OH A2Σ Research Articles

A detailed kinetic submechanism for OH[formula omitted] chemiluminescence in hydrogen combustion revisited. Part 2

In this series of two papers, we present a novel physically sound kinetic submechanism aimed at modeling the formation and decay of chemiluminescent (electronically excited) OH∗ molecules in the ignition and combustion of hydrogen and hydrogen-based mixtures over a wide range of temperatures and pressures. The present Part describes the construction of this detailed reaction submechanism based on the groundwork and findings of the preceding paper. In so doing, we relied both on critical evaluation of known and at times conflicting experimental and theoretical data on the elementary reaction kinetics of OH∗ and on our quantum chemical calculations and rate constant estimates for the key processes. The kinetic model under development was validated against the representative dataset of the observed OH(A2Σ+→X2Π) chemiluminescent emission accompanying the high-temperature (post-shock) oxidation of various H2-containing mixtures. To improve its performance against the collected OH∗ emission data, the rate constants of some reactive and quenching processes, to which the OH∗ kinetics is the most sensitive and for which there is a particular uncertainty, were jointly varied within the limits imposed by theoretical considerations and/or the scatter in the available experimental evidence. Thus, by refining the rate constants of these elementary processes, we obtained a reasonable reaction submechanism for OH∗ that describes the known experimental data better than previous models.Novelty and significance statement Although ultraviolet OH∗ chemiluminescence as an optical signature of the combustion process and the underlying chemistry is known to provide unique capabilities for combustion diagnostics, the development of the detailed reaction mechanisms intended for quantitative interpretation of the OH∗ emission measurements has now almost stagnated. Indeed, existing kinetic models contain a discouragingly small number of elementary processes and, apparently, do not account for the full variety of possible reaction pathways of OH∗ formation and depletion. Therefore, in this serial work, we have intended to revise the current ideas about the kinetics of OH∗ production and consumption during ignition and combustion and focused first on the OH∗ kinetics in a reacting H2/O2/Ar/N2 mixture. The principal outcome of this Part of the series is a new physically based kinetic submechanism aimed at modeling the formation and decay of electronically excited OH∗ molecules in the ignition and combustion of hydrogen and hydrogen-containing mixtures. Its incorporation into any conventional kinetic model of hydrogen oxidation enables quantitative interpretation of the OH(A2Σ+−X2Π) chemiluminescent emission observed experimentally in flames and shock-heated reacting flows with an accuracy higher than that of previous analogous mechanisms. No less importantly, the rate constant approximations for a number of individual elementary processes with OH∗, recommended here based on the critical review of literature data and on our quantum chemical calculations, are also of independent interest for the kinetics of electronically excited OH∗ particles. Finally, the OH∗ reaction subset we suggested for hydrogen flames can form the basis of more complex OH∗ chemiluminescence modeling reaction mechanisms for other fuels and fuel compositions.

Influence of the argon admixture on the reactive oxide species formation inside an atmospheric pressure oxygen plasma jet

In this work, a new atmospheric pressure plasma generated in a wire-to-multiwire dielectric barrier discharge on pure oxygen is introduced. This special geometry of 13 wires (one central wire and 12 ones on the external tube) is feeding by a radio frequency (RF) power (13.56 MHz, 1 kW) and produces a stable discharge. The capacity of this device to produce oxygen reactive species and the influence of Ar gas mixture (1–3%) on this production are investigated. The main characteristics of this DBD plasma are measured using optical emission spectroscopy techniques. The rotational, vibrational, and excitation temperatures along with the electron density are determined from OH (A2Σ → X2Π) band and the Stark broadening of the hydrogen atomic line at 486.1 nm, respectively. The temporal evolution and spatial distribution of charged and reactive species in this plasma are also numerically studied by a Global scheme and a two-dimension fluid model based on drift–diffusion approximation. A kinetic dominated by electron collisions is obtained for this plasma. The generation and movement of electrons, positive and negative ions in the wire-to-multiwire configuration are analyzed and discussed according to changes the electric field and plasma frequency. It is shown that the density of both charged and reactive species increases by adding a small amount of argon to the oxygen plasma while the electron temperature reduces in this configuration. A high level of agreement is observed between the experimental and simulation results for the electron density and temperature in this DBD plasma.

An experimental and kinetic study of OH(A2Σ+) formation and quenching in ammonia-hydrogen-air flames

This work provides a kinetic and experimental investigation of excited radical OH(2Σ+) (also referred to as OH*) in NH3H2-air flames. A counterflow burner is used to stabilize laminar diffusion flames over wide ranges of ammonia fraction in the fuel blend (0.2 ≤ xNH3 ≤ 0.8) and strain rate (40 ≤ a ≤ 200/s). Using an intensified camera or a spectrometer coupled to a Cassegrain optical system, spatially resolved and spatially integrated OH(A2Σ+-X2Π) chemiluminescence intensities are measured. These data are used to challenge a kinetic mechanism largely developed from existing literature schemes. Measurements and simulations show that two distinct OH* peaks exist in spatially resolved profiles for intermediate ammonia fractions in the fuel blend. Sensitivity analyses identified that reactions N2O+H=N2+OH* and H+O+M=OH*+M, respectively pertinent to NH3 and H2 oxidation routes, are responsible for the formation of OH*. The proposed kinetic mechanism gives a remarkable portrait of the empirical data recorded in diffusion flames as well as in premixed NH3H2-air flames from the literature. Nevertheless, the contribution of reaction N2O+H=N2+OH* in the formation of OH* in the peak closest to the fuel side of diffusion flames is consistently overpredicted. Consequently, the frequency factor of the N2O+HN2+OH* reaction is adjusted to A = 1.35 × 1014 cm3mol−1s−1, which significantly improves predictions of spatially integrated and spatially resolved OH* intensities for all the diffusion and premixed flames examined.

A low power microwave room-temperature air plasma jet at atmospheric pressure

An atmospheric pressure low power microwave-induced air plasma source at 2.45 GHz is presented in this Letter. The device was capable of self-igniting air and generating plasma with only 50 W microwave input power and without any extra trigger. Its sustaining power was as low as 10 W, and the gas temperature of plasma tail flame measured by a fiber optic thermometer was about 32 °C. Spectroscopic measurements showed strong OH(A2Σ+→X2Π) bands at 306–310 nm and oxygen atomic lines OI (3p5P → 3s5S) at 777.1 nm and OI (3p3P → 3s3S) at 844.6 nm. NO−γ(A2Σ+→X2Πr) from 200 to 300 nm was also detected in this air plasma jet. This portable plasma apparatus offers potential for air plasma applications in the biomedical fields.

Nonadiabatic Reactive Quenching of OH(A2Σ+) by H2: Origin of High Vibrational Excitation in the H2O Product.

The nonadiabatic dynamics of the reactive quenching channel of the OH(A2Σ+) + H2/D2 collisions is investigated with a semiclassical surface hopping method, using a recently developed four-state diabatic potential energy matrix (DPEM). In agreement with experimental observations, the H2O/HOD products are found to have significant vibrational excitation. Using a Gaussian binning method, the H2O vibrational state distribution is determined. The preferential energy disposal into the product vibrational modes is rationalized by an extended Sudden Vector Projection model, in which the h and g vectors associated with the conical intersection are found to have large projections with the product normal modes. However, our calculations did not find significant insertion trajectories, suggesting the need for further improvement of the DPEM.

Generation of High-Density Pulsed Gas–Liquid Discharge Plasma Using Floating Electrode Configuration at Atmospheric Pressure

In this paper, a high-density gas–liquid discharge plasma is obtained combined with nanosecond pulse voltage and a floating electrode. The discharge images, the waveforms of pulse voltage and discharge current, and the optical emission spectra are recorded. Gas temperature and electron density are calculated by the optical emission spectra of N2 (C3Πu → B3Πg) and the Stark broadening of Hα, respectively. The emission intensities of N2 (C3Πu → B3Πg), N2+ (B2Σ → X2Π), OH (A2Σ → X2Π), O (3p5P → 3s5S0), He (3d3D → 3p3P20), gas temperature, and electron density are acquired by optical emission spectra to discuss plasma characteristics varying with spatial distribution, discharge gap, and gas flow rate. The spatial distributions of discharge characteristics, including gas temperature, electron density, and emission intensities of N2 (C3Πu → B3Πg), N2+ (B2Σ → X2Π), OH (A2Σ → X2Π), O (3p5P → 3s5S0), and He (3d3D → 3p3P20), are presented. It is found that a high-density discharge plasma with the electron density of 2.2 × 1015 cm−3 and low gas temperature close to room temperature is generated. While setting the discharge gap distance at 10 mm, the discharge area over liquid surface has the largest diameter of 20 mm; under the same conditions, electron density is in the order of 1015 cm−3, and gas temperature is approximately 330 K. In addition, the discharge plasma characteristics are not kept consistent in the axial direction, in which the emission intensities of N2+ (B2Σ → X2Π), N2 (C3Πu → B3Πg), OH (A2Σ → X2Π), and gas temperature increased near the liquid surface. As the discharge gap is enlarged, the gas temperature increases, whereas the electron density remains almost constant. Moreover, as the gas flow rate was turned up, the electron density increased and the gas temperature was kept constant at 320 K.

First Observations of Mesospheric OH Emission Profiles from OMPS/LP

Abstract The hydroxyl radical (OH) is one of the most reactive trace species and plays several important roles in the photochemical equilibrium and energy balance in the mesosphere. Global observations of OH from satellite instruments have a role to play in the study of OH and water vapor variations. This study describes an advanced algorithm to detect mesospheric OH emission profiles from the Suomi NPP satellite Ozone Mapping and Profiler Suite Limb Profiler (OMPS/LP). A triplet technique has been adapted to the OMPS/LP radiance measurements for determining OH emission signatures and OH index (OHI) from the OH A2Σ+-X2Π 0-0 band near the 308.8-nm wavelength. The derived mesospheric profiles provide an overall picture of the vertical distribution of OHI between 55 and 84 km and seasonal and latitudinal variability of the strength and height of the OHI. The observed annual cycle is correlated with the water vapor cycle and anticorrelated with the mesospheric temperature cycle. The data show that the relationships persist during the period of April 2012–December 2020. The seasonal behavior of OHI may be associated with variations in solar illumination or mesospheric water vapor abundance. The influence of solar illumination is dominant in the midlatitudes, while the OHI pattern is dominated by water vapor photolysis and other influences in the tropics.

Promoting streamer propagation, active species generation and trichloroethylene degradation using a three-electrode nanosecond pulsed sliding DBD nanosecond plasma

This work is devoted to exploring the streamer dynamic of a nanosecond pulsed sliding dielectric barrier discharge (SLDBD) based on a three-electrode geometry, and evaluating its effectiveness for the degradation of a representative chlorinated volatile organic compound (VOC)-trichloroethylene (TCE) at ambient temperature. The surface streamer of nanosecond pulsed SLDBD presents two distinct phases: primary streamer with higher velocity and secondary streamer with lower velocity. The luminous intensity, propagation distance, and propagation velocity of the primary streamer are greatly promoted by increasing the negative DC voltage (U-DC) applied at the third electrode, whereas only a little difference can be observed in the luminous intensity and propagation velocity for the secondary streamer with different U-DC. The surface potential difference between the pulsed excited high-voltage and the negatively biased third electrodes (Upulse-DC) is the major cause for streamers propagation because of the increased electric field at the streamer head. The production of excited species such as N2(C3Πu), N2+(B2Σu+), and OH(A2Σ) are promoted with increasing U-DC. The formation of N2(C3∏u→B3∏g,337 nm ) accompanies the streamer propagation process by electrons impact process. The TCE degradation experiment exhibits that the degradation efficiency and energy yield are significantly improved when Upulse-DC exceeds 20 kV where an SLDBD plasma is ignited, which can be attributed to the promoted surface streamers propagation as well as greater number of chemical active species.

Spatial characteristics of nanosecond pulsed micro-discharges in atmospheric pressure He/H2O mixture by optical emission spectroscopy

Atmospheric pressure micro-discharges in helium gas with a mixture of 0.5% water vapor between two pin electrodes are generated with nanosecond overvoltage pulses. The temporal and spatial characteristics of the discharges are investigated by means of time-resolved imaging and optical emission spectroscopy with respect to the discharge morphology, gas temperature, electron density, and excited species. The evolution of micro-discharges is captured by intensified CCD camera and electrical properties. The gas temperature is diagnosed by a two-temperature fit to the ro-vibrational OH(A2Σ+–X2Π, 0–0) emission band and is found to remain low at 425 K during the discharge pulses. The profile of electron density performed by the Stark broadening of H α 656.1-nm and He I 667.8-nm lines is uniform across the discharge gap at the initial of discharge and reaches as high as 1023 m−3. The excited species of He, OH, and H show different spatio-temporal behaviors from each other by the measurement of their emission intensities, which are discussed qualitatively in regard of their plasma kinetics.

Quantum Dynamics of Nonadiabatic Renner-Teller Effects in Atom + Diatom Collisions.

We review the quantum nonadiabatic dynamics of atom + diatom collisions due to the Renner-Teller (RT) effect, i.e., to the Hamiltonian operators that contain the total spinless electronic angular momentum L̂. As is well-known, this rovibronic effect is large near collinear geometries when at least one of the interacting states is doubly degenerate. In general, this occurs in insertion reactions and at short-range, where the potential wells exhibit deep minima and support metastable complexes. Initial-state-resolved reaction probabilities, integral cross sections, and thermal rate constants are calculated via the real wavepacket method, solving the equation of motion with an approximated or with an exact spinless RT Hamiltonian. We present the dynamics of 10 single-channel or multichannel reactions showing how RT effects depend on the product channels and comparing with the Born-Oppenheimer (BO) approximation or coexisting conical-intersection (CI) interactions. RT effects not only can significantly modify the adiabatic dynamics or correct purely CI results, but also they can be very important in opening collision channels which are closed at the BO or CI level, as in electronic-quenching reactions. In the OH(A2Σ+) + Kr electronic quenching, where both nonadiabatic effects (CI and RT) coexist, they are in competition because CI dominates the reactivity but RT couplings reduce the large CI cross section and open a CI-forbidden evolution toward products, so that CI + RT quantum results are in good agreement with experimental or semiclassical findings. The different roles of these couplings are due to the unlike nuclear geometries where they are large: rather far from or near to linearity for CI or RT, respectively. The OH(A2Σ+) + Kr electronic quenching was investigated with the exact RT Hamiltonian, validating the approximated one, which was employed for all other collisions.

Characteristics of a kHz helium atmospheric pressure plasma jet interacting with two kinds of targets

This study investigates the influence of two types of target, skin tissue and cell culture medium, with different permittivities on a kHz helium atmospheric pressure plasma jet (APPJ) during its application for wound healing. The basic optical–electrical characteristics, the initiation and propagation and the emission spectra of the He APPJ under different working conditions are explored. The experimental results show that, compared with a jet freely expanding in air, the diameter and intensity of the plasma plume outside the nozzle increase when it interacts with the pigskin and cell culture medium targets, and the mean velocity of the plasma bullet from the tube nozzle to a distance of 15 mm is also significantly increased. There are also multiple increases in the relative intensity of OH (A2Σ → X2Π) and O (3p5S–3s5S) at a position 15 mm away from nozzle when the He APPJ interacts with cell culture medium compared with the air and pigskin targets. Taking the surface charging of the low permittivity material capacitance and the strengthened electric field intensity into account, they make the various characteristics of He APPJ interacting with two different targets together.

Temporal Variations of Optical Emission Spectra in Microwave-Excited Plasma in Saturated Water Vapor under Reduced Pressure during Photoresist Removal

Mechanisms of photoresist removal were investigated using microwave-excited plasma in saturated water vapor under a reduced pressure condition (approx. 6 kPa). A few seconds of white emission were observed at the beginning of photoresist removal. To ascertain the species of spectra, optical emission spectroscopy was used for photoresist removal from a Si wafer. Emission spectra of OH (A2Σ – X2Π), Hα (656 nm), and O (777 nm) derived from dissociation of water molecules were observed. Other emission spectra attributed to CO molecules were also detected and identified as the Ångström system (B1Σ – A1Π). This result indicates CO molecule generation during photoresist removal. The CO molecule emission intensity reached a maximum value at 1.1 s after plasma ignition, whereas those of OH, Hα, and O reached a minimum value at almost identical time. Furthermore, normalized emission spectra shape from CO molecules during photoresist removal were almost identical for Δv = +1, 0, -1, -2, -3, and -4. Rotational and vibrational temperatures of the CO molecules during photoresist removal were found to be almost constant and to be 1500 and 2500 K, respectively. These results suggest increased CO molecular density above the Si wafer at 1.1 s.

Photodissociation Dynamics of H2O via the Ẽ' (1B2) Electronic State.

Photodissociation dynamics of H2O via the Ẽ'1B2 state were studied using the high-resolution H atom photofragment translational spectroscopy method, in combination with the tunable vacuum ultraviolet free electron laser (VUV FEL). The measured translational energy spectra allow us to determine the respective quantum state population distributions for the nascent OH(X2Π) and OH(A2Σ+) photofragments. Analyses of the quantum state population distributions show both the ground and electronically excited OH fragments to be formed with moderate vibrational excitation but with highly rotational excitation. Unlike the dissociation via the lower-lying electronic states, where OH(X) is the major fragment, the OH(A) products are predominant via the Ẽ' state. These products are mainly ascribed to a fast dissociation on the B̃1A1 state surface after nonadiabatic transitions from the initial excited Ẽ' state to the B̃ state. Meanwhile, another dissociation pathway from the Ẽ' state to the 1B2 3pb2 state, followed by coupling to the 1A2 3pb2 state, is also observed, which yields the OH(X) + H and O(3P) + 2H products.

On the rotational–translational equilibrium in non-thermal argon plasmas at atmospheric pressure

This work examines the rotational–translational equilibrium in non-thermal, argon-based plasmas at atmospheric pressure. In particular, rotational temperatures (T rot) and neutral gas temperatures (T g) are compared along the axis of plasma columns sustained by either radiofrequency (RF) or microwave (MW) electromagnetic fields. Water vapours or N2 admixtures are added to the high-purity argon plasmas to record the rotational temperatures from the emission spectra of either the OH(A2Σ + − X2Π i ) or the N2 +(B2Σ u + − X2Σ g + ) rovibrational systems. T g values are also deduced from the line broadening of selected Ar emission lines using an hyperfine spectrometer. In the MW Ar/H2O plasma, T g decreases from ∼2100 K close to the wave launcher to ∼1600 K near the end of the plasma column, while T rot is mostly constant in the 1500 K range. In presence of N2 admixtures instead of water vapours, T g is higher by about 300 K (from ∼2400 K to ∼1900 K), while T rot decreases from ∼3200 K to ∼2750 K along the plasma column. A discrepancy between T g and T rot is also observed in the much colder RF plasmas with T g ∼ 400 K and T rot ∼ 515 K. Such departure from the rotational–translational equilibrium in both plasmas is ascribed to the influence of electrons competing with neutrals to impose their own temperature on the distribution of rotational levels of both ground and excited states.

Temporal resolved atomic emission spectroscopy on a pulsed electrolyte cathode discharge for improving the detection sensitivity of Cu

Atmospheric pressure electrolyte cathode discharge plasma presents a great potential on detecting heavy metal pollutants. In this paper, a novel microsecond pulsed electrolyte cathode discharge was generated and coupled with temporal resolved atomic emission spectra to analyze Cu element, as one of the representative heavy metals. The waveforms of voltage and current, as well as optical emission spectra of discharge were investigated, and the experimental conditions were optimized. The spatiotemporal resolved spectra of Cu I (324.8 nm), OH (A2Σ–X2Π) and N2 (C3Πu–B3Πg) were diagnosed. The spatiotemporal distributions of gas temperature and electron density were calculated by the rotational temperature of OH (A) and the Stark broadening of Hβ (486.1 nm), respectively. It was found that the optimal detection sensitivity of Cu are obtained under the conditions of HNO3 solution with 1.0 pH value, 3.0 mL/min solution flow rate, 8.5 kV pulse peak voltage, and 100 μs pulse width. The interferences of spectral line of Cu I (324.8 nm) are mainly sourced by the spectral bands of N2 (C-B) and OH (A-X), which could be reduced by the temporal resolved spectra. The limit of detection of Cu was improved from 0.217 mg/L to 0.092 mg/L by acquiring spectra only in 25–100 μs, under the optimal conditions. Furthermore, the gas temperature and electron density play important roles in the spatiotemporal evolution of discharge and the improvement of detection sensitivity for elemental analysis.

State-to-state predissociation dynamics of hydroxyl radical via the A2Σ+ state

ABSTRACT Photo-predissociation dynamics of jet-cooled hydroxyl radical (OH) via several rovibrational levels (v′ = 2–4, N′ = 0–2, J′ = 0.5–2.5, F 1) in the A2Σ+ state are studied using the high–n Rydberg-atom time-of-flight (HRTOF) technique. Spin–orbit branching fractions and angular distributions of the H(2S) + O(3PJ = 2,1,0) product channels are measured in the product translational energy distributions. The A2Σ+ v′ = 2 and 3 states of OH predissociate predominantly via the single 14Σ− repulsive state, while the A2Σ+ v′ = 4 state predissociates via the 14Σ−, 12Σ−, and 14Π repulsive states and quantum interferences among these dissociation pathways play an important role in the O(3PJ = 2,1,0) product fine-structure state distribution. The experimental O(3PJ) product spin–orbit branching ratios are in excellent agreement with the full quantum multichannel scattering calculations that include all the interactions in the crossing region, recoupling zone, and asymptotic zone [Parlant and Yarkony, J. Chem. Phys. 110, 363 (1999)]. The product angular distributions strongly depend on the rotational transitions and rotational levels in the A2Σ+ state. The measured anisotropy parameters are in reasonable agreement with predictions from the simulation programme (Betaofnu) [Kim et al., J. Chem. Phys. 125, 133316 (2006)], using dissociation lifetime, excitation frequency, rotational level, and rotational constant. The predissociation time scales of OH A2Σ+ are determined to be 130 ± 30 ns and ≥ 14 ± 3 ps for the v′ = 2, N′ = 2, J′ = 2.5 and v′ = 4, N′ = 0, J′ = 0.5 levels, respectively.

Plasma characteristics and mode transition of atmospheric pressure gas–liquid discharge oxygen plasma

In this paper, a capacitor assisted AC high-voltage was employed to generate a gas–liquid discharge in pure oxygen at atmospheric pressure. The discharge images, waveforms of voltage and discharge current, and optical emission spectra of plasma were diagnosed for the purpose of investigating the discharge modes. The gas temperature (Tg), excitation temperature of hydrogen (Texc), and electron density (ne) were calculated by the spectra of OH (A2Σ–X2Π), the intensity ratio of Hα and Hβ, and the Stark broadening of Hβ, respectively. The effects of applied voltage and capacitance value on the mode transition of discharge were also discussed. It is found that due to the presence of capacitor, not only is the unlimited growth of discharge current restrained, but the transition of discharge mode is also controllable. There are three discharge modes of gas–liquid discharge oxygen plasma (GLDOP), and with the increase of applied voltage or capacitance value, discharge modes are transited from the streamer mode, to the glow-like mode, and to the abnormal glow/arc mode. With the mode transition, the Tg and Texc of GLDOP increase and the ne decreases. In contrast, the change of Tg and ne is negligible when GLDOP maintains one kind of discharge mode.

Non-adiabatic quantum dynamics of the electronic quenching OH(A2Σ+) + Kr.

We present the dynamics of the electronic quenching OH(A2Σ+) + Kr(1S) → OH(X2Π) + Kr(1S), with OH(A2Σ+) in the ground ro-vibrational state. This study relies on a new non-adiabatic quantum theory that uses three diabatic electronic states Σ+, Π', and Π'', coupled by one conical-intersection and nine Renner-Teller matrix elements, all of which are explicitly considered in the equation of the motion. The time-dependent mechanism and initial-state-resolved quenching probabilities, integral cross sections, thermal rate constants, and thermally-averaged cross sections are calculated via the real wavepacket method. The results point out a competition among three non-adiabatic pathways: Σ+ ↔ Π', Σ+ ↔ Π'', and Π' ↔ Π''. In particular, the conical-intersection effects Σ+-Π' are more important than the Renner-Teller couplings Σ+-Π', Σ+-Π'', and Π'-Π''. Therefore, Π' is the preferred product channel. The quenching occurs via an indirect insertion mechanism, opening many collision complexes, and the probabilities thus present many oscillations. Some resonances are still observable in the cross sections, which are in good agreement with previous experimental and quasi-classical findings. We also discuss the validity of more approximate quantum methods.

On the nonadiabatic collisional quenching of OH(A) by H2: a four coupled quasi-diabatic state description.

A four-state diabatic potential energy matrix (DPEM), Hd, for the description of the nonadiabatic quenching of OH(A2Σ+) by collisions with H2 is reported. The DPEM is constructed as a fit to adiabatic energies, energy gradients, and derivative couplings obtained exclusively from multireference configuration interaction wave functions. A four-adiabatic-electronic-state representation is used in order to describe all energetically accessible regions of the nuclear coordinate space. Partial permutation-inversion symmetry is incorporated into the representation. The fit is based on electronic structure data at 42 882 points, described by over 1.6 million least squares equations with a root mean square (mean unsigned) error of 178(83) cm-1. Comparison of ab initio and Hd determined minima, saddle points, and energy minimized points on C2v, Cs, C∞v, and C1 (noncoplanar) portions of two conical intersection seams are used to establish the accuracy of the Hd.

Quantitative 2-D OH thermometry using spectrally resolved planar laser-induced fluorescence.

A novel method is presented for quantitative two-dimensional temperature measurement in combustion gases. This method, namely spectrally resolved planar laser-induced fluorescence thermometry, utilizes a high-power, wavelength-tunable and narrow-linewidth CW laser to access the spectral lineshapes of a key combustion intermediate, the hydroxyl radical (OH), and enables high-fidelity and calibration-free quantification of non-uniform temperature fields in complex reacting flows. Specifically, the R1(11)/R1(7) line pair of the OH A2Σ+-X2Π(0,0) rovibronic band was probed with laser radiation near 306.5nm, and their fluorescence ratios were used to infer temperature. Preliminary demonstrations of this thermometry method were performed in a series of burner-stabilized CH4-air flames.