Fundamental Interactions Program

Chemical Theory

Investigator(s)	DePristo, A.E.; Evans, J.W., Gordon, M.; Ruedenberg, K.			$349,000
Phone	515-294-9924
E-mail	depristo@ameslab.gov

One focus of this research is the theoretical description of the structure and dynamics of metal clusters. The goal is to determine the structure and energy of various clusters and to investigate the relationship between these properties and the reactivity of clusters with different gas-phase molecules. Close connection is made to the program of Riley and coworkers (at Argonne National Lab) which addresses many of the same questions via experimental measurements. First principle and semiempirical electronic structure techniques are utilized along with classical dynamics. Theoretical developments are directed toward discovery and testing of new one-electron density functional methods which would allow self-consistent electronic structure calculations on large systems. A second focus involves analysis of the kinetics and nonequilibrium structure associated with irreversible or far-from-equilibrium adsorption and catalytic reaction processes on solid surfaces. A smaller effort involves development of rigorous quantitative methods for ab-initio electronic structure calculation of PES, in particular based on multiconfiguration self-consistent field approaches. Applications are made to important catalysis-related reactions involving metal clusters and to combustion-related gas phase reactions.

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Fundamental Interactions Program

Molecular Beam Photoionization and Photodissociation Studies of Molecules, Clusters, and Radicals

Investigator(s)	Ng, C.Y.			$286,000
Phone	515-294-4225
E-mail	cyng@ameslab.gov

The goals of this program are (1) to obtain accurate thermochemical data, such as ionization energies and bond dissociation energies, for neutral polyatomic molecules, radicals, and their ions; (2) to study the photoionization and photodissociation dynamics of molecules and radicals induced by the absorption of UV and VUV photons; and (3) to investigate the reaction dynamics and mechanisms of fast radical-molecule and radical-radical reactions. One current focus is on the studies of organosulfur radicals and transition metal carbonyl compounds and their fragments. Oxidation of organosulfur compounds, which are emitted to the atmosphere due to the incomplete combustion of coal and oil, ultimately lead to the formation of SO₂ and acid rain. Previous studies indicate that the oxidation rate for organosulfur pollutants increases substantially in the presence of UV radiation. The study of the UV and VUV photochemistry of organosulfur species is relevant to the modeling of atmospheric sulfur chemistry cycles. Motivated to obtain a detailed understanding of the catalytic ability of transition metal ions, experiments have been initiated to examine systematically the energetics and reactivities of transition metal carbonyl compounds and their fragments. Recent focuses have also been expanded to include oxygen-containing hydrocarbon radicals.

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Chemistry Division

Metal Cluster Chemistry Research

Investigator(s)	Riley, S.J.; Parks, E.K.; Jellinek, J.; Knickelbein, M.B.			$1,163,000
Phone	630-252-6793
E-mail	RILEY@ANLCHM.CHM.ANL.GOV

The goal of this program is to understand how cluster structure depends on cluster size and how cluster properties depend on structure, thereby contributing to a better understanding of surface chemistry and heterogeneous catalysis. Experimental and theoretical studies of the chemical and physical properties of clusters of catalytically active transition metals are pursued. Experimentally, the reactivity of clusters with small molecules is investigated. These investigations include measurements of absolute reaction rate constants and adsorbate binding energies, and determinations of product compositions, the nature of adsorbate binding sites, and cluster geometrical structure. A complimentary experimental effort which uses various laser techniques to obtain the optical, infrared, and photoionization spectra of metal clusters and cluster-adsorbate complexes provides size-specific electronic structure and ionization potential information as well as detailed insights into cluster-adsorbate interactions. The theoretical effort involves studies of stable and metastable structural forms of clusters and interconversion between these, cluster phases and phase changes, thermal stability and fragmentation, reactive and nonreactive cluster-molecule interactions, etc. Both single-component and two-component (alloy) clusters are investigated using existing and newly-developed semiempirical potentials and ab initio approaches. The goal is to understand cluster properties and the mechanisms defining them in terms of the nature of the interatomic forces.

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Chemistry Division

Photoionization-Photoelectron Research

Investigator(s)	Ruscic, B.			$445,000
Phone	630-252-4079
E-mail	ruscic@anl.gov

This program focuses on the investigation of gas-phase species using the photoionization mass-spectrometric method and its derivatives (TPES, PEPICO, ZEKE, MATI). The technical capabilities of this program are being currently complemented by the addition of pulsed laser-based experiments. The scientific emphasis is on reactive intermediates in combustion and other energy-producing processes, and on key species involved in subsequent atmospheric chemistry. These ephemeral species are produced in situ using selected techniques (abstraction reactions, discharges, on-line synthesis, pyrolysis, laser photodissociation, etc.) The primary motivation of our research is to provide accurate and reliable thermochemical data and spectroscopic and structural details that are crucial in comprehending pertinent chemical reactions. In addition to detailed data, we seek to extract useful generalities, which yield new insights into the nature of chemical bonds or dynamical processes accompanying photoionization. The desired level of details is unraveled by combining suitable experimental techniques with subsequent data analysis using novel fitting methods. Our current measurements on CF₃OH, CF₂O, and CF₃-containing species address important open questions regarding the environmental soundness of the latest generation of refrigerants. Other recent measurements, such as those on C₂H₅O and CH₃O isomers, CH_nS (n=1-3), and HNCX and NCX, (X=O, S) have provided valuable new data related to combustion of hydrocarbons, alcohols, and sulfur-containing fuels, and to the industrially important RAPRENO_x process. Our experimental results also play a very important role in testing the most sophisticated ab initio calculations, which have demonstrated near-chemical accuracy for small molecules, but have not yet established a clear track record for larger (>3 nonhydrogen atoms) systems.

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Chemistry Division

Chemical Dynamics in the Gas Phase

Investigator(s)	Wagner, A.; Davis, M.; Harding, L.; Shepard, R.; MacDonald, R.; Michael, J.; Hessler, J.; Gray, S.			$2,417,000
Phone	630-252-3597
E-mail	wagner@tcg.anl.gov

The program mission is to characterize the gas-phase chemical reactivity of small molecules and radicals, especially those involved in combustion, by a combination of both theory and experiment. The experimental effort involves high-temperature reaction rate studies by UV absorption in two shock tubes and low-temperature product distribution studies by IR absorption in a flow tube. A companion data analysis effort has expanded the use of sensitivity coefficients and error propagation in accounting for secondary chemistry. Recent measurements have included the dissociation rate constants of chlorofluorocarbons (CFCs) and their alternates, the HCN product distributions from CN attack on alkanes, and the reactions of methyl radicals with themselves and with oxygen. The theoretical effort involves large-scale studies to compliment the above measurements and others done outside the group. Associated methods development emphasizes the efficient exploitation of advanced computers, especially massively parallel ones. Recent theoretical activity has included electronic structure studies of potential energy surfaces, classical and quantum dynamics studies of reactivity on those surfaces, hierarchical studies for the assignment of highly excited spectra, and low dimensional manifold studies for the simplification of coupled kinetic equations. The close coupling between theory and experiment brings a unique combination of expertise to bear on problems of chemical reactivity.

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Department of Applied Science

Combustion Kinetics and Reaction Pathways

Investigator(s)	Klemm, R.B.; Sutherland, J.W.			$550,000
Phone	516-344-4022
E-mail	klemm1@bnlux1.bnl.gov

The mission objectives of this basic research project are to improve the understanding of combustion kinetics and thermodynamics. Specific interest is focused on: (1) determining absolute rate coefficients for gas phase reactions and identifying pathways for multichannel reactions; and (2) characterizing the photoionization properties and thermochemistry of relevant molecules and free radicals. For kinetics studies, the project features a shock tube to obtain reliable kinetic measurements over a wide range in temperature (800K to 2500K). Also, theoretical calculations are performed in conjunction with experiments on the unimolecular dissociation of combustion-related molecules. For thermodynamics and reaction pathways studies, a discharge flow-photoionization mass spectrometer apparatus is employed in determining primary products from multichannel reactions and in performing photoionization studies on reactants, free radicals and stable reaction products. In addition to its intrinsic scientific interest, this work provides fundamental information to other researchers such as theorists (who need reliable experimental data with which to test their calculations) and modellers (who require rate constants and thermodynamic values in order to study practical problems like fuel efficiency, pollutant formation and destruction, flame suppression and waste chemical incineration).

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Chemistry Department

Gas-Phase Molecular Dynamics

Investigator(s)	Muckerman, J.T.; Sears, T.J.; Hall, G.E.; Preses, J.M.			$1,490,000
Phone	516-344-4368
E-mail	muckerm1@bnl.gov

Research in this program explores the energetics, dynamics and chemical reactions resulting from molecular collisions in the gas phase. We are interested in the microscopic factors affecting the structure, dynamics and reactivity of short-lived intermediates in gas-phase chemical reactions important in combustion chemistry. Molecular species are studied using both experimental and theoretical tools including high-resolution spectroscopic probes, quantal wavepacket propagation, and time-independent quantal calculations. A new initiative in radical-radical chemical reaction kinetics is being started to augment these studies. The goal of the work is a fundamental understanding of the transient species involved in chemical processes related to combustion chemistry.

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Chemistry Department

Photoinduced Molecular Dynamics

Investigator(s)	White, M.; DiMauro, L.; Beuhler, R.J.			$1,010,000
Phone	516-344-4345
E-mail	white@dynamics.chm.bnl.gov

The general aims of this program are the detailed study of molecular photofragmentation dynamics and the characterization of the structure, spectroscopy and intramolecular dynamics of chemical intermediates important in combustion chemistry. Coherent VUV and ultra-fast laser sources are used to induce photo-processes such as ionization, dissociation, intramolecular motion and desorption, the dynamics of which are probed by a variety of state- and energy-resolved ionization-based techniques and nonlinear pump-probe spectroscopy. State-resolved dissociation and photoionization measurements focus on the partitioning of energy and angular momentum in elementary photofragmentation processes at low and very high laser intensities. The latter investigate the response of molecules to intense fields well beyond the perturbative regime which introduces new selectivity and field induced fragmentation pathways. Further studies of the effects of well characterized fields on simple, isolated systems are also under investigation with the ultimate goal of optimal control of physical and chemical processes. State-resolved, VUV detection methods are also being implemented in new studies of photoinduced desorption and reactions of molecules on surfaces. These studies are focused on elucidating the mechanism of photoinduced processes via measurements of the quantum state and energy distributions of the desorbed molecules and/or molecular fragments. Other studies utilize in-situ, time-resolved, sum frequency generation spectroscopy for probing the structure and dynamics of surfaces.

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Chemical Sciences Division

Energy Transfer and Structural Studies of Molecules on Surfaces

Investigator(s)	Harris, C.B.			$233,000
Phone	510-642-2814
E-mail	CBHarris@lbl.gov

The goal of this research is to study the dynamics of excited electronic states on surfaces, at interfaces, and in condensed phases and to develop new laser techniques for studying these dynamics. The research program is both theoretical and experimental in character, and includes nonlinear optical and ultrafast laser techniques in addition to a variety of standard surface science tools for characterizing surfaces and adsorbate-surface interactions. Recent work has centered on developing and applying femtosecond two-photon photoemission to study the dynamics of electrons at metal-polymer and magnetic interfaces. The ultrathin layers under study range from 4 Å to 4 nm in thickness. The results of this program have a direct bearing on high-speed technological devices and materials, the fundamental physics of two-dimensional systems, and on other problems of general interest such as surface photochemistry and optical processes at interfaces.

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Chemical Sciences Division

Chemical Dynamics

Investigator(s)	Lee, Y.T.; Chen, Y.; Head-Gordon, M.; Lester, W.A.; Miller, W.H.; Moore, C.B.; Neumark, D.; Johnston, H.S.; Suits, A.G.			$2,187,000
Phone	510-486-4754
E-mail	AGSuits@lbl.gov

The objectives of this program are to develop the basic knowledge and understanding of the mechanisms and dynamics of elementary chemical reactions that have a major impact on combustion and advanced energy production technologies. Recent emphasis has been to determine the structure and chemical behavior of reactive free radicals and highly-excited polyatomic molecules, and to provide microscopic details of primary dissociation and bimolecular processes. These objectives are achieved with a strongly coupled experimental and theoretical-computational approach, using emerging technologies. Dynamical studies use advanced molecular beam and laser methods including photofragmentation translational spectroscopy, ion imaging and fast-beam photodissociation techniques. Kinetics studies employ IR laser flash kinetic spectroscopy, IR-UV double resonance and high-resolution UV-VUV laser spectroscopy. New theoretical methods and models are developed both to provide insight into chemical reactivity and the dynamics of reactive processes, and to provide more accurate and efficient means of calculating reaction rates and molecular structures. Current studies include crossed-beam reaction dynamics and photochemistry with emphasis on processes involving reactive hydrocarbon radicals and carbon atoms. Studies continue to probe the structure and dynamics of the chemical transition state and the microscopic mechanisms of primary chemical processes. New studies take advantage of the Chemical Dynamics Beamline recently commissioned at the Advanced Light Source, providing greatly enhanced experimental capability for studies of primary photochemical and photoionization processes and reaction dynamics.

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Chemical Sciences Division

Physical Chemistry with Emphasis on Thermodynamic Properties

Investigator(s)	Pitzer, K.S.			$80,000
Phone	510-642-3472
E-mail	KSPitzer@lbl.gov

The object of this project is the measurement and the theoretical calculation of the thermodynamic and related properties of novel or prototype systems. Recently, the emphasis has been on ionic fluids under near-critical or supercritical conditions. Binary fluids have been selected and measured that model a pure ionic fluid but have critical points at experimentally accessible temperatures. Critical exponents have been determined by phase equilibria and light scattering methods. Recent results show a clear crossover from Ising to classical (mean field) exponents as the temperature moves away from the critical point. Other recent research has included comprehensive equations of state for the important systems such as NaOH-H₂O and CaCl₂-H₂O. For the latter, new theoretical basis was developed based on mixtures of dipole (H₂O) and quadrupole (CaCl₂) molecules for which Monte Carlo calculations were made. This represented a good first approximation that was refined by small semi-empirical adjustment terms. Investigations often involve collaboration with Lawrence Livermore National Laboratory (LLNL), Oak Ridge National Laboratory (ORNL), or the United States Geological Survey (USGS).

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Energy and Environment Division

Combustion Chemistry

Investigator(s)	Brown, N.J.			$205,000
Phone	510-486-4241
E-mail	NJBrown@lbl.gov

Combustion processes are governed by chemical kinetics, energy transfer, transport, fluid mechanics, and the complex interactions among these. The pathways for energy movement and the competition among the pathways determines reaction rates, product yields, and product state energy distributions. Understanding the fundamental chemical processes offers the possibility of optimizing combustion processes. The objective of our research is to address fundamental issues of chemical reactivity in combustion systems. We emphasize studying chemistry at both the microscopic and macroscopic levels. Our current activities are concerned with 1) developing models of combustion process with complex (realistic) flow fields that include detailed chemical mechanisms; 2) developing tools to establish limits of model validity; 3) using functional sensitivity analysis to explore relationships between dynamic observables and the potential energy surface structure that are important in rate coefficient calculations; and 4) calculating rate coefficients. A theme of our research is to bring new advances in computing, and, in particular, parallel computing to the study of important, and computationally intensive combustion problems.

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Division of Applied Physics

Chemical Kinetics Modeling

Investigator(s)	Westbrook, C.K.			$40,000
Phone	510-422-4108
E-mail	westbrook1@llnl.gov

This project emphasizes numerical modeling of chemical kinetics of combustion. Combustion modeling applications in both practical combustion systems and in controlled laboratory experiments are included. Elementary reaction rate parameters are combined into mechanisms, which then describe reaction of the fuels being studied. Detailed sensitivity analyses are used to identify those reaction rates and product species distributions to which the results are most sensitive and therefore warrant the greatest attention from other experimental and theoretical research programs. Experimental data from a variety of environments validate the reaction mechanisms, including results from laminar flames, shock tubes, flow systems, detonations, and even internal combustion engines. Particular attention will be given to chemical factors including fuel molecular size and structure, emphasizing differences in combustion of isomers of selected hydrocarbons.

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Environmental Molecular Sciences Laboratory

Chemical Structure and Dynamics

Investigator(s)	Colson, S.D.			$2,425,000
Phone	509-375-6882
E-mail	sd_colson@pnl.gov

The Chemical Structure and Dynamics program responds to the need for a fundamental molecular-level understanding of chemistry at environmental interfaces, by providing insight into condensed-phase chemistry and developing and validating ab-initio theories. There are three primary program elements: (1) Interfacial Chemistry, with a special focus on water-oxide interfaces; (2) High-Energy Processes at Environmental Interfaces; and (3) Understanding the Condensed Phase Through Cluster Models, recognizing atomic and molecular clusters as a form of matter whose properties lie outside the realm of general chemical experimental science, and that not only provide a quantitative basis for comparison with theory, but are also the source of a microscopic understanding of the condensed phase. The approach includes (1) synthesis of unique and well-characterized surfaces and interfaces by controlled deposition of atoms, molecules, and clusters using molecular-beam epitaxy; (2) characterization of surfaces and interfaces by atomic-resolution surface mapping (e.g., scanning tunneling microscopy) and near-field optical microscopy, in addition to various state-of-the-art surface science and optical spectroscopic methods combined with molecular scattering and diffusion studies; (3) synthesis of atomic and molecular clusters that mimic the structures of surface sites and of solvated species in solutions and at interfaces; (4) laser methods for studying atoms and molecules with time resolution sufficient to measure chemical dynamics in real time; and (5) direct photon and/or electron excitation of surfaces, interfaces, and molecules to model chemical processes important in mixed waste storage (radiolysis) and in the energetic destruction of wastes.

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Environmental Molecular Sciences Laboratory

Molecular Theory and Modeling

Investigator(s)	Dunning, T.H.; Garrett, B.C.; Corrales, L.R.; Dang, L.X.; Feller, D.F.; McCarthy, M.I.; Palmer, B.J.; Peterson, K.A.			$2,425,000
Phone	509-375-6863
E-mail	th_dunning@pnl.gov

The molecular theory and modeling project is designed to increase understanding of molecular processes important in environmental chemistry. The project integrates ab initio studies of fundamental molecular processes in model systems (e.g., clusters) with modeling of the complex molecular systems found in the environment. Four research areas are emphasized: (1) properties (e.g., structure and energetics) of aqueous clusters and aqueous solutions containing inorganic species (e.g., metal and radionuclide ions) and organic species (e.g., chlorinated hydrocarbons, CHCs), including the studies of molecular processes at aqueous-vapor and liquid-liquid interfaces (e.g., water-CHC interfaces); (2) structure and energetics of ion-ligand complexes (such as metal ions with crown ethers) and the dynamics of complex formation in aqueous solutions, including studies of factors influencing selectivity and efficiency (e.g., ligand design, solvation, etc.); (3) properties of aqueous-mineral interfaces that control the binding of ions and molecules to soil minerals and the dynamics of molecular processes at these interfaces, including adsorbate kinetics and solvent and adsorbate structure at the interface; (4) properties of amorphous materials that control their dissolution (e.g., by water) and degradation (e.g., by radiolysis), including the structure and thermodynamics of bulk materials, surfaces, and interfaces with other phases. This knowledge will further the development of new processes for the separation of metals from liquid wastes, the construction of reliable models of contaminant transport and transformation in soils and groundwater, and the assessment of amorphous materials proposed for long term isolation of radionuclides.

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Combustion Research Facility

Turbulent Reacting Flow Research

Investigator(s)	Barlow, R.S.; Schefer, R.W.; Paul, P.H.; Chen, J.H.; Najm, H.N.			$1,300,000
Phone	510-294-2688
E-mail	barlow@sandia.gov

This experimental and computational research project is directed toward an increased understanding of the coupling between chemical kinetics and turbulent mixing in reacting flows. Current research efforts address fundamental issues, such as the effects of differential diffusion; unsteady strain and flame curvature; the influence of heat release on the scalar dissipation field in nonpremixed flames; the geometric properties of turbulent premixed flames; and the role of turbulence-chemistry interactions in the formation of pollutants. Quantitative techniques for simultaneous imaging of multiple scalars are used to determine the spatial structure of turbulent reaction zones. The temporal evolution of flame structures is investigated by obtaining two co-planar images of CH with a variable time delay. The influence of turbulent mixing on thermochemical states is determined by simultaneous point measurements of NO, OH, the major species, temperature, and mixture fraction. These detailed multiscalar data reveal instantaneous relationships among scalars and constitute a unique basis for evaluation and refinement of turbulent combustion models. Fundamental aspects of reacting flow are studied computationally by direct numerical simulation, where all scales of fluid motion are computed. Two-dimensional flow simulations with detailed chemical kinetic mechanisms are used to investigate hydrocarbon flame response to unsteady flow-induced strain rate and curvature. Recent focus has included migration to massively parallel architectures, adaptive mesh refinement, and stiff time-integration techniques to enhance computational efficiency.

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Combustion Research Facility

Enhanced Research Capabilities in Chemical Dynamics Research

Investigator(s)	Chandler, D.W.			$255,000 Equipment
Phone	510-294-3132
E-mail	chandler@ca.sandia.gov

A new user facility in the Combustion Research Facility at Sandia National Laboratories is being built for the study of individual reactions and processes that are important to combustion. This facility includes a crossed molecular-beam apparatus, a molecular-beam / ion-imaging apparatus and a set of tunable, high-intensity lasers. Unimolecular dissociation of small molecules will be studied to determine bond strengths, branching ratios and dissociation mechanisms. The measurement of vector correlations between fragments will be of particular interest. Collisional energy transfer processes will be studied in order to determine the amount of energy transferred between a hot polyatomic molecule and cold "bath" molecules. These bath molecules will typically be atoms or diatomic molecules. Bimolecular reactions such as the H + O₂ and H + CO₂ reaction will also be studied using the unique crossed molecular-beam apparatus incorporating ion-imaging techniques for the detection of the reaction products. This technique utilizes narrow band lasers and spatially resolved ion detection to determine the velocity and quantum state of the ions formed. This information provides a stringent test of potential energy surfaces that dictate the reaction kinetics.

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Combustion Research Facility

Chemical Dynamics and Kinetics

Investigator(s)	Chandler, D.W.; Miller, J.A.; Rohlfing, E.A.; Hayden, C.C.; Taatjes, C.A.			$1,750,000
Phone	510-294-3132
E-mail	chandler@ca.sandia.gov

The goal of this research is to understand the details of fundamental chemical processes that occur in combustion. Experiments in chemical kinetics use approaches such as laser-photolysis/laser-induced fluorescence, long-path IR absorption, mass spectrometric and laser diagnosed flow-reactor studies, and high-temperature shock-tube measurements. Recent systems of interest have included the reactive systems CH + CO, O₂ and Cl + hydrocarbons and the collisional quenching of electronically excited OH. These experimental studies are aided by quantum chemical and statistical theoretical calculations. Experiments in chemical dynamics emphasize collecting data for elementary processes and individual molecules resolved to a quantum-state level. Techniques utilized include ion imaging of unimolecular and bimolecular reactions, femtosecond time-resolved approaches (transient absorption, photoelectron spectroscopy, and stimulated Raman scattering), and linear and nonlinear laser spectroscopies. Recent applications have included ion-imaging studies of the product angular distributions of the H atom fragments and H₂ fragments from the multiphoton excitation of methane. Femtosecond time-resolved studies using photoelectron spectroscopy have focused on the investigation of internal conversion dynamics in conjugated polyenes. Recent spectroscopic studies have emphasized the application and development of two-color resonant four-wave mixing and laser-induced grating techniques for molecular spectroscopy and photodissociation dynamics, with application to the important HCO and CH₂CHO radicals.

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Combustion Research Facility

Novel Laser Facility for Basic Research in Optical Diagnostics

Investigator(s)	Farrow, R.L.; Paul, P.H.			$50,000 Operating $370,000 Equipment
Phone	510-294-3259
E-mail	farrow@sandia.gov

It has become clear that continued progress in developing quantitative optical diagnostics requires an increasingly rigorous and detailed understanding of collisional phenomena. We propose to construct an innovative system of high-repetition rate, short-pulse lasers optimized for excite/probe studies of collisional processes. The lasers will be highly configurable with respect to pulse widths and output wavelengths, and will offer near-transform-limited pulse widths in the range 10-100 ps and at ~2 ns. This system will allow us to 1) significantly extend our previous RET experiments over a wider range of temperatures, to more subject species, and to foreign-gas colliders; 2) measure mass transport properties, energy transfer, and reorienting collisions in transient species using novel laser-induced grating techniques; 3) measure electronic quenching rates of species with short upper-state lifetimes; and 4) develop new picosecond-pulse diagnostic techniques that are less sensitive to collisional effects than conventional methods. These capabilities will have a significant impact on the advancement of optical diagnostic techniques such as CARS, LIF, degenerate four-wave mixing (DFWM) and absorption spectroscopy, through enhanced understanding of collisional processes, leading to more quantitative diagnostics modeling. The availability of sub-nanosecond pulses will allow basic studies to be conducted under combustion-like conditions. In addition, the lasers will provide powerful new capabilities when applied directly as diagnostics tools. The system will be located in a dedicated laboratory available for collaborative experiments by external users and CRF staff. External researchers will benefit from the facility in two ways: through improved diagnostics codes and scientific publications available from the CRF, and through use of the equipment during visits. Interested researchers should consult the section on CRF user facilities elsewhere in this document.

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Combustion Research Facility

Combustion Research Facility (CRF) Diagnostics Research: Nonlinear Spectroscopic Processes

Investigator(s)	Farrow, R.L.; Rakestraw, D.J.			$550,000
Phone	510-294-3259
E-mail	farrow@sandia.gov

This project involves the development, support, and application of nonlinear spectroscopic diagnostics for Combustion Research Facility programs. Emphasis is on coherent anti-Stokes Raman spectroscopy (CARS), resonant four-wave mixing techniques, and cavity ringdown spectroscopy for measurements in reacting gases. CARS is a relatively mature technique that provides spatially and temporally precise measurements of temperature and major species concentrations. Degenerate four-wave mixing (DFWM) has recently emerged as a coherent diagnostic roughly similar to CARS but offering greatly increased sensitivity. Cavity ringdown spectroscopy is a laser absorption technique that provides greatly enhanced sensitivity compared to conventional methods. The work is focused on investigations of fundamental issues involved in quantitative applications of DFWM. Topics include experimental studies of isolated DFWM line shapes and intensities as influenced by collisional and Doppler broadening, electronic quenching, predissociation, thermal-grating generation, and laser saturation effects. High-resolution pulsed laser systems, in both the ultraviolet (UV) and infrared (IR) wavelength regions, are used for detailed spectral studies. The experimental results are compared to theoretical calculations, leading to quantitative but simpler models for spectral analysis software. Computer codes for analyzing CARS and DFWM spectra are being developed and made available to diagnostics and combustion researchers. Polyatomic molecules in flames and discharges have been detected by exciting IR transitions using DFWM and cavity ringdown techniques. The use of IR excitation here is new, and will dramatically increase the number of species detectable by these methods. A technique for measuring the methyl radical, a transient polyatomic species important in combustion and diamond film growth, has been developed based on DFWM with UV excitation. Current work is aimed at further quantifying a method of detecting carbon monoxide by multiphoton-excited laser-induced fluorescence (LIF). Ionization and two-photon cross sections are being investigated to provide a more accurate model for analyzing LIF data for carbon monoxide concentration measurements.

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Combustion Research Facility

Flame Chemistry: Modeling and Experiments

Investigator(s)	Miller, J.A.; Rakestraw, D.J.			$900,000
Phone	510-294-2759
E-mail	jamille@ca.sandia.gov

This research program represents an integrated effort to understand the chemistry of combustion both qualitatively and quantitatively through the development of predictive mathematical models. There are three aspects of the program: (1) the mathematical modeling of flame experiments and other macroscopic experiments where chemistry is a critical factor, (2) the theoretical prediction of rate coefficients and product distributions of critical elementary reactions using a combination of statistical and dynamical methods in conjunction with ab initio potential energy surfaces, and (3) low-pressure flame experiments in which laser-induced florescence and mass spectrometry are the principal diagnostic tools. The focus of the research is on combustion-generated pollutants (nitrogen oxides, soot and its precursors, and other air toxics) and on limit phenomena in combustion (flammability limits, extinction limits, etc.)

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Combustion Research Facility

Combustion Research Facility (CRF) Diagnostics Research: Novel Techniques and Strategies

Investigator(s)	Trebino, R.; Paul, P.H.			$550,000
Phone	510-294-2893
E-mail	trebino@sandia.gov

The research goals of this project include the conception and development of novel laser-based diagnostic techniques for Combustion Research Facility programs. New techniques involving ultrafast phenomena, wave-mixing, and thermo-acoustic scattering as well as new strategies in planar laser-induced fluorescence (PLIF) and resonant multiphoton excitation are being actively pursued. Frequency-resolved optical gating techniques provide full characterization of single ultrashort laser pulses. These new capabilities and recently developed ultrashort-pulse lasers are being exploited further to develop transient absorption and time-domain resonant wave-mixing combustion diagnostics for measurements of temperature, pressure, and relative concentrations. Investigations of thermo-acoustic scattering processes, exposed in degenerate four-wave-mixing research, are being pursued for potential application as diagnostics of velocity, viscosity, temperature, and concentration. Time-resolved PLIF for quantitative two-dimensional measurements are limited by low signal strengths and a strong sensitivity to quenching processes. Studies of collisional energy transfer and quenching processes are leading to predictive models of quenching cross sections for molecules such as NO and OH. Results from these and other fundamental studies, combined with new laser or camera technologies, are providing new capabilities to combustion researchers.

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