Experimental and theoretical study of CO collisions with CH3- and CF3-terminated self-assembled monolayers

Abstract

We present an experimental and theoretical study of the dynamics of collisions of the CO molecule with organic surfaces. Experimentally, we scatter CO at 60 kJ mol(-1) and 30 degrees incident angle from regular (CH(3)-terminated) and omega-fluorinated (CF(3)-terminated) alkanethiol self-assembled monolayers (SAMs) and measure the time-of-flight distributions at the specular angle after collision. At a theoretical level, we carry out classical-trajectory simulations of the same scattering process using CO/SAM potential-energy surfaces derived from ab initio calculations. Agreement between measured and calculated final translational energy distributions justifies use of the calculations to examine dynamical behavior of the gas/surface system not available directly from the experiment. Calculated state-to-state energy-transfer properties indicate that the collisions are notably vibrationally adiabatic. Similarly, translational energy transfer from and to CO rotation is relatively weak. These trends are examined as a function of collision energy and incident angle to provide a deeper understanding of the factors governing state-to-state energy transfer in gas/organic-surface collisions.

Gas–surface energy exchange and thermal accommodation of CO2 and Ar in collisions with methyl, hydroxyl, and perfluorinated self-assembled monolayers

“…Under these conditions, which are identical to those reported here, the final energy is found to increase linearly to only 9 kJ mol À1 for much larger exit angles, y f = 801. 56 In addition, a similar linear dependence of final energy on exit angle has been shown in experimental and theoretical studies for Ar atom scattering from CH 3 -and F-SAMs. 33 Based on these previous results, we speculate that the general trends displayed by the data in Fig.…”

“…3 originate from a previously proposed model, discussed below, for describing CO 2 scattering from long-chain organic self-assembled monolayers. 33,49 Previous work for Ar, 30 CO, 55,56 and other rare-gas scattering [31][32][33]38 from alkanethiol SAMs shows that the average final energy depends only weakly on final scattering angle. For example, molecular dynamics simulations indicate that 60 kJ mol À1 CO, incident on a CH 3 -SAM at y i = 301, leaves the surface with an average of 6 kJ mol À1 of translational energy at the specular angle.…”

Mechanistic details of energy transfer and soft landing in ala2-H+ collisions with a F-SAM surface

“…Table 5 summarizes the results, regarding penetration and trapping, from previous simulations of projectile + organic surface collisions. 16,29,35,[64][65][66] For the first entry in Table 5, 64 the dynamics are studied versus the C 12 H-SAM inter chain 65 trapping is most important for Kr and the hE f i percent is largest for Ne. The penetration percentages for the three rare gases differ by less than a factor of two.…”

“…As shown in Table 5, the dynamics of CO and OH collisions with H-SAM and F-SAM surfaces are not strongly dependent on their vibrational and rotational quantum numbers. 16,66 For these collisions, the H-SAM surface has much more trapping, with a very small amount of penetration. For the fluorinated surface there is no penetration and energy transfer to hE f i is larger.…”

“…Self-assembled monolayers (SAMs) on metal surfaces are widely used in nanoscience and nanotechnology. 1 Experimental 2-27 and computational simulation studies [28][29][30][31][32][33][34][35][36][37][38][39][40][41] have probed the dynamics of energy transfer, 2,3,16,[18][19][20][21][22][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] surface adsorption, 18,22,[28][29][30][34][35][36]41 and thermal accommodation [4][5]…”