Kenneth D. Jordan

Theoretical study of the (H2O)6 cluster

Abstract MP2 calculations are performed on selected structures of (H2O)6. A prism-like structure is predicted to be lowest in energy, but three other structures are found to lie energetically within 0.3 kcal/mol of this structure. The S6 hexagonal structure is predicted to lie 0.5–1.0 kcal/mol higher in energy.

Theoretical modeling of the OH stretch infrared spectrum of carboxylic acid dimers based on first-principles anharmonic couplings

Carboxylic acid dimers serve as prototypical systems for modeling the unusual spectral behavior of the hydride stretch fundamental. Large anharmonic effects associated with the pair of cooperatively strengthened OH⋯O=C hydrogen bonds produces complicated infrared spectra in which the OH stretch oscillator strength is spread over hundreds of wave numbers, resulting in a complicated band sub-structure. In this work cubic anharmonic constants are computed along internal coordinates associated with the intramolecular OH stretch, intermolecular stretch, and OH bend internal coordinates for the formic acid and benzoic acid dimers. These are then projected onto the normal coordinates to produce mixed states that are used in computing the OH stretch infrared spectrum. For the benzoic acid dimer the calculations accurately reproduce for three deuterated isotopomers the overall breadth and much of the vibrational sub-structure in the observed spectra. For the formic acid dimer, the spectrum is calculated using a mo...

Monte Carlo simulation of (H2O)8 : evidence for a low-energy S4 structure and characterization of the solid ↔ liquid transition

It is found that (H2O)8 possesses two nearly isoenergetic structures, one with D2d and the other with S4 symmetry, and that the (H2O)8 cluster undergoes a transition between a ‘‘solidlike’’ phase (dominated by the S4 and D2d structures) and ‘‘liquidlike’’ phase at a temperature near 119 K.

Ultrafast Interfacial Proton-Coupled Electron Transfer

The coupling of electron and nuclear motions in ultrafast charge transfer at molecule-semiconductor interfaces is central to many phenomena, including catalysis, photocatalysis, and molecular electronics. By using femtosecond laser excitation, we transferred electrons from a rutile titanium dioxide (110) surface into a CH3OH overlayer state that is 2.3 ± 0.2 electron volts above the Fermi level. The redistributed charge was stabilized within 30 femtoseconds by the inertial motion of substrate ions (polaron formation) and, more slowly, by adsorbate molecules (solvation). According to a pronounced deuterium isotope effect (CH3OD), this motion of heavy atoms transforms the reverse charge transfer from a purely electronic process (nonadiabatic) to a correlated response of electrons and protons.

Understanding the sensor response of metal-decorated carbon nanotubes

We have explored the room temperature response of metal nanoparticle decorated single-walled carbon nanotubes (NP-SWNTs) using a combination of electrical transport, optical spectroscopy, and electronic structure calculations. We have found that upon the electrochemical growth of Au NPs on SWNTs, there is a transfer of electron density from the SWNT to the NP species, and that adsorption of CO molecules on the NP surface is accompanied by transfer of electronic density back into the SWNT. Moreover, the electronic structure calculations indicate dramatic variations in the charge density at the NP-SWNT interface, which supports our previous observation that interfacial potential barriers dominate the electrical behavior of NP-SWNT systems.

High resolution S1←S0 fluoescence excitation spectra of the 1‐ and 2‐hydroxynaphthalenes. Distinguishing the cis and trans rotamers

Both fluorescence excitation and dispersed emission techniques have been used to study the S1←S0 electronic spectra of 1‐ and 2‐hydroxynaphthalene (1/2HN) in the collision‐free environments of a supersonic jet and a twice‐skimmed molecular beam, using both pulsed and high‐resolution cw lasers operating in the ultraviolet. In the jet experiments, we observe that each molecule exhibits two electronic origins, separated by 274 cm−1 in 1HN and by 317 cm−1 in 2HN. In the beam experiments, we resolve the rotational structure of each of the four bands and determine the inertial constants of all eight zero‐point vibrational levels, accurate to ±0.1 MHz. We also determine the orientations of the four optical transition moments in the molecular frame. Significant differences in both the inertial constants and the transition moment orientations are observed in each band. Similar experiments have been performed on the hydroxy‐deuterated 1/2HN (1/2DN).A comparison of the results obtained for 1/2DN with those for the c...

Temporary negative ions in the chloromethanes CHCl2F and CCl2F2: Characterization of the σ* orbitals

The electron transmission spectra of chlorometers CHCl2F and CCl2F2 are presented. The electron affinities are evaluted compared with thoses calculated using self‐consistent field methods. (AIP)

Use of the histogram and jump‐walking methods for overcoming slow barrier crossing behavior in Monte Carlo simulations: Applications to the phase transitions in the (Ar)13 and (H2O)8 clusters

The histogram and jump‐walking algorithms are combined to deal efficiently with the problem of slow barrier crossing in Monte Carlo simulations. The utility of the histogram/jump‐walking scheme is illustrated by application to the (Ar)13 and (H2O)8 clusters in their ‘‘phase transition’’ regions. Slow barrier crossing behavior is particularly acute for (H2O)8 as modeled by the TIP3P potential. Even in this case, the histogram/jump‐walking algorithm proves to be quite successful at attaining equilibrium.

A second generation distributed point polarizable water model.

A distributed point polarizable model (DPP2) for water, with explicit terms for charge penetration, induction, and charge transfer, is introduced. The DPP2 model accurately describes the interaction energies in small and large water clusters and also gives an average internal energy per molecule and radial distribution functions of liquid water in good agreement with experiment. A key to the success of the model is its accurate description of the individual terms in the n-body expansion of the interaction energies.

Infrared spectroscopy of negatively charged water clusters: Evidence for a linear network

We report autodetachment spectra of the mass-selected, anionic water clusters, (H2O)n−, n=2, 3, 5–9, 11 in the OH stretching region (3000–4000 cm−1), and interpret the spectra with the aid of ab initio calculations. For n⩾5, the spectra are structured and are generally dominated by an intense doublet, split by about 100 cm−1, which gradually shifts toward lower energy with increasing cluster size. This behavior indicates that the n=5–11 clusters share a common structural motif. The strong bands appear in the frequency region usually associated with single-donor vibrations of water molecules embedded in extended networks, and theoretical calculations indicate that the observed spectra are consistent with linear “chainlike” (H2O)n− species. We test this assignment by recording the spectral pattern of the cooled (argon solvated) HDO⋅(D2O)5− isotopomer over the entire OH stretching frequency range.