Density functional theory (DFT)-based molecular dynamics (DFTMD) simulations in combination with a Fourier transform of dipole moment autocorrelation function are performed to investigate the adsorption dynamics and the reaction mechanisms of self-coupling reactions of both acetylide (H3C-C(ß)=C(a)(ads)) and ethyl (H3C(ß)-C(a)H2(ads)) with I(ads) coadsorbed on the Ag(111) surface at various temperatures. In addition, the calculated infrared spectra of H3C-C(ß)=C(a)(ads) and I coadsorbed on the Ag(111) surface indicate that the active peaks of -C(ß)=C(a)- stretching are gradually merged into one peak as a result of the dominant motion of the stand-up -C-C(ß)=C(a)- axis as the temperature increases from 200 K to 400 K. However, the calculated infrared spectra of H3C(ß)-C(a)H2(ads) and I coadsorbed on the Ag(111) surface indicate that all the active peaks are not altered as the temperature increases from 100 K to 150 K because only one orientation of H3C(ß)-C(a)H2(ads) adsorbed on the Ag(111) surface has been observed. These calculated IR spectra are in a good agreement with experimental reflection absorption infrared spectroscopy results. Furthermore, the dynamics behaviors of H3C-C(ß)=C(a)(ads) and I coadsorbed on the Ag(111) surface point out the less diffusive ability of H3C-C(ß)=C(a)(ads) due to the increasing s-character of Ca leading to the stronger Ag-Ca bond in comparison with that of H3C(ß)-C(a)H2(ads) and I coadsorbed on the same surface. Finally, these DFTMD simulation results allow us to predict the energetically more favourable reaction pathways for self-coupling of both H3C-C(ß)=C(a)(ads) and H3C(ß)-C(a)H2(ads) adsorbed on the Ag(111) surface to form 2,4-hexadiyne (H3C-C=C-C=C-CH3(g)) and butane (CH3-CH2-CH2-CH3(g)), respectively. The calculated reaction energy barriers for both H3C-C=C-C=C-CH3(g) (1.34 eV) and CH3-CH2-CH2-CH3(g) (0.60 eV) are further employed with the Redhead analysis to estimate the desorption temperatures approximately at 510 K and 230 K, respectively, which are in a good agreement with the experimental low-coverage temperature programmed reaction spectroscopy measurements.
Relation:
The Journal of Chemical Physics 140(2), pp.024706(11 pages)
