Dynamics of selective molecular excitation - Laser photocatalysis of bromine reactions

Tuned ruby laser for photocatalysis of reaction between excited bromine molecules and fluorocarbon

Oxidation of dimethyl-ether and ethylene in the atmosphere and combustion environment and thermodynamic studies on hydrofluorocarbons using ab initio calculation methods

Reaction pathways and kinetics are analyzed on CH3OC·H2 unimolecular decay and on the complete CH3OC·H2 + O2 reaction system using thermodynamic properties (ΔHf°298, S°298, and C(T) 300≤T/K≤1500) derived by two ab initio calculation methods, CBS-q and G2. These are used to determine thermodynamic properties of reactants, intermediate radicals and transition state (TS) compounds. Quantum Rice-Ramsperger-Kassel (QRRK) analysis is used to calculate energy dependent rate constants, k(E), and master equation is used to account for collisional stabilization. Comparison of calculated fall-off with experiment indicates that the CBS-q and G2 calculated Ea,rxn for the rate controlling transition state (-scission reaction to C·H2O + C·H2OOH) needs to be lowered by factor of 3.3 kcal/mol and 4.0 kcal/mol respectively in order to match the data of Sehested et al. Experimental results on dimethyl-ether pyrolysis and oxidation reaction systems are compared with a detailed reaction mechanism model. The computer code CHEMKIN II is used for numerical integration. Overall agreement of the model data with experimental data is very good. Reaction pathways are analyzed and kinetics are determined on formation and reactions of the adduct resulting from OH addition to ethylene using the above ab initio methods. Hydrogen atom tunneling is included by use of Eckart formalism. Rate constants are compared with experimentally determined product branching ratios (C·H2CH2OH stabilization : CH2O + CH3 : CH3CHO + H). ab initio calculations are performed to estimate thermodynamic properties of nine fluorinated ethane compounds (fluoroethane to hexafluoroethane), eight fluoropropane (1-fluoropropane, 1,1- and 1,2-difluoropropane, 1,1,1- and 1,1,2-trifluoropropane, 1,1,1,2- and 1,1,2,2-tetrafluoropropane and 1,1,2,2-pentafluoropropane), and 2- fluoro,2-methylpropane. Standard entropies and heat capacities are calculated using the rigid-rotor-harmonic-oscillator approximation with direct integration over energy levels of the intramolecular rotation potential energy curve. Enthalpies of formation are estimated using G2MP2 total energies and isodesmic reactions. Thermodynamic properties for fluorinated carbon groups C/C/F/H2, C/C/F2/H, C/C/F3, C/C2/F/H, C/C2/F2 and C/C3/F for fluorinated alkane compounds, CD/F/H and CD/F2 for fluorinated alkene compounds and CT/F for fluorinated alkyne compounds are estimated. Fluorine-fluorine interaction terms F/F, 2F/F, 3F/F, 2F/2F, 3F/2F and 3F/3F for alkane compounds, F//F, 2F//F and 2F/2F for alkene compounds, and F///F for alkyne compound are also estimated

Studies of negative ions formed by low energy electron impact

In this thesis the processes responsible for the formation of negative ions by the interaction of low energy electrons (0 to 15eV) with molecules in the gas phase have been investigated. Particular attention has been paid to the processes known as associative resonance capture and dissociative resonance capture. For a molecule AB, associative resonance capture is described by the equation AB + e → AB⁻, where the metastable molecular negative ion AB⁻ is formed by the capture of slow electrons. Dissociative resonance capture, described by the equation AB⁻ → A⁻ + B, results in the formation of a stable negative ion and can occur throughout the energy range studied. A historical review of the theoretical approach to electron-attachment is followed by detailed accounts of the most recent theoretical treatments of associative and dissociative resonance capture. The time-of-flight mass spectrometer used for this study has been described in some detail as have the experimental procedures developed. The various devices used to overcome the problems created by the broad electron energy distribution, which is due to the use of thermionically emitted electron beams, have been critically reviewed and the analytical deconvolution procedure adopted in this study has been described in detail. Autodetachment lifetimes and capture cross-sections for the associative attachment of electrons by several groups of organic and inorganic molecules have been measured and comparisons made with the predictions of the statistical theory for associative electron capture. Attempts to calculate electron affinities from this theory, using the lifetimes and cross -sections measured, met with some success for simple molecules and enabled conclusions to be made concerning the adequacy and limitations of the theoretical treatment. From studies of the electron energy dependence of negative ion formation for several groups of inorganic and organic molecules, various ionisation processes have been identified. Deconvolution of the ionisation curves has enabled accurate appearance potential data to be determined and, in many cases, allowed bond dissociation energies, electron affinities and heats of formation of various species to be evaluated

The kinetics of cycloaddition by fluoroolefins

Imperial Users onl

Assessment of effects on vegetation of degradation products from alternative fluorocarbons

Concern with the effects of fluorides on plants has been devoted to that resulting from dry deposition (mainly with reference to gaseous HF and secondarily with particulate forms). The occurrence of precipitation as rain or mist and the presence of dew or free water on the foliage has mainly been considered with respect to their effects on the accumulation of air-borne fluoride and not with fluoride in wet deposition. That is, precipitation has been viewed primarily with respect to its facilitation of the solution and subsequent absorption of deposits by the foliar tissues or its elution of deposited fluoride from foliage. Accordingly, our evaluation of inorganic fluoride from fluorocarbon degradation rests upon a comparison with what is known about the effects of industrial emissions and what could be considered the natural condition

Positron-molecule interactions: resonant attachment, annihilation, and bound states

This article presents an overview of current understanding of the interaction of low-energy positrons with molecules with emphasis on resonances, positron attachment and annihilation. Annihilation rates measured as a function of positron energy reveal the presence of vibrational Feshbach resonances (VFR) for many polyatomic molecules. These resonances lead to strong enhancement of the annihilation rates. They also provide evidence that positrons bind to many molecular species. A quantitative theory of VFR-mediated attachment to small molecules is presented. It is tested successfully for selected molecules (e.g., methyl halides and methanol) where all modes couple to the positron continuum. Combination and overtone resonances are observed and their role is elucidated. In larger molecules, annihilation rates from VFR far exceed those explicable on the basis of single-mode resonances. These enhancements increase rapidly with the number of vibrational degrees of freedom. While the details are as yet unclear, intramolecular vibrational energy redistribution to states that do not couple directly to the positron continuum appears to be responsible for these enhanced annihilation rates. Downshifts of the VFR from the vibrational mode energies have provided binding energies for thirty species. Their dependence upon molecular parameters and their relationship to positron-atom and positron-molecule binding energy calculations are discussed. Feshbach resonances and positron binding to molecules are compared with the analogous electron-molecule (negative ion) cases. The relationship of VFR-mediated annihilation to other phenomena such as Doppler-broadening of the gamma-ray annihilation spectra, annihilation of thermalized positrons in gases, and annihilation-induced fragmentation of molecules is discussed.Comment: 50 pages, 40 figure

Solvation Properites of Supercritical Carbon Dioxide Using Chirped-Pulse Fourier-Transform Microwave Spectra of Carbon Dioxide / 1, 1-Difluoroethene (DFE) Mixtures

Supercritical carbon dioxide (sc-C02) is a highly utilized industrial substance identified as an excellent solvent and a surfactant, which is cheaper and less hazardous than other typical solvents. The higher solubility of fluorinated hydrocarbons than their hydrocarbon (HC) analogs is not well understood and the theory behind the microsolvation of sc-C02 cannot be fully explained with the existing chemical information. Microwave spectroscopy is a good method of identifying the structural arrangement of clusters made from fluorinated HCs and C02. I n this project, microwave scans of the four different mixtures of 1 , 1-difluoroethene (DFE) and C02 were studied and additionally a pure DFE scan was studied additionally. A chirped-pulse Fourier-transform (FTMW) microwave spectrometer was used to obtain the scans. The DFE and C02 clusters can be easily identified using microwave spectroscopy because DFE is a very polar molecule and C02 has an induced dipole moment respectively. The relative intensities of the peaks in the scans and the rotational constants were considered to identify the molecular clusters. Previously identified DFE I C02 dimer structures were helpful to predict the bigger structures manually. Apart from that, the ABCluster application was used to predict the bigger structures, as guessing stable structures in three dimensions becomes harder as the cluster becomes bigger. All the predicted and approximated structures were optimized using Gaussian09W. One spectrum was identified in the DFE I C02 scans, and after comparing the intensities and rotational constants, it was confirmed as a DFE I (C02)3 tetramer. In this structure, one C02 is located above the DFE plane, another C02 is located side of DFE and the other C02 is located top-above of the DFE. One spectrum was identified in pure DFE scan and it was confirmed as a (DFE)3 trimer. In that structure, two DFEs are facing each other invertedly and the third DFE is located above the first two DFEs. This study aims to identify the salvation shell C02 makes around DFE when it dissolves. Hence, the maximum number of C02 molecules binding to a DFE molecule needs to be identified. A parallel study is occurring with vinyl fluoride (VF) I C02 and these studies collectively provide information about the variation in the number of C02 molecules that bind as the number of fluorine atoms attached to the same HC analog is varied. In the future, MathCAD applications will be used to identify largely spaced fingerprint patterns to find other stable clusters present in the experiment. Also, 13C isotopic studies will be done to confirm and compare the identified current structures

Molecular Modeling Applied to CO2-Soluble Molecules and Confined Fluids

CO2 is known to be an environmentally benign solvent. However, its feeble solvent power inhibits its wide use in industrial applications.The ultimate goal of this research is to design and optimize polymers that are highly soluble in CO2. Molecular modeling methods have been usedto analyze the results from experiments and make predictions. We have employed ab initio quantum mechanical methods to investigate interactions between CO2 molecules and polymers. This is done by computing the interactions between CO2 and polymer moieties and important functional groups. These functional groups include ether oxygens, carbonyl oxygens, and fluorines. We have identified several factors that believed to be responsible for CO2-philicity. These factors include multiple site bindings, acidic hydrogens,and geometric considerations. We have designed three possible CO2-soluble molecules based on our calculation results. Our experimental colleagues have synthesized and tested the corresponding polymers to compare with our predictions. Single wall carbon nanotubes have attracted significant scientific interest as adsorption media since their discovery. Fluids confined in nanotubes have significantly different behavior from bulk fluids. We have performed simulations for alkanes adsorbed in the internal and externalsites of carbon nanotubes. The simulation resultsqualitively match the experimental data from temperature programmed desorption. The diffusion coefficients in bulk and confined phases have been calculated. We have also studied the structure andinfrared spectra of water adsorbed in nanotubes over a wide range of temperatures. Our simulation studies have identified the essential physics responsible for a distinctive infrared band observed in recent experiments

The Use of Absolute Vibrational Band Intensities in Structural Analysis. I. n-Alkanes and Derived Ketones

A systematic investigation of group absorption band intensities in tetrachloromethane of n-alkanes and methyl n-alkyl ketones is described. Contributions to the total intensity in given regions from each structural group are established and the results used to predict the spectral intensities of methyl cyclohexane, din-hexyl ketone and cycloheptanone. The variations in CH2 and CH3 group contributions arising from proximity to· the. carbonyl are discussed in relation to the constancy of King\u27s effective atomic charge Raman group frequencies and intensities of the CH3S and CH3CH2S are established. It appears likely.that Raman band intensities, though less easily measured, could also be useful in structural analysis