferred to the ala2-H(+) internal degrees of freedom. The dominant pathway for this energy transfer is to ala2-H(+) vibration, but for Ei = 5.0 eV ∼20% of the energy transfer is to ala2-H(+) rotation. Energy transfer to ala2-H(+) rotation decreases with increase in Ei and becomes negligible at high Ei. Three types of collisions are observed in the simulations: i.e. those for which ala2-H(+) (1) directly scatters off the F-SAM surface; (2) sticks/physisorbs on/in the surface, but desorbs within the 10 ps numerical integration of the simulations; and (3) remains trapped (i.e. soft-landed) on/in the surface when the simulations are terminated. Penetration of the F-SAM by ala2-H(+) is important for the latter two types of events. The trapped trajectories are expected to have relatively long residence times on the surface, since a previous molecular dynamics simulation (J. Phys. Chem. B, 2014, 118, 5577-5588) shows that thermally accommodated ala2-H(+) ions have an binding energy with the F-SAM surface of at least ∼15 kcal mol(-1).
authors.affiliation: Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061, USA. bill.hase@ttu.edu.
authors.forename: Subha
authors.initials: S
authors.lastname: Pratihar
authors.forename: Swapnil C
authors.initials: SC
authors.lastname: Kohale
authors.forename: Dhruv G
authors.initials: DG
authors.lastname: Bhakta
authors.forename: Julia
authors.initials: J
authors.lastname: Laskin
authors.forename: William L
authors.initials: WL
authors.lastname: Hase
mesh_terms: D000409:Alanine / Q000737:chemistry*; D004151:Dipeptides / Q000737:chemistry*; D004735:Energy Transfer; D005461:Fluorine / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D011522:Protons; D011789:Quantum Theory; D013499:Surface Properties
chemical_list: D004151:Dipeptides; D011522:Protons; D005461:Fluorine; D000409:Alanine