1,2-Dichloroethane on Cu(100) and Oxygen-Covered Cu(100):  Conformation, Orientation, and Transformation

Abstract

Temperature-programmed reaction/desorption, reflection−absorption infrared spectroscopy, and density functional theory calculations have been employed to investigate the adsorption of ClCH2CH2Cl on Cu(100) and O/Cu(100) in the subjects of identification of the rotational isomers, adsorption energy, adsorption geometry, thermal stability of the layer structure, and transformation between the trans and gauche conformers. On Cu(100), both the trans and gauche forms of ClCH2CH2Cl coexist on the surface at a monolayer coverage, and their thermal desorption peak appears at 187 K. The trans molecules are likely adsorbed with the C−Cl bonds approximately parallel to the surface. On O/Cu(100), the gauche conformer is the predominant species and the desorption temperature is shifted to 199 K. It is found that the ClCH2CH2Cl layer structure on Cu(100), up to a ∼15 monolayer coverage studied, is stable between 120∼140 K. However, O/Cu(100) shows an interesting contrast. The thermal stability only appears at a coverage below ∼3 monolayers. The transformation from gauche to trans takes place for higher coverages. On the basis of the cluster-model calculations without consideration of the interaction between adsorbed molecules, it is shown that the activation energy for the transformation between trans and gauche ClCH2CH2Cl on O/Cu(100) is much lower than that on Cu(100), suggesting that the trans molecules are easier to be transformed into gauche ones on O/Cu(100), as they are adsorbed on the proximity of preadsorbed oxygen atoms.

Solvent Dependence on Conformational Transition, Dipole Moment, and Molecular Geometry of 1,2-Dichloroethane: Insight from Car−Parrinello Molecular Dynamics Calculations

“…This holds in particular for 1,2-dichloroethane (DCE) which is one of the simpler molecules in the series. Experimentally, the molecular geometry and population of different conformational states of DCE have been studied in its gaseous phase, condensed phase, − and in the solution phase of polar and nonpolar solvents. ,, The confinement effect on the conformational equilibrium of DCE in nanoconfined methanol has been investigated; likewise, the structure and dynamics of DCE on metal surface and protein surface have also been theoretically investigated. Moreover, there are studies investigating the pressure effect on the conformational equilibrium. , In the gaseous phase, the trans form has been reported to be more stable than the gauche form, something that has been attributed to the electrostatic energy which is more favorable when similar charges are separated by long distances.…”

“…Experimentally, the molecular geometry and population of different conformational states of DCE have been studied in its gaseous phase, 5 condensed phase, [6][7][8] and in the solution phase of polar and nonpolar solvents. 1,9,10 The confinement effect on the conformational equilibrium of DCE in nanoconfined methanol has been investigated; 11 likewise, the structure and dynamics of DCE on metal surface 12 and protein surface 13 have also been theoretically investigated. Moreover, there are studies investigating the pressure effect on the conformational equilibrium.…”

Benchmarks and Dielectric Constants for Reparametrized OPLS and Polarizable Force Field Models of Chlorinated Hydrocarbons

“…The formation of a liquid/liquid interface between water and a CHC is particularly interesting for those cases where the CHC phase can be “polarized” substantially in the vicinity of the interface by the presence of the water phase. These cases have hence drawn attention also in theoretical studies. − In particular, 1,2-dichloroethane (1,2-DCE) constitutes an interesting prototype model molecule, owing to the considerable difference in the dipole moments of its gauche and trans conformers. − Both conformers occur in a dynamic equilibrium in the liquid phase of 1,2-DCE, and the trans conformer’s dipole moment vanishes due to its inversion symmetry.…”