Long-range interactions in the ozone molecule: spectroscopic and dynamical points of view

Using the multipolar expansion of the electrostatic energy, we have characterized the asymptotic interactions between an oxygen atom O$(^3P)$ and an oxygen molecule O$_2(^3\Sigma_g^-)$, both in their electronic ground state. We have calculated the interaction energy induced by the permanent electric quadrupoles of O and O$_2$ and the van der Waals energy. On one hand we determined the 27 electronic potential energy surfaces including spin-orbit connected to the O$(^3P)$ + O$_2(^3\Sigma_g^-)$ dissociation limit of the O--O$_2$ complex. On the other hand we computed the potential energy curves characterizing the interaction between O$(^3P)$ and a O$_2(^3\Sigma_g^-)$ molecule in its lowest vibrational level and in a low rotational level. Such curves are found adiabatic to a good approximation, namely they are only weakly coupled to each other. These results represent a first step for modeling the spectroscopy of ozone bound levels close to the dissociation limit, as well as the low energy collisions between O and O$_2$ thus complementing the knowledge relevant for the ozone formation mechanism.Comment: Submitted to J. Chem. Phys. after revisio

The effect of reagent rotation on gas phase reactions

This dissertation examines the effect of reagent rotation in elementary gas phase reactions. Historically, the effect of rotational excitation of the reagents of a chemical reaction on the reactive cross section has been poorly understood. One of the major reasons for this was the lack of a simple model in which the dynamics could be visualized. In this work, such a model is developed and utilized in order to elucidate trends in reactivity observed upon rotational excitation. Within the context of this model, exact quantum mechanical scattering calculations are performed for a simple atom-diatom system. These exact quantum mechanical probabilities of reaction as a function of rotational quantum number, P\sp{\rm R}(j), exhibit the characteristic dip and climb behavior observed in many classical trajectory calculations. These exact P\sp{\rm R}(j) are then compared to P\sp{\rm R}(j) obtained via several approximate quantum mechanical methods, for example, the Centrifugal Sudden (CS) and the Infinite Order Sudden (IOS). We find that, in general, the CS method does a good job reproducing exact P\sp{\rm R}(j). In contrast, the IOS method only reproduces the correct qualitative trends when the collision is sudden like. The applicability of classical mechanics as it relates to rotational excitation is also investigated. Classical P\sp{\rm R}(j) obtained using the model are compared to the exact quantum mechanical P\sp{\rm R}(j). The viability of several classical mechanical approximate scattering techniques is also investigated. The classical CS approximation reproduces qualitative trends observed in the exact classical P\sp{\rm R}(j), while the classical IOS only reproduces the correct qualitative trends under sudden conditions. Having established the accuracy of classical mechanics in dealing with rotational excitation we then utilized it to fully define the phenomena responsible for the trends observed in the classical P\sp{\rm R}(j). Lastly, full 3D classical trajectories are carried out for the F + H\sb2(0,j) and OH(0,j) + H\sb2(0,j\sp\prime) reactions. The model qualitatively reproduces the trends observed in the classical reaction cross section as a function of j, S\sp{\rm R}(j), for both reactions

Quantum and quasi-classical dynamics of the C(3P) + O2(3Σ −g) → CO(1Σ+) + O(1D) reaction on its electronic ground state

The dynamics of the C((3)P) + O(2)((3)Σ(−)(g)) → CO((1)Σ(+)) + O((1)D) reaction on its electronic ground state is investigated by using time-dependent wave packet propagation (TDWP) and quasi-classical trajectory (QCT) simulations. For the moderate collision energies considered (E(c) = 0.001 to 0.4 eV, corresponding to a range from 10 K to 4600 K) the total reaction probabilities from the two different treatments of the nuclear dynamics agree very favourably. The undulations present in P(E) from the quantum mechanical treatment can be related to stabilization of the intermediate CO(2) complex with lifetimes on the 0.05 ps time scale. This is also confirmed from direct analysis of the TDWP simulations and QCT trajectories. Product diatom vibrational and rotational level resolved state-to-state reaction probabilities from TDWP and QCT simulations agree well except for the highest product vibrational states (v′ ≥ 15) and for the lowest product rotational states (j′ ≤ 10). Opening of the product vibrational level CO(v′ = 17) requires ∼0.2 eV from QCT and TDWP simulations with O(2)(j = 0) and decreases to 0.04 eV if all initial rotational states are included in the QCT analysis, compared with E(c) > 0.04 eV obtained from experiments. It is thus concluded that QCT simulations are suitable for investigating and realistically describe the C((3)P) + O(2)((3)Σ(−)(g)) → CO((1)Σ(+)) + O((1)D) reaction down to low collision energies when compared with results from a quantum mechanical treatment using TDWPs

Solvation Effects on Association Reactions in Microclusters: Classical Trajectory Study of H+Cl(Ar)n

The role of solvent effects in association reactions is studied. Classical trajectory studies of the system H + Cl(Ar)n, (n=1,12) are used to investigate the influence of size, structure and internal energy of the "microsolvation" on the H + Cl association reaction. The following effects of solvating the chlorine in an Arn cluster are found. In the H + ClAr system there is a large "third body" effect. The single solvent atom stabilizes the newly formed HCl molecule by removing some of its excess energy. The cross section found at low energies is a substantial fraction of the gas kinetic cross section. The molecule is produced in highly excited vibrational-rotational states. Some production of long-lived HCl...Ar complexes, with lifetimes of 1 ps and larger, is found for the H + ClAr collisions. Weak coupling stemming from the geometry of the cluster is the cause for long lifetimes. These resonance states decay into HCl + Ar. At low collision energies(E=10 kJ/mol) for H + Cl(Ar)12, the H + Cl association shows a sharp threshold effect with cluster temperature. For temperatures of about T=45 K the cluster is liquidlike, and the reaction probability is high. For T<40 K the cluster is solidlike, and there is no reactivity. This suggests the potential use of reactions as a signature for the meltinglike transition in clusters. At high collision energies (E=100 kJ/mol) H atoms can penetrate also the solidlike Cl(Ar)12 cluster. At this energy, the solid-liquid phase change is found not to increase the reaction probability

Investigating transition state resonances in the time domain by means of Bohmian mechanics: The F+HD reaction

In this work, we investigate the existence of transition state resonances on atom-diatom reactive collisions from a time-dependent perspective, stressing the role of quantum trajectories as a tool to analyze this phenomenon. As it is shown, when one focusses on the quantum probability current density, new dynamical information about the reactive process can be extracted. In order to detect the effects of the different rotational populations and their dynamics/coherences, we have considered a reduced two-dimensional dynamics obtained from the evolution of a full three-dimensional quantum time-dependent wave packet associated with a particular angle. This reduction procedure provides us with information about the entanglement between the radial degrees of freedom (r,R) and the angular one (\gamma), which can be considered as describing an environment. The combined approach here proposed has been applied to study the F+HD reaction, for which the FH+D product channel exhibits a resonance-mediated dynamics.Comment: 12 pages, 9 figure

Phonon and electron excitations in abstraction processes from metallic surfaces

132 p.Tesi honetan W(100) eta W(110) gainazaletan gertatzen diren H(g)+H(ads) eta N(g)+N(ads) errekonbinazio erreakzioak ikertu dira. Helburu nagusia erreakzio hauetan gertatzen diren kitzikapen elektronikoak aztertzea izan da. Hortarako, erreakzioa pausuz pausu jarraitzeko gaitasuna ematen digun dinamika kuasiklasiko deritzon metodo teorikoa erabili da. DFT bidez kalkulaturiko energia potentzial gainazaletan oinarritu dira simulazioak. LDFA eta GLO modeloak erabili dira erreakzioak metalean eragiten dituen kitzikapen elektroniko eta fononikoak ikertzeko, hurrenez hurren. Tenperaturak altuak ez direnean, errekonbinazioa Eley-Rideal (ER) edo Hot-atom (HA) deritzen mekanismoen bidez gerta liteke. Lehenengo kasuan, gas faseko (g) eta gainazaleko (ads) atomoek bat batean erreakzionatzen dute. HA mekanismoan, aldiz, gas faseko atomoa gainazalean mugitzen da denbora tarte batez erreakzionatu aurretik. Aurrekariekin bat, kitzikapen elektronikoen kontribuzioa energia galera totalari handiagoa da atomoen masa txikiagoa denenan. Kitzikapen elektronikoek, espero bezela, HA mekanismoan dute eragin gehien. Gaineztatze baxuetan gas faseko atomoen energia zinetikoa baxua denean, kitzikapen elektronikoak direla eta HA erreakzioa asko murrizten da. ER erreatibitatean eragin baxuagoa du aldiz. Dena den energia galerak esanguratsuak direla aurkitzen da mekanismo bietan. Horotara, tesi honetan errekonbinazio erreakzioen deskribapen teorikoan aurrera egin da kitzikapen elektronikoak kontutan izanez

Influence of the reactants rotational excitation on the H + D2(v = 0, j) reactivity

10 págs.; 10 figs.; 1 tab.; Special Issue: Dynamics of Molecular Collisions XXV: Fifty Years of Chemical Reaction DynamicsWe have analyzed the influence of the rotational excitation on the H + D(v = 0, j) reaction through quantum mechanical (QM) and quasiclassical trajectories (QCT) calculations at a wide range of total energies. The agreement between both types of calculations is excellent. We have found that the rotational excitation largely increases the reactivity at large values of the total energy. Such an increase cannot be attributed to a stereodynamical effect but to the existence of recrossing trajectories that become reactive as the target molecule gets rotationally excited. At low total energies, however, recrossing is not significant and the reactivity evolution is dominated by changes in the collision energy; the reactivity decreases with the collision energy as it shrinks the acceptance cone. When state-to-state results are considered, rotational excitation leads to cold products rovibrational distributions, so that most of the energy is released as recoil energy.The authors acknowledge funding by the Spanish Ministry of Science and Innovation (grant Consolider Ingenio 2010 CSD2009-00038). J.A., F.J.A. and P.G.J. acknowledge also funding by the Spanish Ministry of Economy and Competitiveness (grant CTQ2012-37404-C02), and V.J.H. acknowledges additional funding by the Spanish Ministry of Science and Innovation (FIS2013-48087-C2-1P) and by the European Research Council (ERC-2013-Syg-610256).Peer Reviewe

Dynamical Effects and Product Distributions in Simulated CN + Methane Reactions

Dynamics of collisions between structured molecular species quickly become complex as molecules become large. Reactions of methane with halogen and oxygen atoms serve as model systems for polyatomic molecule chemical dynamics, and replacing the atomic reagent with a diatomic radical affords further insights. A new, full-dimensional potential energy surface for collisions between CN + CH4 to form HCN + CH3 is developed and then used to perform quasi-classical simulations of the reaction. Coupled-cluster energies serve as input to an empirical valence bonding (EVB) model, which provides an analytical function for the surface. Efficient sampling permits simulation of velocity-map ion images and exploration of dynamics over a range of collision energies. Reaction populates HCN vibration, and energy partitioning changes with collision energy. The reaction cross-section depends on the orientation of the diatomic CN radical. A two-dimensional extension of the cone of acceptance for an atom in the line-of-centers model appropriately describes its reactivity. The simulation results foster future experiments and diatomic extensions to existing atomic models of chemical collisions and reaction dynamics.status: publishe