A novel theoretical study of thermally-induced reaction and vibration dynamics of methanol dissociative adsorption onto a Si(001) surface

Abstract

The thermally-induced reaction and vibration dynamics of methanol (CH₃OH_(g)) dissociative adsorption onto a Si(001) surface have been studied by combining density functional theory (DFT)-based molecular dynamics (DFTMD) simulations with a molecular adsorption sampling scheme and a wavelet transform for investigating the reaction pathways and corresponding vibrational spectra. Based on the simulated results, CH₃OH_(g) firstly approaches the Si(001) surface to interact with the buckled-down Si atom at temperatures from 100 K to 300 K, and then the O–H bond of CH₃OH_(ads) breaks within 10 picoseconds only at 300 K due to the elongation of the O–H bond. Furthermore, the time-resolved vibrational spectrum constructed by a wavelet transform of the structural coordinate auto-correlation function (WT-SCAF) illustrates that the O–H stretching mode of CH₃OH_(ads) shifts to below 3400 cm⁻¹ when the H atom of the O–H bond is closer to the buckled-up Si atom of the adjacent dimers. This is due to the fact that the noticeable attractive force between the H atom of the O–H bond and the dangling bond at the buckled-up Si atom of the adjacent dimers prompts the O–H bond to break and then leads to both CH₃O and H species adsorbed on the buckled-down and buckled-up Si atoms, respectively.