Showing papers in "International Reviews in Physical Chemistry in 2004"
TL;DR: In this paper, a joint computational and experimental effort was directed towards the understanding of large solid water clusters, which included structure optimizations and calculations of OH stretch spectra for select sizes in the range n = 20 − 931.
Abstract: A joint computational and experimental effort was directed towards the understanding of large solid water clusters. The computations included structure optimizations and calculations of OH stretch spectra for select sizes in the range n = 20–931. The measurements focused predominantly on OH stretch spectroscopy as a function of mean cluster size. FTIR spectra are discussed for the size range of tens to hundreds-of-thousands of molecules. Photofragment spectroscopy in molecular beams is shown to be a sensitive probe of the outer cluster surfaces. The crucial element of the different experimental approaches is the control and the estimation of the mean cluster sizes. The combined experimental and computational results are consistent with the physical picture of quasi-spherical nanocrystals with disordered reconstructed surface layers. The surface reconstruction can be viewed as the outcome of recombination of surface dangling atoms, to increase the number of hydrogen bonds. The hydrogen bonds within the mos...
203 citations
TL;DR: In this paper, it was shown that the dynamics and rates of chemical reactions at metal surfaces may be strongly influenced by electronically non-adiabatic coupling, which implies that the Born-Oppenheimer approximation may not accurately reflect the nature of transition-state traversal in reactions of catalytic importance.
Abstract: When neutral molecules with low levels of vibrational excitation collide at metal surfaces, vibrational coupling to electron-hole pairs (EHPs) is not thought to be strong unless incidence energies are high. However, there is accumulating evidence that coupling of large-amplitude molecular vibration to metallic electron degrees of freedom can be much stronger even at the lowest accessible incidence energies. As reaching a chemical transition-state also involves large-amplitude vibrational motion, we pose the basic question: are electronically non-adiabatic couplings important at transition states of reactions at metal surfaces? We have indirect evidence in at least one example that the dynamics and rates of chemical reactions at metal surfaces may be strongly influenced by electronically non-adiabatic coupling. This implies that theoretical approaches relying on the Born–Oppenheimer approximation (BOA) may not accurately reflect the nature of transition-state traversal in reactions of catalytic importance....
151 citations
TL;DR: In particular, the extent of HCl rotational excitation from reactions of Cl atoms with the functionalized organic molecules is much greater than the very cold rotational distribution as mentioned in this paper.
Abstract: Chlorine atoms react with a variety of organic molecules by abstraction of an H atom, making HCl and a radical co-product, and investigations of these reactions provide a large and valuable body of data for improved fundamental understanding of the mechanisms of reactions involving polyatomic molecules. The kinetics and dynamics of reactions of Cl atoms with alkanes have been extensively studied both by experimental and computational methods, and the key outcomes and conclusions are reviewed. These reactions serve as benchmarks for the interpretation of recent experimental data on the dynamics of reactions of Cl atoms with heteroatom functionalized organic molecules such as alcohols, ethers, amines, alkyl halides and thiols. Although bearing many similarities to the dynamics of the alkane reactions, significant differences are found: in particular, the extent of HCl rotational excitation from reactions of Cl atoms with the functionalized molecules is much greater than the very cold rotational distribution...
97 citations
TL;DR: In this paper, the optical properties of dendrimer-metal nanocomposites as well as functionalized DMMN composites are described. But the focus of this review is to describe the properties of DMMNs.
Abstract: The use of novel nanostructured materials for optical applications continues to be an important issue for the creation of new devices. New materials including metal nanoparticles have played an important role for applications in photonics, biology, as well as medicine. This review primarily concerns the use of one particular metal nanoparticle topology, dendrimer–metal nanocomposites. The focus of this review is to describe the optical properties of dendrimer–metal nanocomposites as well as functionalized dendrimer–metal nanocomposites. The description of various synthetic methodologies to produce transition metal (Au, Ag, Pd, Pt, and Cu) dendrimer nanocomposites as well as lanthanide ion-cored dendrimers are presented in this review, with further details regarding the basic characterization of these systems. The experimental procedures of the optical measurements used to probe the steady-state and time-resolved dynamics in these novel nanoparticle architectures are provided. Analysis of optical propertie...
78 citations
TL;DR: In this article, the most recent methods for studying molecular Rydberg states using high-resolution spectroscopy and theory, including effects of electric fields, are described, and the applications reviewed here include: ZEKE (zero kinetic energy), MATI (mass-analyzed threshold ionization) a...
Abstract: Molecules in high Rydberg states, in which one electron has been excited into a hydrogenic orbital of large mean radius, have many unusual properties compared to ground state molecules. These properties, which are reviewed in this article, make them suitable for a diverse and growing number of applications in chemical dynamics. The most recent methods for studying molecular Rydberg states using high-resolution spectroscopy and theory, including effects of electric fields, are described here. An important feature is the high susceptibility of Rydberg states to external field perturbation which not only has a profound effect on the observable energy levels, spectroscopic intensities and lifetimes, but is also useful for state-selective detection through field ionization. The large dipole moment that can be created in a field is also useful for controlling the motion of molecules in Rydberg states. The applications reviewed here include: ZEKE (zero kinetic energy), MATI (mass-analyzed threshold ionization) a...
63 citations
TL;DR: In this paper, a review of recent theoretical studies aimed at understanding gas/surface and gas-phase collisions at hyperthermal energies is presented, and particular attention is given to the interactions of ground-state atomic oxygen (O(3P)) with hydrocarbons.
Abstract: We review recent theoretical studies aimed at understanding gas/surface and gas-phase collisions at hyperthermal energies. The review is restricted to interactions between neutral species, and particular attention is given to the interactions of hyperthermal ground-state atomic oxygen (O(3P)) with hydrocarbons. Quantum mechanical and molecular dynamics calculations are used to simulate collisions of O(3P) with gas-phase methane, ethane, and propane molecules and with condensed-phase alkanethiolate self-assembled monolayers. The results of such studies are examined in the light of atomic-oxygen degradation of polymeric materials in low Earth orbit (LEO).
59 citations
TL;DR: In this article, the electronic spectroscopy and dissociation dynamics of transition metal cations M+ and metal oxide cations MO+ were studied using photofragment spectrograms.
Abstract: Transition metal cations M+ and metal oxide cations MO+ can activate C–H and C–C bonds in hydrocarbons. In this review, we discuss our studies of the electronic spectroscopy and dissociation dynamics of the intermediates, reactants and products of these reactions using photofragment spectroscopy. Results are presented on the spectroscopy of the intermediates of methane activation by FeO+, as well as on the spectroscopy of FeO+, NiO+ and PtO+. Resonance enhanced photodissociation allows us to measure the electronic spectroscopy of FeO+ below the dissociation limit with rotational resolution. Complementary time-dependent B3LYP calculations of excited electronic states of FeO+ and NiO+ are in surprisingly good agreement with experiment. Dissociation onsets give upper limits to bond strengths for Fe , Co , Ni , Ta and Au . These results are compared to thermodynamic measurements, and the extent to which rotational energy contributes to dissociation is investigated. The spectroscopy of the π-bonded complexes P...
54 citations
TL;DR: A review of the current status of observing these quantum bottleneck states in both bimolecular and unimolecular reactions is provided in this article, providing an updated picture of the concept of quantum bottleneck state in chemical reactions.
Abstract: The concept of quantum bottleneck states near reaction barriers is essential to the elucidation of chemical reaction rates and reaction dynamics. recent studies of the dynamics of simple gas-phase chemical reactions have revealed that the transition state controls the detailed observable characteristics of a reaction to a far greater degree than was generally imagined. however, observation of such quantum bottleneck states is extremely difficult. in this article, we provide a review of the current status of observing these quantum bottleneck states in both bimolecular and unimolecular reactions, providing an updated picture of the concept of quantum bottleneck states in chemical reactions.
49 citations
TL;DR: Some of the recent developments in the quantum dynamical studies at the conical intersections of molecular potential energy surfaces is briefly reviewed in this article, with particular emphasis given to a variety of molecular processes studied by us.
Abstract: Some of the recent developments in the quantum dynamical studies at the conical intersections of molecular potential energy surfaces is briefly reviewed in this article Particular emphasis is given to a variety of molecular processes studied by us in the recent past The non-adiabatic effects due both to the electronic as well as relativistic spin–orbit coupling are considered The discussions include the Jahn–Teller effect (and also the pseudo-Jahn–Teller effect whenever applicable) in the Rydberg emission spectrum of triatomic hydrogen and the photoelectron spectrum of cyclopropane and methyl fluoride, probing the conical intersections in ClO2 and the reagent van der Waals well in the Cl(2 P)+H2 reaction via the photodetachment spectroscopy of the negative ions, ClO and ClH , respectively, and the thermal scattering dynamics of H+H2 and Cl(2 P)+H2 reactions on multisheeted potential energy surfaces
45 citations
TL;DR: In this paper, the photofragment translational energy distribution and dissociation rate of each dissociation channel were recorded under collisionless conditions and the data were discussed with reference to the ab initio potential energy surface and statistical theory results.
Abstract: An overview is presented of our recent experimental studies of aromatic molecules using multimass ion imaging techniques. Photodissociation of benzene, fluorobenzene, toluene, m-xylene, ethylbenzene, propylbenzene and chlorotoluene at 248 nm or 193 nm was investigated under collisionless conditions. The photofragment translational energy distribution and dissociation rate of each dissociation channel were recorded. New isomerization and dissociation channels were observed from these studies. The data are discussed with reference to the ab initio potential energy surface and statistical theory results.
38 citations
TL;DR: In this paper, a review describes recent progress in ab initio calculations and modeling of weak pre-reactive van der Waals complexes that appear in the entrance channels of benchmark atom-diatom reactions.
Abstract: This review describes recent progress in ab initio calculations and modeling of weak pre-reactive van der Waals complexes that appear in the entrance channels of benchmark atom–diatom reactions. Examples from recent work are used to demonstrate how relevant potential energy surfaces are obtained and modeled from first principles. The paradigm complexes include the X(2P)–HX and X(2P)–H2 (X = F, Cl, Br) systems, with O(3P)–HCl included for comparison. In these complexes an interaction with either the HX or the H2 molecule splits a degenerate P state of an open-shell atom into three potential energy surfaces, two of which are of the same symmetry. Application of state-of-the art highly correlated methods, CCSD(T) and MRCI, to the evaluation of adiabatic and diabatic states is discussed. Nonadiabatic coupling involving potential surfaces is compared for a number of complexes. Computational modeling of this term and its relationship to electrostatic interaction are also described. Spin–orbit coupling is shown ...
TL;DR: In this article, the use of monomer properties to improve supermolecule calculations of intermolecular potentials is reviewed, and it is shown that the second-order dispersion energy is the main source of the inaccuracy.
Abstract: The use of monomer properties to improve supermolecule calculations of intermolecular potentials is reviewed. For Van der Waals dimers, the MP2 supermolecule method is too inaccurate for most purposes, and the CCSD(T) supermolecule method requires too much computer time for large molecules. Using perturbation theory to analyse the MP2 supermolecule energy shows that the second-order dispersion energy is the main source of the inaccuracy. It is shown that the dispersion energy can be improved by using more accurate dispersion energy coefficients which can be obtained from monomer frequency-dependent polarizabilities. The supermolecule MP2 electrostatic and exchange-repulsion interaction energies can also be recalculated or scaled to a higher level of theory, using monomer charge densities. Applying these corrections to the MP2 supermolecule energy does not require much additional computer time, and gives potential energy surfaces with comparable accuracy to supermolecule CCSD(T) calculations. Possible exte...
TL;DR: In this article, the effect of H2O on the electron-driven chemistry of condensed halogenated compounds is discussed, and the potential implications of this work range from environmental remediation of toxic compounds to atmospheric ozone depletion.
Abstract: The focus of this review is the effect of H2O on the electron-driven chemistry of condensed halogenated compounds. We present data with emphasis on results from the authors’ laboratories for halomethanes (CF2Cl2, CCl4, CH3I, CDCl3, CD2Cl2) and SF6. The halogenated species are suspended in or adsorbed on the surface of ultrathin films of amorphous solid water (ice) condensed on metal surfaces. Bombardment of the film by X-rays or energetic electrons leads to the release of low-energy secondary electrons; these are responsible for much of the rich electron-driven chemistry, which includes molecular decomposition, desorption of charged and neutral fragments, radical formation, anion solvation, and condensed-phase reactions. Potential implications of this work range from environmental remediation of toxic compounds to atmospheric ozone depletion.