O2 Mixture Research Articles

Sensing Gas Mixtures by Analyzing the Spatiotemporal Optical Responses of Liquid Crystals Using 3D Convolutional Neural Networks.

We report how analysis of the spatial and temporal optical responses of liquid crystal (LC) films to targeted gases, when performed using a machine learning methodology, can advance the sensing of gas mixtures and provide important insights into the physical processes that underlie the sensor response. We develop the methodology using O3 and Cl2 mixtures (representative of an important class of analytes) and LCs supported on metal perchlorate-decorated surfaces as a model system. Although O3 and Cl2 both diffuse through LC films and undergo redox reactions with the supporting metal perchlorate surfaces to generate similar initial and final optical states of the LCs, we show that a three-dimensional convolutional neural network can extract feature information that is encoded in the spatiotemporal color patterns of the LCs to detect the presence of both O3 and Cl2 species in mixtures and to quantify their concentrations. Our analysis reveals that O3 detection is driven by the transition time over which the brightness of the LC changes, while Cl2 detection is driven by color fluctuations that develop late in the optical response of the LC. We also show that we can detect the presence of Cl2 even when the concentration of O3 is orders of magnitude greater than the Cl2 concentration. The proposed methodology is generalizable to a wide range of analytes, reactive surfaces, and LCs and has the potential to advance the design of portable LC monitoring devices (e.g., wearable devices) for analyzing gas mixtures using spatiotemporal color fluctuations.

Low-voltage-operation of flexible organic C8-BTBT thin-film transistors with a reactively sputtered AlOx gate dielectric

High-k dielectrics are frequently used for organic thin-film transistors (OTFTs), which facilitate the reduction of the device's operating voltage and enhance the total electrical performance. Along these lines, in this work, the fabrication of high-k AlOx dielectrics with high capacitance and low leakage current is proposed. On top of that, low-voltage flexible OTFTs with a solution-processed 2,7-dioctyl benzothieno[3,2-b] benzothiophene channel layer were demonstrated. The AlOx dielectric film was deposited by employing the reactive magnetron sputtering technique from a metal Al target by using a gas mixture of Ar and O2 at room temperature. At the same time, the surface morphology of the semiconductor film was optimized by controlling the solid solubility of polystyrene and polymethyl methacrylate in the semiconductor solution, which is important for improving the device performance. In this way, the prepared flexible OTFTs showed a low operating voltage of 3 V, a high switch ratio of 4.2 × 107, a high mobility is 2.39 cm2/V s, and a steep subthreshold swing close to the theoretical limit of 68 mV/decade. It is, thus, expected that this method will be applicable to the development of high-performance OTFTs.

Evolutions of repetitively pulsed positive streamer discharge in electronegative gas mixtures at high pressure

Electronegative gas components and gas pressure significantly change residual charge dynamics, which are critical for pulse-periodic streamer discharge behaviors. Evolutions of repetitively pulsed positive streamer discharge and the streamer-to-spark transitions were investigated at high pressures and compared between typical weak (O2) and strong (SF6) electronegative gas mixtures. Pulse-sequence resolved electrical and optical diagnostics were implemented to capture discharge evolutions in long pulse trains. We observe that streamer inception and propagation under subsequent pulses in N2 and N2–O2 mixtures are similar, including the earlier inception of the primary streamer and the accelerated propagation of the secondary streamer. The repetitively pulsed breakdown is extended to the low pulse repetition frequency region with the addition of O2. Discharge evolutions are unexpectedly different in N2–SF6 mixtures. Subsequent discharge channels prefer to propagate around the periphery of the inception cloud region with large radial deviations. Another difference is the precursor channel identified besides multiple streamer channels. Effects of electronegative gas on streamer evolutions under positive repetitive pulses have been qualitatively analyzed. Collisional electron detachment and photo-ionization are crucial in N2–O2 mixtures. With the presence of strong electronegative gas (SF6), the leader formation is probably induced by the earlier corona inception and longer voltage stressing period under following pulses in a pulse train, which are caused by the strong electronegativity of SF6 and the small ion mobility.

Numerical simulation of the influence of confined multi-point ignited H2–O2 mixture on the propagation of shock waves towards a deformable plate

The study of shock wave propagation in a detonation chamber is of great importance as a part of the plate forming process. Investigations related to the effects of premixed gas detonation on the deflection of a plate require in-depth examination. An Eulerian-Lagrangian numerical simulation is conducted using the space-time conservation element and solution element method of LS-DYNA software to study the effect of confined multi-point ignited gaseous mixture on the dynamic response of thin plates clamped at the end of a combustion chamber. The FSI couples a Lagrangian finite element solver with a Eulerian fluid solver in a 2D space with detailed chemistry of H2–O2 mixture. The solution contains the detonation wave propagation through the combustion chamber and its interaction with the plate. The influence of variation in the multi-point ignition locations and combustion chamber dimensions on the pressure history and plate deflection is studied. To verify the model, a comparison with the experimental study is carried out using an adjustable model representative of the real experiment. The verified model is used to link the evolution of plate shape with the arrival time and intensity of shock waves within the chamber. It is found that a longer distance between the ignition point and the plate intensifies the ultimate deflection of the plate. In addition, a fairly large combustion area employed in a direction rather than transverse to the plate surface is unable to influence the ultimate deformation of the plate.

Highly efficient preconcentration using anodically generated shrinking gas bubbles for per- and polyfluoroalkyl substances (PFAS) detection.

Here we report a highly efficient PFAS preconcentration method that uses anodically generated shrinking gas bubbles to preconcentrate PFAS via aerosol formation, achieving ~ 1400-fold enrichment of PFOS and PFOA-the two most common PFAS-in 20min. This new method improves the enrichment factor by 15 to 105% relative to the previous method that uses cathodically generated H2 bubbles. The shrinking gas bubbles are in situ electrogenerated by oxidizing water in an NH4HCO3 solution. H+ produced by water oxidation reacts with HCO3- to generate CO2 gas, forming gas bubbles containing a mixture of O2 and CO2. Due to the high solubility of CO2 in aqueous solutions, the CO2/O2 bubbles start shrinking when they leave the electrode surface region. A mechanistic study reveals two reasons for the improvement: (1) shrinking bubbles increase the enrichment rate, and (2) the attractive interactions between the positively charged anode and negatively charged PFAS provide high enrichment at zero bubble path length. Based on this preconcentration method, we demonstrate the detection of ≥ 70ng/L PFOA and PFOS in water in ~ 20min by coupling it with our bubble-nucleation-based detection method, fulfilling the need of the US Environmental Protection Agency.

Partial oxidation of methane to oxygenates by oxygen transfer at novel lattice oxygen sites of palladium and ruthenium bimetal oxide

Alumina-supported bimetal oxide (PdRuOx) catalysts were prepared by galvanic displacement reduction method for partial oxidation of methane into oxygenates, and evaluated in a fixed-bed reactor at relatively low temperatures of 280–310 °C, using a mixture of NO and O2 as the oxidant. The bimetal oxide catalysts exhibited high selectivity to HCHO. However, CO2 was dominantly obtained over two alumina-supported monometal oxide (PdO and RuO2) catalysts. Characterizations results showed that bimetal oxide-PdRuOx species with Pd-(O)-Ru active sites can selectively convert CH4 to HCHO through the transfer of its novel lattice oxygen. And in this process, CH3OH may play as an intermediate. Compared to oxidation with either O2 and NO, the mixture oxidant of NO and O2, acting as an oxygen shuttle through the gas-phase reaction of NO+1/2 O2→NO2, promoted the selective formation of HCHO.

A computational study of steady and stagnating positive streamers in N2–O2 mixtures

In this paper, we address two main topics: steady propagation fields for positive streamers in air and streamer deceleration in fields below the steady propagation field. We generate constant-velocity positive streamers in air with an axisymmetric fluid model, by initially adjusting the applied voltage based on the streamer velocity. After an initial transient, we observe steady propagation for velocities of 3 × 104 m s−1 to 1.2 × 105 m s−1, during which streamer properties and the background field do not change. This propagation mode is not fully stable, in the sense that a small change in streamer properties or background field eventually leads to acceleration or deceleration. An important finding is that faster streamers are able to propagate in significantly lower background fields than slower ones, indicating that there is no unique stability field. We relate the streamer radius, velocity, maximal electric field and background electric field to a characteristic time scale for the loss of conductivity. This relation is qualitatively confirmed by studying streamers in N2–O2 mixtures with less oxygen than air. In such mixtures, steady streamers require lower background fields, due to a reduction in the attachment and recombination rates. We also study the deceleration of streamers, which is important to predict how far they can propagate in a low field. Stagnating streamers are simulated by applying a constant applied voltage. We show how the properties of these streamers relate to the steady cases, and present a phenomenological model with fitted coefficients that describes the evolution of the velocity and radius. Finally, we compare the lengths of the stagnated streamers with predictions based on the conventional stability field.

Integration of molten carbonate fuel cell and chemical looping air separation for high-efficient power generation and CO2 capture

Molten carbonate fuel cell (MCFC) allows concentrating the CO2 from the cathode side to the anode side, generating electricity concurrently. Chemical looping air separation (CLAS) can produce an O2 and CO2 mixture stream as cathode feeding gas of MCFC. In this paper, a natural gas-fueled MCFC with internal reforming is integrated with CLAS as O2 and CO2 source for high-efficient power generation with CO2 capture. An O2 and CO2 mixture stream is produced from CLAS by recirculating a portion of CO2-rich flue gas after the afterburner to CLAS. The system is analyzed through thermodynamic and economic performance. At the baseline case, the plant net power efficiency is 59.5%, with 99.9% CO2 capture rate. Based on sensitivity analysis, the higher fuel cell temperature and fuel utilization factor can increase the plant net power efficiency, while the steam carbon ratio and the CLAS reduction reactor temperature are preferable to be at lower levels for higher plant net power efficiency. Finally, economic analysis is conducted. With a MCFC specific cost of $1327/kW and a natural gas price of $2.79/million Btu, the cost of electricity (COE) is $0.094/kWh. The results show the proposed system is attractive for natural gas-fueled power generation with CO2 capture.

Performance Projection of a High-Temperature CO2 Transport Membrane Reactor for Combined CO2 Capture and Methane-to-Ethylene Conversion

Direct conversion of methane into ethylene through the oxidative coupling of methane (OCM) is a technically important reaction. However, conventional co-fed fixed-bed OCM reactors still face serious challenges in conversion and selectivity. In this paper, we apply a finite element model to simulate OCM reaction in a plug-flow CO2/O2 transport membrane (CTM) reactor with a directly captured CO2 and O2 mixture as a soft oxidizer. The CTM is made of three phases: molten carbonate, 20% Sm-doped CeO2, and LiNiO2. The membrane parameters are first validated by CO2/O2 flux data obtained from CTM experiments. The OCM reaction is then simulated along the length of tubular plug-flow reactors filled with a La2O3-CaO-modified CeO2 catalyst bed, while a mixture of CO2/O2 is gradually added through the wall of the tubular membrane. A 12-step OCM kinetic mechanism is considered in the model for the catalyst bed and validated by data obtained from a co-fed fixed-bed reactor. The modeled results indicate a much-improved OCM performance by membrane reactor in terms of C2-yield and CH4 conversion rate over the state-of-the-art, co-fed, fixed-bed reactor. The model further reveals that improved performance is fundamentally rooted in the gradual methane conversion with CO2/O2 offered by the plug-flow membrane reactor.

Minute-Scale Synthesis of Nano Silicalite-1 Zeolites

Synthesis of zeolites in more efficient and greener methods is of great significance in both industrial and academic fields. However, the relative long time for zeolite crystallization and much consumption of water solvent make the target challengeable. Herein, a route for ultrafast synthesis of nano Silicalite-1 zeolites in 10 min with much less water consumption has been developed. Comprehensive characterizations, i.e., X-ray powder diffraction, N2 sorption, scanning electron microscope, and NMR, confirm the high quality of such obtained Silicalite-1 zeolites. In the catalytic deoxygenation of O2-containing ethylene (mixture of O2 and ethylene), these reported Silicalite-1 zeolite samples show the comparable performance with the conventional Silicalite-1 zeolites synthesized under hydrothermal conditions. This research therefore provides a new trial toward the ultrafast synthesis of zeolite materials in an environment-friendly route.

Periodical discharge regime transitions under long-term repetitive nanosecond pulses

Intuitively, the nanosecond repetitively pulsed (NRP) corona and spark regimes are sustained successively after onsets due to the high background electron density and/or the surplus heat. In this paper, the NRP discharge unexpectedly swings among different regimes (corona → glow → spark → corona → …) in one pulse train, which is characterized by the periodical spark quench and reestablishment. We have investigated discharge regime instabilities by applying long-term repetitive high-voltage nanosecond pulses of ∼15 ns duration to needle–needle and needle–plane gaps in atmospheric-pressure N2 and N2–O2 mixtures. Pulse-sequence resolved electrical and optical diagnostics have been implemented to capture transition processes. The initial corona gradually grows into glow and then spark ‘pulse-by-pulse’, however, the spark regime was interrupted after a certain number of voltage pulses until the next reestablishment. Narrow pulse width impedes the discharge instability growth within one pulse, and a certain number of voltage pulses are required for the discharge regime transition. The addition of O2 dramatically boosts the duration length of spark regime. A lower output impedance of the power supply induces a higher deposited energy into a spark, however, not necessarily leads to a longer spark regime duration, although both the energy storage and the average electric field strength are approximate. Polarity effects, conventionally diminished in pulse-periodic discharges, are still evident during the discharge regime transition. The periodical discharge regime transition is qualitatively explained based on the plasma–source coupling and the evolution trajectory along the power transfer curve. Feedback mechanisms and residual-conductivity related screening effect in NRP spark discharges are analyzed based on a simplified 0D simulation. The periodical feature is probably caused by the insufficient average deposited energy per unit distance per one pulse cycle. In-depth understandings of ‘non-binary’ regimes (neither corona nor spark) and memory effect mechanisms of NRP discharges could be reached.

Conversion of CO2 in a pulsed arc discharge

We present a study of CO2 gas conversion into a mixture of CO2, CO and O2 by means of a pulsed arc discharge at atmospheric pressure. The CO2 molecule is dissociated as a result of the interaction with the highly energetic electrons and excited species produced in the plasma domain. The plasma conversion of CO2 provides a relatively simple approach to CO2 conversion without the need of special materials required by chemical reactors. In this study, the discharge operates at atmospheric pressure, which leads to a reduced efficiency compared to the low pressure operation due to the additional electron losses via elastic collisions. The operation at atmospheric pressure, however, provides simplicity, robustness and low cost of the discharge system, which makes it very attractive from an industrial point of view. Further, we use a pulsed discharge, which, in comparison to the DC discharges, provides additional possibilities for optimizing the dissociation process by controlling precisely the energy input into the plasma. This is achieved by controlling the pulse repetition rate and duty ratio in addition to the discharge current and gas flow characteristics. We present results for the CO2 dissociation rate and energy efficiency for a wide range of different discharge parameters.

Adoption of the CO2 + SO2 mixture as working fluid for transcritical cycles: A thermodynamic assessment with optimized equation of state

This paper focuses on the use of the CO2 + SO2 binary mixture as innovative working fluid for closed transcritical power cycles with a minimum temperature above 50 °C. Starting from a literature review of the available experimental data on the mixture, the PC-SAFT EoS is identified as a suitable model to characterize the mixture behavior. Once the proper thermodynamic model is selected for this mixture, a comparison between the innovative transcritical cycle and the sCO2 cycle is proposed for various plant layouts in order to find out the advantages of the innovative mixture. The analysis is presented fixing the cycle maximum temperature at 700 °C and the maximum pressure at 250 bar: the results depict an increment in cycle electric efficiency and cycle specific work, along with a lower temperature of heat introduction in the cycle for any considered configuration of transcritical CO2 + SO2 cycle, when compared to pure sCO2.An economic analysis of the power block is then performed to support the selection of the innovative working fluid. Two of the most promising plant layouts are evidenced: the recompression layout is selected for highly efficient power blocks, while the dual recuperated layout works effectively in applications characterized by higher hot source exploitation. The recompression layout adopting the CO2 + SO2 mixture presents a power block electric efficiency of 48.67% (2.33% higher than the respective sCO2 cycle) and a reduction of the power block CAPEX from 1160 $/kWel to 1000 $/kWel when compared to the sCO2 configuration for a 100MWel size, while the dual recuperated layout exploiting the CO2 + SO2 mixture shows a power block electric efficiency of 39.58% (0.69% above the same sCO2 cycle), a decrease of power block CAPEX from 795 $/kWel to 718 $/kWel and 70 °C of additional heat recovery from the hot source with respect to the analogous sCO2 cycle.

Joint Redox Mechanism of Water Synthesis in H2 and O2 Mixture in the Presence of a Series of Metal Oxides

Joint Redox Mechanism of Water Synthesis in H2 and O2 Mixture in the Presence of a Series of Metal Oxides

Plasma assisted CO2 dissociation in pure and gas mixture streams with a ferroelectric packed-bed reactor in ambient conditions

Carbon dioxide decomposition is a challenging target to combat climate change. Nonthermal plasmas are advantageous for this purpose because they operate at ambient conditions and can be easily scaled-up. In this study, we attempt the CO2 splitting into CO and O2 in a parallel plate packed-bed plasma reactor moderated with Lead Zirconate Titanate (PZT) as ferroelectric component, achieving conversion rates and energy efficiencies higher than those obtained with BaTiO3 in our experimental device. The analysis of the reaction mechanisms with optical emission spectroscopy under various operating conditions has shown a direct correlation between energy efficiency and intensity of CO* emission bands. These results and those obtained with a LiNbO3 plate placed onto the active electrode suggest that high temperature electrons contribute to the splitting of CO2 through an enhancement in the formation of CO2+ intermediate species. Results obtained for CO2 + O2 mixtures confirm this view and suggest that back recombination processes involving CO and O2 may reduce the overall splitting efficiency. The study of mixtures of CO2 and dry air has proved the capacity of ferroelectric packed-bed reactors to efficiently decompose CO2 with no formation of harmful NXOY subproducts in conditions close to those in real facilities. The found enhancement in energy efficiency with respect to that found for the pure gas decomposition supports that new reaction pathways involving nitrogen molecules are contributing to the dissociation reaction. We conclude that PZT moderated packed-bed plasma reactors is an optimum alternative for the decompositon of CO2 in real gas flows and ambient conditions.

Thermodynamics of heterogeneous equilibria in the In-In2 O3 system using Knudsen effusion mass spectrometry.

The In-In2 O3 system is regarded as a potential low-temperature source of gaseous indium oxide (In2 O) when obtaining functional materials by physical vapor deposition techniques. To date the vaporization thermodynamics of the system have been investigated in few studies, the results of which are contradictory. The study of the In-In2 O3 system was performed using Knudsen effusion mass spectrometry in the temperature range 930-1210 K, with a magnet mass spectrometer (MS-1301). Quartz effusion cells heated by a resistance furnace were employed. It was established that In(g) and In2 O(g) are the major vapor species over heterogeneous mixtures (In(l) + In2 O3 (s)) and the gaseous oxide In2 O is predominant. The partial pressures of the vapor species were determined and the quantitative vapor composition was calculated. Based on the experimental data, a p-x section of the In-In2 O3 system phase diagram at 1060 K was constructed. The standard enthalpies of reactions accompanying vaporization of the In and In2 O3 mixtures were evaluated using the second- and third-law methods. The standard enthalpy of formation of In2 O(g) was derived from the enthalpies of reactions obtained. The predominance of In2 O in the equilibrium vapor over heterogeneous mixtures (In(l) + In2 O3 (s)), along with its high partial pressure at relatively low temperatures, substantiate the In-In2 O3 system to be suitable for physical vapor deposition methods. The obtained results can be used for physical vapor deposition parameter adjustment and optimization. The standard enthalpy of formation of In2 O(g) obtained in an independent way in the present work is in good agreement with that from our previous In2 O3 (s) vaporization study.

Phase formation, thermal stability and mechanical properties of Nb-B-C coatings prepared by combinatorial magnetron sputtering

In this study, combinatorial magnetron sputtering was used to deposit Nb-B-C coatings in a wide composition range. The phase formation, thermal stability and mechanical properties of these coatings were investigated in relation to their composition and deposition conditions. The studied coatings were amorphous, short range ordered or exhibited crystalline phases such as Nb, NbC and NbB2. Higher energy flux to the coating achieved by the use of bias and heating during deposition resulted in coatings being crystalline over a wider composition range. Annealing of the coatings after deposition resulted in a higher degree of crystallinity as well as an increase in hardness and effective elastic modulus. The hardness of the coatings was up to 22.5 ± 0.7 GPa before and up to 35.0 ± 0.6 GPa after annealing. The effective elastic modulus was up to 240 ± 10 GPa before and up to 310 ± 7 GPa after annealing. Coatings with a high B content exhibited the highest hardness and elastic modulus in both cases. Coating powder was prepared by sputtering a Nb2BC target and studied using differential scanning calorimetry. The powder exhibited a crystalline NbC phase before and after annealing up to 900 °C. The material was stable in an Ar atmosphere in the studied temperature range. In an Ar + O2 mixture, the powder was stable up to ~580 °C. At this temperature, an oxidation reaction started, resulting in the formation of Nb2O5.

Pollutant Emissions during Oxy-Fuel Combustion of Biomass in a Bench Scale CFB Combustor

Nowadays oxy-fuel combustion of coal and biomass is the most promising option for the reduction of CO2 emissions from power plants. In this paper, emissions of NOx (NO, NO2, N2O and their precursors, such as NH3 and HCN), SO2 and CO during conventional and oxy-fuel combustion of three kinds of biomass (agro, woody and energy crop) and a reference coal are presented and discussed. Combustion tests were conducted at 850 °C in the laboratory-scale circulating fluidized bed (CFB) reactor in air and O2/CO2 atmospheres. A FTIR spectrometer was used to measure instantaneous concentrations of all pollutants in the flue gas. Emissions of SO2, N2O and CO for the combustion of biomass in all atmospheres were lower than those for the combustion of reference coal. It was found that oxidation of nitrogen species released with volatile matter was responsible for high emissions of NOx during combustion of biomass fuels in air and mixtures of O2 and CO2. The lowest NO emissions for tested fuels were detected in oxy-21 atmosphere (21% O2/70% CO2). Oxy-combustion of biomass in O2/CO2 mixtures at 30% and 40% O2 caused a decrease in emissions of N2O and CO while NO and SO2 emissions increased. The results of this study show that the tested biomass fuels are ideal renewable energy resources both in conventional and oxy-fuel conditions with a minor potential for environmental pollution.

Spectrally-resolved ultraviolet absorption measurements of shock-heated NO from 2000 K to 6000 K for the development of a two-color rotational temperature diagnostic

In high-enthalpy air flows, nitric oxide (NO) formation and removal involves multiple, complex energy transfer processes that occur under nonequilibrium conditions, thus motivating the need for diagnostic methods to probe such flows in laboratory settings. In this work, a rotational temperature diagnostic for NO was developed using a spectroscopic model (Stanford NO model) of the γ-bands of NO to inform optimal wavelength candidates for absorption using two continuous-wave (CW), ultraviolet (UV) lasers. Absorption cross-sections of shock-heated NO were measured with two CW UV lasers over a range of temperatures and wavelengths, and results were compared to the Stanford NO model. All measurements were completed behind reflected shocks in 0.4% and 2% mixtures of NO in argon (Ar). Fixed-wavelength cross-section measurements from 2000 K to 6000 K between 1 atm to 0.085 atm were made at nominal wavelengths of 226.1026 nm and 224.8155 nm. Additionally, fixed-temperature measurements were made over the wavelength range 226.1013 nm to 226.1035 nm at 0.8 atm. The combination of experiments provided temperature and wavelength sweep cross-sections to compare against the Stanford NO model. The formulation for the collisional broadening parameter, 2γ, was divided into two temperature regimes, transitioning at 2500 K. Additionally, line positions of the R11(26.5), R12(34.5), Q21(26.5), and Q22(34.5) transitions around 224.8155 nm and the Q11(12.5), R12(19.5), P21(12.5), and Q22(19.5) transitions around 226.1026 nm were adjusted to best fit the cross-section data. A vibrational equilibrium assumption was used to determine the translational and vibrational temperatures at the point of cross-section determination, while a coupled vibration-dissociation (CVDV) model characterized the extent of dissociation at the point of cross-section determination. Data from both temperature-sweep and wavelength-sweep measurements agree to within ± 10% of the Stanford NO model, with most cross-sections falling within ± 5% of model predictions. Oxygen (O2) cross-sections measurements were also taken behind reflected shocks in dilute 2% O2 in Ar mixtures at 2000 K and 6000 K to quantify the interfering O2 absorbance at the chosen diagnostic wavelengths.

Mechanisms for sonochemical oxidation of nitrogen.

N2O, and mixtures of N2 and O2, dissolved in water-both in the presence and absence of added noble gases-have been subjected to ultrasonication with quantification of nitrite and nitrate products. Significant increase in product formation upon adding noble gas for both reactant systems is observed, with the reactivity order Ne < Ar < Kr < Xe. These observations lend support to the idea that extraordinarily high electronic and vibrational temperatures arise under these conditions. This is based on recent observations of sonoluminescence in the presence of noble gases and is inconsistent with the classical picture of adiabatic bubble collapse upon acoustic cavitation. The reaction mechanisms of the first few reaction steps necessary for the critical formation of NO are discussed, illustrated by quantum chemical calculations. The role of intermediate N2O in this series of elementary steps is also discussed to better understand the difference between the two reactant sources (N2O and 2 : 1 N2 : O2; same stoichiometry).