Interactions of Water with Pyridine and Benzene Studied by TOF-SIMS

Fragment and cluster ions from gaseous and condensed pyridine produced under electron impact

The ion-distribution from condensed pyridine due to 2 keV electron impact shows hydrogenated fragments and clusters with m/z ≤ 320 u and shifts towards higher masses compared to the gas-phase fragmentation. The formation of a bond between the pyridine and a carbenium ion is crucial for the stability of the selected cluster ions.

Non-covalent interaction of benzene with methanol and diethyl ether solid surfaces

We have investigated the interactions involved at the interface of binary, layered ices (benzene on methanol and on diethyl ether) by means of laboratory experiments and ab initio calculations on model clusters.

Coexistence of solvated electron and benzene-centered valence anion in the negatively charged benzene-water clusters

We present a combined M06 functional calculation and ab initio molecular dynamics simulation study of an excess electron (EE) in a microhydrated aromatic complex (modeled by benzene (Bz)-water binary clusters, Bz(H(2)O)(n)). Calculated results illustrate that Bz ring and water clusters are indeed linked through the π···HO interactions in the neutral Bz(H(2)O)(n) (n = 1-8) clusters, and the size of the water cluster does not influence the nature of its interaction with the π system for the oligo-hydrated complexes. The states and the dynamics of an EE trapped in such Bz-water clusters were also determined. All of possible localized states for the EE can be roughly classified into two types: (i) single, ring-localized states (the Bz-centered valence anions) in which an EE occupies the LUMO of the complexes originating from the LUMO (π*) of the Bz ring, and the π···HO interactions are enhanced for increase of electron density of the Bz ring. In this mode, the carbon skeleton of the Bz part is significantly deformed due to increase of electron density and nonsymmetric distribution of electron density induced by the interacting H-O bonds; (ii) solvated states, in which an EE is trapped directly as a surface state by the dangling hydrogen atoms of water molecules or as a solvated state in a mixed cavity formed by Bz and water cluster. In the latter case, Bz may also participate in capturing an EE using its C-H bonds in the side edge of the aromatic ring as a part of the cavity. In general, a small water cluster is favorable to the Bz-centered valence anion state, while a large one prefers a solvated electron state. Fluctuations and rearrangement of water molecules can sufficiently modify the relative energies of the EE states to permit facile conversion from the Bz-centered to the water cluster-centered state. This indicates that aromatic Bz can be identified as a stepping stone in electron transfer and the weak π···HO interaction plays an important role as the driving force in conversion of the two states.

Interaction of benzene with amorphous solid water adsorbed on polycrystalline Ag

The interaction of benzene with polycrystalline Ag and amorphous solid water (D(2)O) deposited thereupon at 124 K was investigated. Metastable impact electron spectroscopy, Reflection-absorption infrared spectroscopy, and temperature programmed desorption were utilized to obtain information on the electronic structure and the relative contribution to the bonding properties of the aromatic molecules among themselves and with D(2)O. On Ag, the benzene molecular plane is oriented parallel to the surface in the first layer. The second layer is tilted with respect to the first one. A total work function decrease of 0.8 eV takes place during the buildup of the first two layers. On amorphous solid water, the orientational distribution of the benzene molecular planes is initially peaked at an angle parallel to the water surface. During the completion of the first adlayer a coverage-induced reorientation takes place, inducing a tilt of the benzene molecules of the first adlayer. Still larger benzene exposures appear to lead to the formation of three-dimensional benzene clusters. Films produced by codepositing benzene and D(2)O or by postdepositing D(2)O layers on benzene films display "volcano like" benzene desorption during ice crystallization.

How well can density functional methods describe hydrogen bonds to pi acceptors?

We employed four newly developed density functional theory (DFT) methods for the calculation of five pi hydrogen bonding systems, namely, H2O-C6H6, NH3-C6H6, HCl-C6H6, H2O-indole, and H2O-methylindole. We report new coupled cluster calculations for HCl-C6H6 that support the experimental results of Gotch and Zwier. Using the best available theoretical and experimental results for all five systems, our calculations show that the recently proposed MPW1B95, MPWB1K, PW6B95, and PWB6K methods give accurate energetic and geometrical predictions for pi hydrogen bonding interactions, for which B3LYP fails and PW91 is less accurate. We recommend the most recent DFT method, PWB6K, for investigating larger pi hydrogen bonded systems, such as those that occur in molecular recognition, protein folding, and crystal packing.

A temperature-programed time-of-flight secondary ion mass spectroscopy study of intermixing of amorphous ethanol and heavy-water films at 15–200 K

On the basis of time-of-flight secondary ion mass spectrometry, the intermolecular interactions of amorphous ethanol and heavy-water films have been investigated in terms of the translational molecular diffusion, hydrogen-bond reorganization, and isotope scrambling. The morphology of the ethanol film (heavy-water film) changes at 120 K (165 K), and the isotope scrambling takes place between the ethanol and heavy-water molecules above 140 K. The intermixing of the layered binary films of ethanol and heavy water is induced at 120 K as a consequence of the increased mobility of the ethanol molecules but the mixing is incomplete at the molecular level. The complete mixing occurs above 140-150 K provided that the highly mobile water molecules emerge. It is concluded that the viscous liquid phase evolves above the conventional glass-transition temperatures (97 and 136 K for ethanol and heavy water, respectively), which is followed by the drastic morphological change (120 and 165 K) as a consequence of the increased fluidity of the films.