Heterogeneous Interactions between Gas-Phase Pyruvic Acid and Hydroxylated Silica Surfaces: A Combined Experimental and Theoretical Study

The adsorption of gas-phase pyruvic acid (CH3COCOOH) on hydroxylated silica particles has been investigated at 296 K using transmission Fourier transform infrared (FTIR) spectroscopy and theoretical simulations. Under dry conditions (<1% relative humidity, RH), both the trans-cis (Tc) and trans-trans (Tt) pyruvic acid conformers are observed on the surface as well as the (hydrogen bonded) pyruvic acid dimer. The detailed surface interactions were further understood through ab initio molecular dynamics simulations. Under higher relative humidity conditions (above 10% RH), adsorbed water competes for surface adsorption sites. Adsorbed water is also observed to change the relative populations …

Oberflächenladungen an der CaF 2 ‐Wasser‐Grenzfläche erlauben eine sehr schnelle intermolekulare Übertragung von Schwingungsenergie

A Microscopic Interpretation of Pump–Probe Vibrational Spectroscopy Using Ab Initio Molecular Dynamics

What happens when extra vibrational energy is added to water? Using nonequilibrium molecular dynamics simulations, also including the full electronic structure, and novel descriptors, based on projected vibrational density of states, we are able to follow the flow of excess vibrational energy from the excited stretching and bending modes. We find that the energy relaxation, mostly mediated by a stretching-stretching coupling in the first solvation shell, is highly heterogeneous and strongly depends on the local environment, where a strong hydrogen bond network can transport energy with a time scale of 200 fs, whereas a weaker network can slow down the transport by a factor 2-3.

Enhanced Acid Dissociation at the Solid/Liquid Interface

In this chapter we review some recent results from first principles molecular dynamics simulations which show how molecular properties, such as proton dissociation, can be influenced upon adsorption at a solid/liquid interface. In particular, we discuss in details the increased acidity of pyruvic acid at the quartz /water interface, which is of relevance for the chemistry of the atmosphere. Our simulations unveil the special role of the microsolvation at interface, as well as the role of the silanols in stabliziing the deprotonated form of the acid. The enhanced acidity at the hydrophilic quartz/water interface is at odd with what typically found at the water/air interface where acidity is …

Increased Acid Dissociation at the Quartz/Water Interface.

As shown by a quite significant amount of literature, acids at the water surface tend to be “less” acid, meaning that their associated form is favored over the conjugated base. What happens at the solid/liquid interface? In the case of the silica/water interface, we show how the acidity of adsorbed molecules can instead increase. Using a free energy perturbation approach in combination with electronic structure-based molecular dynamics simulations, we show how the acidity of pyruvic acid at the quartz/water interface is increased by almost two units. Such increased acidity is the result of the specific microsolvation at the interface and, in particular, of the stabilization of the deprotona…

Surface charges at the CaF2/water interface allow very fast intermolecular vibrational-energy transfer

Abstract We investigate the dynamics of water in contact with solid calcium fluoride, where at low pH, localized charges can develop upon fluorite dissolution. We use 2D surface‐specific vibrational spectroscopy to quantify the heterogeneity of the interfacial water (D2O) molecules and provide information about the sub‐picosecond vibrational‐energy‐relaxation dynamics at the buried solid/liquid interface. We find that strongly H‐bonded OD groups, with a vibrational frequency below 2500 cm−1, display very rapid spectral diffusion and vibrational relaxation; for weakly H‐bonded OD groups, above 2500 cm−1, the dynamics slows down substantially. Atomistic simulations based on electronic‐structu…