The Quantum Yield of NO(sub 2) from Photodissociation of Peroxynitric Acid (HO(sub 2)NO(sub 2))
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upper atmospher stratospheric ozone nitrogen oxide↗
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PotLib 2023: New version of a potential energy surface library for chemical systems
POTLIB is a library of global and semiglobal potential energy surface subprograms. The library currently features 410 entries, including both single-state entries and multi-state entries. When one calls the routine of a single-state entry, it returns the ground-electronic-state adiabatic potential energy surface at the input geometry. In addition, some entries also return the gradient of the surface. Further, when one calls a multi-state entry, it returns a diabatic potential energy matrix (DPEM). If the entry also has the gradient of the DPEM, one can compute adiabatic surfaces, their gradients, and the nonadiabatic coupling vectors (NACs) from the DPEM and its gradient by diagonalization. Some but not all the routines conform to one of a set of standard interfaces. The goal is to facilitate chemical dynamics research by collecting and disseminating a comprehensive collection of state-of-the-art potential energy routines (developed by a wide, international group of researchers) with systematic and well-defined interfaces for use with chemical dynamics programs. Systems in the library include CHArO 2 , CHN 2 O + , CH 2 O, CH 2 O 2 , CH 3 N 2 , CH 3 O, CH 4 , CH 4 Br, CH 4 Cl, CH 4 F, CH 4 O, CH 4 OCl, CH 4 OF, CH 4 OH, CH 5 , CH$^{+}_{5}$, CH 5 N, CH 5 O 2 , CH 8 O 2 , C 2 H 2 N 2 O, C 2 H 2 O, C 2 H 4 N, C 2 H 4 O 4 , C 2 H 6 Cl, C 2 H 6 F, C 2 H 6 H, C 2 H 6 O, C 2 H 6 OH, C 2 H 7 , C 2 O 2 , C 3 H 4 O 2 , C 3 H 7 NO, C 6 H 6 O, C 6 H 6 S, C 7 H8S, HBrCl, HCl 2 , HF 2 , HI 2 , HLiF, HNaF, HO 2 , HO 3 , HOBr, HSiO, H 2 Br, H 2 ClO, H 2 F, H 2 F 2 , H 2 FO, H 2 Na, H 2 O, H 2 O 2 , H 2 OBr, H 3 , H 3 Cl, H 3 ClN, H 3 ClO, H 3 N, H 3 O, H 3 O 2 , H$^{+}_{3}$, H 3 S, H 4 ClSi, H 4 N, H 4 NO, H 4 O 2 , H 5 GeO, H 5 Si, H$^{+}_{7}$, Al m H n , Al n , Ar N O, K 2 Rb 2 , NO 2 , N 2 O, N 2 O 2 , N 3 , N 4 , O 3 , and O 4 .
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Oxidation of methylamine
A detailed chemical kinetic model for oxidation of methylamine has been developed, based on theoretical work and a critical evaluation of data from the literature. In this work, the rate coefficients for the reactions of CH 3 NH 2 + O 2 → CH 2 NH 2 / CH 3 NH + HO 2 , CH 3 NH 2 + H → CH 3 + NH 3 , CH 3 NH → CH 2 NH 2 , and CH 3 NH + O 2 → CH 2 NH + HO 2 were calculated from ab initio theory. The mechanism was validated against experimental results from batch reactors, flow reactors, shock tubes, and premixed flames. The model predicts satisfactorily explosion limits for CH 3 NH 2 and its oxidation in a flow reactor. However, oxidation in the presence of nitric oxide, which strongly promotes reaction at lower temperatures, is only described qualitatively. Furthermore, calculated flame speeds are higher than reported experimental values; the model does not capture the inhibiting effect of the NH 2 group in CH 3 NH 2 compared to CH 4 . More work is desirable to confirm the products of the CH 3 NH + NO reaction and to look into possible pathways to NH 3 in methylamine oxidation.
10 SYNTHETIC FUELS↗
Measurements of the rate constant of HOsub2 + NOsub2 + Nsub2 --> HOsub2NOsub2 + Nsub2 using near-infrared wavelength-modulation spectroscopy and UV-visible absorption spectroscopy
Rate coefficients for the reaction HO(sub 2)+ NO(sub 2) + N(sub 2) --> HO(sub 2)NO(sub 2) + N(sub 2) (reaction 1) were measured using simultaneous near-IR and UV spectroscopy from 220 to 298 K and from 45 to 200 Torr.
UV spectroscopy wavelength modulation spectroscopy↗
Theoretical and kinetic modeling study of hydrazine oxidation
The present work constitutes the first theoretical and kinetic modeling study of hydrazine oxidation, which may be important for burnout in ammonia-fueled combustion. The kinetics of the oxidation of N 2 H 4 , N 2 H 3 and tHNNH by molecular oxygen were investigated via a quantum chemistry/canonical transition state theory approach. Geometries and anharmonic frequencies were obtained with density functional theory, and energies from coupled cluster calculations (CCSD(T)) extrapolated to the infinite basis set limit, with corrections for core-valence electron correlation, scalar relativistic effects, and higher level correlation up to lambda coupled cluster, CCSDT(Q) Λ . The key reactions occurred on the N 2 H 4 O 2 potential energy surface, where the results indicated a fast reaction of N 2 H 3 with HO 2 via singlet adducts to yield tHNNH + H 2 O 2 and HNN(H)O + H 2 O, while reaction on the triplet surface proceeds via a bound complex followed by a tight, submerged barrier to yield N 2 H 4 + O 2 . The results were incorporated in a detailed reaction mechanism, which was used to interpret the shock tube results from Michel and Wagner (1965) on the effect of O 2 on hydrazine conversion at 1100–1400 K. The kinetic model captured qualitatively the observed behavior, but underestimated the reaction rate under oxidizing conditions. The hydrazine pyrolysis chemistry dominated conversion at reducing conditions and/or high temperature. At oxidizing conditions and intermediate temperatures (≲ 1400 K), reactions of N 2 -amines with HO 2 and O 2 were important for the oxidation rate.
Ab initio calculations↗
Kinetic studies of excited singlet oxygen atom O( 1 D) reactions with ethanol
In this work, themultichannel reaction of excited singlet oxygen atom with ethanol, O( 1 D) + C 2 H 5 OH (1), was studied in a photolysis flow reactor coupled with mid-infrared Faraday rotation spectroscopy (FRS) and UV-IR direct absorption spectroscopy (DAS) at 297 K with reactor pressures of 60, 120, and 150 Torr (bath He). The excited singlet oxygen atom was generated through the photolysis of O 3 at 266 nm. The photon flux and O( 1 D) concentrations were determined by in situ actinometry based on O 3 depletion. Temporal profiles of OH and H 2 O were monitored via DAS signals at ca. 3568.62 and 3568.29 cm –1 , while temporal profiles of HO 2 were measured via FRS signals at ca. 1396.90 cm –1 . The branching ratios of the target reaction (1) were determined by fitting temporal profiles to simulations from an in-house reaction mechanism. Two major reaction channels were identified as CH 3 CHOH + OH and CH 3 O + CH 2 OH, and their branching ratios were determined as 0.46 ± 0.12 and 0.42 ± 0.11, respectively. A specific HO 2 + RO 2 reaction between HO 2 and O 2 CH 2 CH 2 OH (β-RO 2 ) at the low-temperature range is estimated in this work as HO 2 + O 2 CH 2 CH 2 OH → products with a rate constant of 7 × 10 –12 cm 3 molecule –1 s –1 .
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Experimental and modeling study of the autoignition behavior of a saturated heterocycle: Pyrrolidine
Experiments are conducted in both rapid compression machine (RCM) and shock tube (ST) to better quantify autoignition behavior (e.g., ignition delay, heat release) and understand heteroatomic effects in heterocyclic compounds, which are important reference components for the combustion of biomass-derived liquid fuels. These tests focus on the nitrogen-containing, five-membered saturated ring, pyrrolidine, at diluted conditions covering pressures of 20 and 50 bar, temperatures of 720–1450 K and a range of stoichiometries (ϕ = 0.5–2). A chemical kinetic model is developed and coupled to an existing combustion kinetics framework describing key nitrogen containing intermediates (e.g. pyrrole, ammonia and NOx). H-abstraction reactions by OH, H, CH 3 and HO 2 , are determined using ab-initio transition state theory methods, while analogies to cyclopentane are adopted for many other reactions, such as ring-opening. Here, the autoignition measurements reveal the lack of negative temperature coefficient (NTC) behavior and low-temperature chemistry for pyrrolidine, as opposed to its saturated hydrocarbon analogue, cyclopentane. Interestingly, at the lowest temperatures (T < 750 K), the reactivity of cyclopentane is greater than pyrrolidine, while at higher temperatures, pyrrolidine becomes more reactive. Agreement between the experimental measurements and the model is good, and it is found that H-abstraction reactions by HO 2 and ensuing chemistry play key roles in controlling the reactivity of this cyclic amine. Most of the fluxes, i.e., >70 %, are predicted to move through 1- or 2-pyrroline (C 4 H 7 N) and then the cyclic C 4 H 6 N radical, at both lower and higher temperatures, to form either CH 2 CHCHCHNH via ring-opening or pyrrole via β-scission. It appears that the ring opens more easily at lower temperature whereas the C–H β-scission dominates at higher temperature and lower pressure, such that the reaction of the fuel radical intermediate carrying an unpaired electron on the nitrogen atom with HO 2 is the next most notable in promoting oxidation. When comparing pyrrolidine and cyclopentane, which exhibits distinct pathways in different temperature regimes, the pyrrolidine pathways and sensitivity analysis align more closely to the high temperature case of cyclopentane where the important role of HO 2 radicals is seen to provide chain branching through HO 2 reaction with the fuel, accompanied by H 2 O 2 formation and decomposition to OH. The formation of 5-membered diene rings and ring opening reactions are also found to be highly relevant. Of particular note, it is found that there is little influence of small molecule nitrogen-chemistry, e.g., NH 2 , HCN, NO/NO 2 on the reactivity of the pyrrolidine mixtures investigated here where no recirculated combustion gases are included.
Autoignition↗
Kinetics and Mechanism of the Singlet Oxygen Atom Reaction with Dimethyl Ether
Here, we combine in situ laser spectroscopy, quantum chemistry, and kinetic calculations to study the reaction of a singlet oxygen atom with dimethyl ether. Infrared laser absorption spectroscopy and Faraday rotation spectroscopy are used for the detection and quantification of the reaction products OH, H 2 O, HO 2 , and CH 2 O on submillisecond time scales. Fitting temporal profiles of products with simulations using an in-house reaction mechanism allows product branching to be quantified at 30, 60, and 150 Torr. The experimentally determined product branching agrees well with master equation calculations based on electronic structure data and transition state theory. The calculations demonstrate that the dimethyl peroxide (CH 3 OOCH 3 ) generated via O-insertion into the C–O bond undergoes subsequent dissociation to CH 3 O + CH 3 O through energetically favored reactions without an intrinsic barrier. This O-insertion mechanism can be important for understanding the fate of biofuels leaking into the atmosphere and for plasma-based biofuel processing technologies.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Two-dimensional mapping of absolute OH densities in an atmospheric pressure plasma effluent via planar laser-induced fluorescence: effects of He/H 2 O and He/O 2 mixtures in N 2 and air, with and without solid targets
Planar laser-induced fluorescence (LIF) was employed to measure the absolute density of hydroxyl radicals (OH) in the effluent of the COST Reference Microplasma Jet for two feed gas mixtures: He/H 2 O and He/O 2 . Experiments were conducted with the effluent propagating into air and N 2 environments. For the He/H 2 O case, measurements were also performed with the effluent impinging on a solid target at varying distances from the jet nozzle. Calibration of the OH-LIF signal from the COST-Jet was achieved by comparing it to a reference signal generated by the photofragmentation of H 2 O 2 . Results demonstrated that OH densities were sustained longer when the effluent propagates in a nitrogen environment compared to air, particularly with water added to the feed gas. The broader OH distribution in N 2 suggests slower consumption due to the absence of oxygen, which accelerates OH depletion in air via reactions involving O 2 and HO 2 . Even when water was not added to the feed, as in the He/O 2 case, appreciable OH densities were observed, due to gas impurities and reactive species interactions with atmospheric humidity, forming reaction fronts that delineate the gas flow. Two-dimensional fluid dynamics simulations elucidated the influence of atmospheric gas entrainment and solid targets on the OH distribution. Experimental trends were further compared with a zero-dimensional chemistry model to explore OH production and consumption mechanisms in air and nitrogen environments.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Materials Data on Ho(SiPt)2 by Materials Project
HoPt2Si2 crystallizes in the tetragonal P4/nmm space group. The structure is three-dimensional. Ho is bonded in a 12-coordinate geometry to eight Pt and eight Si atoms. There are four shorter (3.20 Å) and four longer (3.26 Å) Ho–Pt bond lengths. There are four shorter (3.19 Å) and four longer (3.21 Å) Ho–Si bond lengths. There are two inequivalent Pt sites. In the first Pt site, Pt is bonded in a 9-coordinate geometry to four equivalent Ho and five Si atoms. There are one shorter (2.38 Å) and four longer (2.43 Å) Pt–Si bond lengths. In the second Pt site, Pt is bonded to four equivalent Ho and four equivalent Si atoms to form distorted PtHo4Si4 tetrahedra that share corners with twelve equivalent SiHo4Pt4 tetrahedra, edges with two equivalent SiHo4Pt4 tetrahedra, edges with four equivalent PtHo4Si4 tetrahedra, and faces with four equivalent PtHo4Si4 tetrahedra. All Pt–Si bond lengths are 2.48 Å. There are two inequivalent Si sites. In the first Si site, Si is bonded in a 9-coordinate geometry to four equivalent Ho and five Pt atoms. In the second Si site, Si is bonded to four equivalent Ho and four equivalent Pt atoms to form distorted SiHo4Pt4 tetrahedra that share corners with twelve equivalent PtHo4Si4 tetrahedra, edges with two equivalent PtHo4Si4 tetrahedra, edges with four equivalent SiHo4Pt4 tetrahedra, and faces with four equivalent SiHo4Pt4 tetrahedra.
36 MATERIALS SCIENCE↗
Materials Data on Ho(SiRh)2 by Materials Project
HoRh2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ho is bonded in a 8-coordinate geometry to eight equivalent Rh and eight equivalent Si atoms. All Ho–Rh bond lengths are 3.22 Å. All Ho–Si bond lengths are 3.12 Å. Rh is bonded to four equivalent Ho and four equivalent Si atoms to form a mixture of distorted face, edge, and corner-sharing RhHo4Si4 tetrahedra. All Rh–Si bond lengths are 2.40 Å. Si is bonded in a 9-coordinate geometry to four equivalent Ho, four equivalent Rh, and one Si atom. The Si–Si bond length is 2.42 Å.
36 MATERIALS SCIENCE↗
Materials Data on Ho(SiPd)2 by Materials Project
HoPd2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ho is bonded in a 8-coordinate geometry to eight equivalent Pd and eight equivalent Si atoms. All Ho–Pd bond lengths are 3.25 Å. All Ho–Si bond lengths are 3.14 Å. Pd is bonded to four equivalent Ho and four equivalent Si atoms to form a mixture of distorted edge, corner, and face-sharing PdHo4Si4 tetrahedra. All Pd–Si bond lengths are 2.47 Å. Si is bonded in a 9-coordinate geometry to four equivalent Ho, four equivalent Pd, and one Si atom. The Si–Si bond length is 2.31 Å.
36 MATERIALS SCIENCE↗
Materials Data on Ho(SiPt)2 by Materials Project
HoPt2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ho is bonded in a 8-coordinate geometry to eight equivalent Pt and eight equivalent Si atoms. All Ho–Pt bond lengths are 3.23 Å. All Ho–Si bond lengths are 3.18 Å. Pt is bonded to four equivalent Ho and four equivalent Si atoms to form a mixture of distorted edge, face, and corner-sharing PtHo4Si4 tetrahedra. All Pt–Si bond lengths are 2.47 Å. Si is bonded in a 9-coordinate geometry to four equivalent Ho, four equivalent Pt, and one Si atom. The Si–Si bond length is 2.32 Å.
36 MATERIALS SCIENCE↗
Studies of Low and Intermediate Temperature Oxidation of Propane up to 100 Atm in a Supercritical-Pressure Jet-Stirred Reactor
Here, the low and intermediate temperature oxidation of propane has been investigated by using a novel supercritical pressure jet stirred reactor (SP-JSR) with and without 20% CO 2 additions at fuel lean and rich conditions at 10 and 100 atm and 500–1000 K. The mole fractions of C 3 H 8 , O 2 , CO, CO 2 , CH 2 O, C 2 H 4 , CH 3 CHO, and C 3 H 6 were quantified by using a micro-gas chromatograph (µ-GC). The experiment showed that different from that of 10 atm, at 100 atm only a weak negative temperature coefficient (NTC) behavior was observed because of the significant shift of the intermediate temperature HO 2 chemistry to lower temperature. In addition, at 100 atm, existing models in literatures could successfully capture the onset temperatures of the low and intermediate chemistry, while under-predict the fuel oxidation quantitatively and fail to capture the NTC behavior between 650 and 780 K at both fuel lean and rich conditions. Similar discrepancy was observed in studies of n-butane and dimethyl ether (DME) oxidations in literatures, implying that there existed large uncertainties in hierarchy model development of fuels with low temperature chemistries at extremely high pressures. Reaction pathways and sensitivity analyses showed that RO 2 competing reactions through (P1) RO 2 = QOOH, (P2) RO 2 = C 3 H 6 + HO 2 , (P3) RO 2 + CH 2 O/HO 2 = RO 2 H + HCO / O 2 dominated the low and intermediate temperature chemistries, followed by HO 2 / H 2 O 2 chemistry at 100 atm, which differed from the dominant pathway through QOOH consumption reactions at lower pressures. Especially, P3 is a new pathway of RO 2 consumption at high pressures, which was not observed in importance at low pressures. Special attention should be paid to the accurate computations of n-C 3 H 7 O 2 / i-C 3 H 7 O 2 + CH 2 O and n-C 3 H 7 O 2 / i-C 3 H 7 O 2 + in the P3 pathway and n-C 3 H 7 O 2 / i-C 3 H 7 O 2 decomposition reactions in the P2 pathway at high pressures.
33 ADVANCED PROPULSION SYSTEMS↗
Chemical kinetic interactions of NO with a multi-component gasoline surrogate: Experiments and modeling
Here this work reports an experimental and modeling study on the chemical kinetic interactions of NO with a multi-component gasoline surrogate, namely PACE-20, using a twin-piston rapid compression machine at a stochiometric fuel loading with 20% EGR (exhaust gas recirculation) by mass, pressures of 20 and 40 bar, and temperatures from 700 to 930 K. Five NO concentrations are investigated, namely 0, 20, 50, 70 and 150 ppm, where NO addition effects are characterized through changes in PACE-20 ignition reactivity and heat release characteristics. Experiments indicate that within the low-temperature regime, NO promotes low-temperature heat release rate and main ignition reactivity at low addition levels, with saturation or even inhibiting effects observed at >50 ppm NO addition, while within the NTC/intermediate-temperature regime, adding NO only promotes reactivity. A recently updated, detailed chemical kinetic model with chemistry specific to NOx/hydrocarbons interaction incorporated is used to simulate the experiments, and reasonable agreement is obtained. In-depth sensitivity and rate of production analyses are further performed. The results indicate that NO interacts with PACE-20 via two types of interaction: (a) direct interactions between NO and PACE-20 derivatives, primarily through NO+HO 2 ↔NO 2 +OH and RO 2 +NO↔RO+NO 2 , and (b) indirect interactions between PACE-20 derivatives and NO 2 produced from the direct interactions, primarily through R+NO 2 ↔RO+NO. The observed NO inhibiting effect at low temperatures and 150 ppm NO addition is attributed to the lack of HO 2 radicals to sustain NO consumption via NO+HO 2 ↔NO 2 +OH, and the take-up of inhibiting pathways via RO 2 +NO↔RO+NO 2 . The results also indicate that even with the presence of multiple fuel components, NOx/hydrocarbons interactions are highly selective, and are mainly initiated by the interactions between NO and RO 2 radicals from cyclopentane and ethanol, as well as between NO 2 and R radicals from toluene, 1,2,4-trimethylbenzene and 1-hexene. Further studies on these interactive reactions are therefore highly recommended.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Materials Data on Ho(Al5Fe)2 by Materials Project
HoFe2Al10 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. Ho is bonded in a 10-coordinate geometry to four equivalent Fe and sixteen Al atoms. All Ho–Fe bond lengths are 3.41 Å. There are a spread of Ho–Al bond distances ranging from 3.11–3.64 Å. Fe is bonded in a 10-coordinate geometry to two equivalent Ho and ten Al atoms. There are a spread of Fe–Al bond distances ranging from 2.51–2.71 Å. There are five inequivalent Al sites. In the first Al site, Al is bonded in a 2-coordinate geometry to one Ho, two equivalent Fe, and eight Al atoms. There are a spread of Al–Al bond distances ranging from 2.55–2.99 Å. In the second Al site, Al is bonded in a 2-coordinate geometry to two equivalent Ho, two equivalent Fe, and eight Al atoms. There are a spread of Al–Al bond distances ranging from 2.69–2.81 Å. In the third Al site, Al is bonded in a 12-coordinate geometry to two equivalent Ho, two equivalent Fe, and eight Al atoms. There are a spread of Al–Al bond distances ranging from 2.75–2.90 Å. In the fourth Al site, Al is bonded in a 2-coordinate geometry to two equivalent Ho, two equivalent Fe, and eight Al atoms. There are one shorter (2.59 Å) and one longer (2.80 Å) Al–Al bond lengths. In the fifth Al site, Al is bonded to one Ho, two equivalent Fe, and nine Al atoms to form a mixture of distorted corner and face-sharing AlHoAl9Fe2 cuboctahedra. The Al–Al bond length is 2.70 Å.
36 MATERIALS SCIENCE↗
Materials Data on Ho(BC)2 by Materials Project
HoB2C2 crystallizes in the tetragonal P4_2/mmc space group. The structure is three-dimensional. Ho is bonded in a 8-coordinate geometry to eight equivalent B and eight equivalent C atoms. All Ho–B bond lengths are 2.73 Å. All Ho–C bond lengths are 2.70 Å. B is bonded in a 2-coordinate geometry to four equivalent Ho and two equivalent C atoms. Both B–C bond lengths are 1.60 Å. C is bonded in a 2-coordinate geometry to four equivalent Ho, two equivalent B, and one C atom. The C–C bond length is 1.42 Å.
36 MATERIALS SCIENCE↗
Materials Data on Ho(SiRu)2 by Materials Project
HoRu2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ho3+ is bonded in a 8-coordinate geometry to eight equivalent Si4- atoms. All Ho–Si bond lengths are 3.21 Å. Ru+2.50+ is bonded to four equivalent Si4- atoms to form a mixture of edge and corner-sharing RuSi4 tetrahedra. All Ru–Si bond lengths are 2.38 Å. Si4- is bonded in a 4-coordinate geometry to four equivalent Ho3+ and four equivalent Ru+2.50+ atoms.
36 MATERIALS SCIENCE↗