First-principles study of crystal structures of NO+NO3− under pressure

First-principles calculations employing density functional theory are performed to study ionic crystal structures of NO⁺NO₃^?. The pressure dependences of enthalpy, structural parameters, and electronic band gap are investigated for the two experimentally reported phases of NO⁺NO₃^?. It is found that these two phases have comparable densities for P<25 GPa and are thus competing ones that may be obtained through different pathways. Moreover, one of the two phases is unlikely the previously proposed orthorhombic P2₁cn structure. The trend of pressure dependence of the band gap is typical of that for ionic crystals. This study provides insight into different experimental findings.     

Magnetic Faraday modulation spectroscopy of the 1–0 band of 14NO and 15NO

Magnetic rotation spectroscopy signals of the nitric oxide (NO) fundamental band near 5 μm have been observed and compared with calculated signals. This spectroscopic approach exploits magnetic field modulation in the Faraday configuration for very sensitive detection of NO. Line shapes and strengths of the Faraday signals depend on molecular parameters, like J and Ω quantum numbers of the transitions involved, and on experimental parameters, like pressure of the gas sample and applied external magnetic field strength. In this study we implemented a software model which provides a simulation of the complete v=1–0 Faraday spectrum of NO. The algorithm considers the magnetic field modulation, the collisional and Doppler broadening of the line shapes, and the line intensities of ¹⁴NO and ¹⁵NO fundamental band lines. Optimum values for pressure and magnetic field modulation for maximum sensitivity are given. Suitable spectral windows for simultaneous detection of ¹⁴NO and ¹⁵NO are discussed. Experimental data were obtained in the wavenumber region from 1840 to 1900 cm^?1 by means of a CO sideband laser and a quantum cascade laser. Comparison between calculated and observed signals shows excellent agreement.     

Spin splittings in the ν3 band of NO2

Spin splittings for several important atmospheric lines in the ν₃ band of NO₂ have been measured by diode laser. An improved spin-splitting program has been developed which takes into account the asymmetry effects in the lower K_a splittings. The measured spin splittings and the derived spin-rotational constants are reported in this study to a much higher accuracy than previously achieved.     

Dynamic modelling and simulation of ¹⁵N separation by chemical exchange in NO, NO₂-HNO₃ system

The dynamic behaviour of a 1?N separation process by chemical exchange in a NO, NO?-HNO? system has been analysed based on an accurate mathematical model. A nonlinear system of first-order partial differential equations was determined by considering the multiple exchange reactions between the components of the gaseous mixture and the liquid phase constituents. The mathematical model of the process describes the space-time variation of the 1?N mole fraction in gas and liquid phases and provides a better understanding of operating limits and decision support in process design and optimisation.     

Removal of NO Molecules by a Novel Atmospheric Pressure Plasma Apparatus

A novel atmospheric pressure plasma apparatus （APPA） is designed with a liquid electrode, and its discharging characteristics are studied. Relatively uniform and intense discharge can be realized in the APPA system. An experimental study on removal of NO molecules is carried out by using the APPA, and more than 95.5% of NO is decomposed when the NO initial concentration is lower than 400ppm. Removal of NO efficiency increases rapidly with the increasing discharge power. Compared with the absence of O2, more NO2 is generated with the increase of O2 concentration. However, most of the NO molecules are decomposed to N2 and O2 directly, when O2 concentration changes from 0 to 1.1 vol%.     

Dynamic modelling and simulation of 15N separation by chemical exchange in NO,NO2–HNO3 system

The dynamic behaviour of a ¹⁵N separation process by chemical exchange in a NO, NO₂–HNO₃ system has been analysed based on an accurate mathematical model. A nonlinear system of first-order partial differential equations was determined by considering the multiple exchange reactions between the components of the gaseous mixture and the liquid phase constituents. The mathematical model of the process describes the space–time variation of the ¹⁵N mole fraction in gas and liquid phases and provides a better understanding of operating limits and decision support in process design and optimisation.     

A model for temperature-dependent collisional quenching of NO A2 Σ+

A model for the temperature-dependent electronic quenching of NO A ^{2 +} is presented. The model is appropriate for collision partners having stable negative ions, which are predicted to have large quenching cross-sections. Colliders with relatively large negative electron affinities are predicted to have cross-sections that are near-zero at room temperature and can increase dramatically at very high temperatures. A negligibly small electronic quenching cross-section is predicted for collision partners having negative ions that are unstable on a collisional timescale. Results of the model are compared to experimentally measured cross-sections for a number of species of interest in combustion and aerothermodynamic applications.     

Theoretical study on the reaction of CH3CHCl + NO2

The detailed reaction mechanism of 1-chloroethyl radical with NO₂ is investigated theoretically. The results show that the title reaction is more favourable on the singlet potential energy surface than on the triplet one. For the singlet PES of CH₃CHCl?+?NO₂, it is shown that the CH₃CHCl radical can react with NO₂ to barrierlessly generate adduct a (H₃CHClCNO₂), b₁ (H₃CHClCONO-trans), and b₂ (H₃CHClCONO-cis), respectively. A total of six energetically reaction pathways and ten products are found. However, the most competitive path way is P₁ (CH₃CHO?+?ClNO), which can further dissociate to give P₆ (CH₃CHO?+?Cl?+?NO) and P₂ (CH₃CClO?+?HNO). The present results can lead to a deep understanding of the mechanism of the title reaction and may be helpful for understanding the halogenated ethyl chemistry.     

Laser-Induced Continuum Structure of NO Molecules in Two-Colour Femtosecond Pulsed Laser Fields

The method of quantum wave packet dynamics is used to study the multiphoton ionization of NO molecules via a two-photon Raman coupling and a laser-induced continuum structure （LICS） state in two-colour strong femtosecond pulsed laser fields. Time-and energy-resolved photoelectron energy spectra are calculated for describing three photoionization channels. The population transfers through the LICS and the Raman coupling passages are discussed.     

Resonance-enhanced multiphoton ionization of NO via X~2II-A~2Σ transition

The resonance-enhanced multiphoton ionization (REMPI) spectrum of NO has been obtained in the range of 420 - 480 nm with a Nd:YAG pumped optical parametric generator and amplifier. The spectral lines can be attributed to NO X2II(v=0,1)-A2(v' = 0,1) transitions. In this wavelength range, NO molecules are ionized via the resonant intermediate state A2E+ and by a (2 + 2) REMPI process. The dependence of ion signals on laser intensity and gas pressure is discussed. The variation of the ionization signal versus laser intensity is near quartic. This is in good agreement with theory.     

Laser-induced fluorescence decay lifetimes of shock-heated NO (A 2Σ+)

Radiative emission in the NO -band system occurs when air at a few Torr initial pressure is shock-heated at sufficiently high temperatures of 3500–7000 K. Emission spectra of this system in shocks indicate that collisional quenching of the emitting A ²⁺ state is a critical quantity controlling the intensity. Quenching of excited NO by NO itself has been measured using direct time decay of laser-induced fluorescence in the shock tube at 3500 K. The cross section (2– error) is 59±20 Ų, compared to the room temperature value 37±8 Ų. At 3500 K, N₂ also quenches NO with a cross section 2 Ų, much larger than the value at 300 K.Sabbatical visitor, on leave from DLR Stuttgart, Fed. Rep. Germany     

Sonochemical nitrogen fixation for the generation of NO2− and NO3− ions under high-powered ultrasound in aqueous medium

Sonochemical species such as nitrite (NO₂⁻) and nitrate (NO₃⁻) were detected in ultrapure aqueous medium with 28 kHz low frequency ultrasound (US) in the range of 200–1200 W output power. The concentration of their anionic ions monitored with a high-performance liquid chromatography increased with increasing US power especially under air atmosphere. When the generation of NO₂⁻ and NO₃⁻ ions under US exposure was investigated for N₂, O₂ and Ar-bubbled solutions, no trace of NO₂⁻ was observed while NO₃⁻ was slightly generated. Under air atmosphere, the concentration of dissolved oxygen in the aqueous medium increased especially when 1200 W power was used. In addition, the bulk pH shifted towards the acidic side with an increase in exposure time, which indicated that NO₂⁻ was formed. The formation of oxidizing species under 28 kHz low frequency ultrasonic treatment was confirmed with an absorption spectrum which was dominated by two maxima peaks at 288 nm and 352 nm representing triiodide I₃⁻ anion.     

Incoherent broad-band cavity-enhanced absorption spectroscopy for simultaneous trace measurements of NO2 and NO3 with a LED source

In the past decade, due to a growing awareness of the importance of air quality and air pollution control, many diagnostic tools and techniques have been developed to detect and quantify the concentration of pollutants such as NO _x , SO _x , CO, and CO₂. We present here an Incoherent Broad-Band Cavity-Enhanced Spectroscopy (IBB-CEAS) set-up which uses a LED emitting around 625 nm for the simultaneous detection of NO₂ and NO₃. The LED light transmitted through a high-finesse optical cavity filled with a gas sample is detected by a low resolution spectrometer. After calibration of the spectrometer with a NO₂ reference sample, a linear multicomponent fit analysis of the absorption spectra allows for simultaneous measurements of NO₂ and NO₃ concentrations in a flow of ambient air. The optimal averaging time is found to be on the order of 400 s and appears to be limited by the drift of the spectrometer. At this averaging time the smallest detectable absorption is 2×10⁻¹⁰ cm⁻¹, which corresponds to detection limits of 600 pptv for NO₂ and 2 pptv for NO₃. This compact and low cost instrument is a promising diagnostic tool for air quality control in urban environments.     

UV and 532 nm Photo-Dissociation of 2-Nitrotoluene: Observation of Electronically-Excited NO; Emission from Carbon (I); N2–NO Energy Transfer; and Stabilization of 2-Nitrotoluene-Ar Clusters

2-nitrotoluene is a taggant used in explosive compounds and also often used as a simulant for nitro-based high explosives. Various spectroscopic techniques focus on the detection of vibrationally excited NO as an indicator for the presence of explosives. We report on the photo-dissociation of 2-nitrotoluene using UV and 532 nm wavelengths. We not only observe vibrationally excited NO in its electronic ground state, but also vibrationally excited NO in its electronic excited state. The photo-dissociation of 2-nitrotoluene leads to the formation of atomic carbon and its emission, overlapping the NO emission, is observed. Energy transfer from laser-excited nitrogen to NO leads to NO emission with long lifetimes. Argon atoms stabilize 2-nitrotoluene molecules and delay their photo-dissociation.     

Cavity-ring-down spectroscopic studies of NO2 in the region around 613 nm

Catalytic degradation and diffusion processes of NO₂ were followed by cavity-ring-down spectroscopy (CRDS) at 612.9 nm. The suitability of this absorption method for quasi-continuous, direct quantitative measurements over extended periods of time is demonstrated. The high sensitivity of the method is reflected by the fact that NO₂ concentrations as low as 200 ppb were detected at wavelengths at which the absorption of NO₂ is 12-fold lower than at the absorption maximum at 413 nm. Absorption coefficients of less than 1×10^-7 cm^-1 were measured. Received: 25 February 2000 / Revised version: 4 August 2000 / Published online: 5 October 2000     

Resonance-enhanced multi-photon ionization spectrum of NO in 575-680 nm wavelength region

The multi-photon ionization spectrum of NO in the wavelength region of 575-680 nm is obtained with an optical parameter generator and amplifier (OPG/OPA) pumped by a picosecond Nd:YAG laser as radiation source. The banded structure of the spectrum indicates that NO molecule is ionized in resonant manner and the peaks of the spectrum are assigned to the transition of NO molecule from the ground electronic state to A2∑(v' = 0,1,2,3), E2∑(v' = 0,1,2), F2Δ(v' = 0,1,2,3) and H2∑(v' = 0,1,2) intermediate resonant ones. The molecule constants about NO (A2∑, E2∑, F2Δ, H2∑) states are calculated from the center wavelength of the spectrum. It is also found that owing to the special electron configuration of NO, this molecule does not follow the normal transition selection rule of the diatomic molecule during the multi-photon process.     

NO,NO2超精细LMR谱的观测

采用内腔CO激光磁共振光谱方法和微机数据采样系统,观测到了NO,NO₂分子的超精细激光磁共振(LMR)谱,简述了测量原理,给出了实验结果。     

Density functional theory study of NO2-sensing mechanisms of pure and Ti-dopedWO3 （002） surfaces

Density functional theory (DFT) calculations are employed to explore the NO₂-sensing mechanisms of pure and Ti-doped WO₃ (002) surfaces. When Ti is doped into the WO₃ surface, two substitution models are considered: substitution of Ti for W_6c and substitution of Ti for W_5c. The results reveal that substitution of Ti for 5-fold W forms a stable doping structure, and doping induces some new electronic states in the band gap, which may lead to changes in the surface properties. Four top adsorption models of NO₂ on pure and Ti-doped WO₃ (002) surfaces are investigated: adsorptions on 5-fold W (Ti), on 6-fold W, on bridging oxygen, and on plane oxygen. The most stable and likely NO₂ adsorption structures are both N-end oriented to the surface bridge oxygen O_1c site. By comparing the adsorption energy and the electronic population, it is found that Ti doping can enhance the adsorption of NO₂, which theoretically proves the experimental observation that Ti doping can greatly increase the WO₃ gas sensor sensitivity to NO₂ gas.     

Removal of NOx from NO2∶NO∶N2 mixture by a pulsed and dc streamer corona in a needle-to-plate reactor

The results of laboratory experiments on reduction of NO _x in the oxygen free gas mixture NO₂NON₂ simulating exhaust gas, by means of pulsed and dc streamer corona discharges generated in a needle-to-plate reactor have been presented. The results show that the dc corona discharge is more efficient in De-NO _x process than the pulsed corona discharge. This is in contrast to the results obtained in the wire-to-cylinder reactors where the pulsed corona discharge removes NO _x more efficiently. The results also lead to the conclusion that in the dc streamer corona discharge the short pulses and long interelectrode distances are recommended in order to increase the NO _x conversion rate.Presented at 17^th Symposium Plasma Physics and Technology, Prague, June 13–16, 1995.This work was financially supported by the Polish Academy of Sciences (projects IMP 3.1 and 3.3) and by the Polish Committee for Scientific Research (KBN Grant No. P40103304).