Nitrogen-15 Fractionation in the Thermal Decomposition of Nitrous Oxide of Natural Isotopic Composition

Abstract

The ¹⁵N fractionation in the thermal decompostion of nitrous oxide (N₂O) of natural isotopic composition has been investigated in quartz reaction vessel in the temperature interval 888–1073K. The formulas relating the observed experimentally ¹⁵N fractionations with the primary ¹⁵N kinetic isotope effect, (k ¹⁴/k ¹⁵)_p for ¹⁴N¹⁵N¹⁶O, and secondary ¹⁵N kinetic isotope effect, (k ¹⁴/k ¹⁵)_s for ¹⁵N¹⁴N¹⁶O, have been derived. The experimentally estimated ¹⁵N kinetic isotope effects have been compared with the primary and secondary ¹⁵N kinetic isotope effects calculated with the absolute rate theory formulations applied to linear three atom molecules. A good agreement was found for the primary ¹⁵N kinetic isotope effect, (k ¹⁴/k ¹⁵)_p, in the temperature interval 888–1007K. But at 1073K the decompositions of N₂O, accompanied by NO (nitric oxide) formation proceed with a twice times smaller primary kinetic isotope effect, (k ¹⁴/k ¹⁵)_p of 1.0251 ± 0.0009, only, suggesting the nonlinear transition state structures with participation of the fourth external atom at high temperature decompositions of nitrous oxide. The nitrogen isotope effects determined in this study correlate well with nitrogen isotope fractionations observed in the natural biological, earth and atmospheric processes.     

红外高光谱资料AIRS反演晴空条件下大气氧化亚氮廓线

N₂O是一种非常重要的温室气体和臭氧损耗物。由于观测资料有限,对于N₂O在这两方面所发挥的作用定量描述还存在很多的不确定性。利用热红外卫星数据AIRS可以反演监测甲烷和二氧化碳气体,但对氧化亚氮的反演还很少见到。因此该工作首次在国内针对高光谱红外卫星资料AIRS,开展利用最优估计法反演大气N₂O廓线的模拟研究。讨论了先验廓线的获取方法及反演通道的选取方法,并将反演结果和HIPPO飞机观测数据进行比较,发现AIRS观测数据可以很好的捕获N₂O的垂直分布,在300～900 hPa,与HIPPO数据趋势一致,且反演精度较高,相对误差仅为0.1%,与所选取反演通道的jacobian峰值区间一致。反演结果相比于特征向量统计法也有显著提高。     

中国地区氧化亚氮浓度时空变化特征分析

氧化亚氮是一种重要的温室气体和臭氧损耗物。利用热红外反演大气温湿廓线,由于大气氧化亚氮含量较少且变化幅度不大,一般都当作常量处理。但是在反演氧化亚氮时,由于大气温湿廓线和地表温度等参数相对氧化亚氮变化较大,可能很小的扰动就会覆盖掉氧化亚氮的吸收信号。因此有必要在上千个通道中,选取信噪比最高的通道,反演分析氧化亚氮浓度的时空变化特征,进而掌握我国氧化亚氮浓度的变化规律,为研究我国氧化亚氮排放对气候变化的贡献,制定合理的氧化亚氮减排政策等,提供可靠数据支撑。采取一种优化后的最优敏感廓线通道选取法,利用AIRS数据,基于最优估计法反演氧化亚氮浓度,与TCOON观测网中加拿大站点进行比对,结果显示卫星遥感与地面观测结果一致性较好,相关系数r为0.73,该算法可以推广到IASI和CrIS等热红外高光谱数据,使对氧化亚氮的观测数据增加到20多年,这种长时间序列的产品是对目前地面观测的有效补充。在氧化亚氮反演验证的基础上分析了我国氧化亚氮的年均值变化和月均值变化情况,以及它的空间分布特征。时空变化结果显示,我国氧化亚氮浓度在低纬度地区浓度相对较高,每年在华南地区的夏季达到峰值,月度间变化幅度较大,相比于月度变化,年度之间的变化幅度相对较小。监测结果同时显示,印度、巴基斯坦等国在紧邻我国地区,夏季氧化亚氮浓度较高,因此我国氧化亚氮浓度的时空变化特征除本地排放贡献外,也有一定的外部区域传输影响。     

N2O在142.5-147.5 nm射流冷却吸收光谱揭示的解离动力学

在射流冷却分子束下, 测量了142.5～147.5 nm N₂O分子C^{1∏态的吸收光谱,观测到清晰的振动序列结构,振动频率间隔约为500 cm-1. 结合理论计算的电子态势能面结构,这个振动序列被标识为解离电子态C1∏的弯曲振动激发. 傅立叶变换得到了相应的轨道周期为65 fs,而通过Lorentzian线型拟合获得了各振动峰对应的能级寿命约为20 fs.}     

基于长光程的土壤氧化亚氮排放规律的FTIR光谱法研究

氧化亚氮（N₂O）的过量排放会对臭氧层造成破坏,合理施肥和采取减排措施对减缓温室效应具有重要的现实意义。本文利用FTIR光谱法研究了施肥和水分对白菜地土壤排放N₂O的影响。为了提高系统的灵敏度,我们利用多个反射镜加长了光程。通过比对施肥前后N₂O红外光谱和NIST谱库N₂O红外光谱,最终选取2 160～2 225 cm-1作为定量计算N₂O的特征波段。研究发现,施肥和水分能促进白菜地土壤N₂O气体排放,这为农田N₂O的减排和减缓温室效应提供了理论依据。最后,还研究了施肥后土壤N₂O的昼夜排放规律,结果表明,N₂O白天的排放量高于晚上,通过和前人研究结果对比,验证了此方法的可行性。本文研究证实,基于长光程的FTIR光谱法是一种测量土壤排放N₂O气体规律的快速有效方法,它可以对施肥后的白菜地土壤N₂O气体排放进行测量,相对其他传统测量方法具有高速、简便等优势。     

15N Isotopic Effects on the Raman Spectra of Tribromoacetamide

Abstract

¹⁵N-Tribromoacetamide has been synthesized with an isotopic content of 99, 4%, its Raman spectra have been recorded in the range 4.000–50 cm^?1. The isotopic shifts arising from ¹⁵N have been determined and interpreted. We have assigned the vibrational spectra of Br₃CCONH₂ and some overtones, combinations and difference bands. The molecular structure of tribromoacetamide has been studied employing the Ab Initio teoretical calculations and the Teller - Redlich isotopic product rule has been applied by assuming these geometrical parameters:

rCN = 1.4623 Å, rCC = 1.6014 Å, rBrC = 1.9468 Å, rCO = 1.2144 Å, rNH = 1.0292 Å, C-C-Br = 108.83320, C-C-0:118.2440, C-C-N:120.4137, C-N-H:110.45930     

15N Distribution in Wheat and Chemical Fractionation of Root-Borne 15N in the Soil

Abstract

Spring wheat plants were grown in split-root containers and labelled with ¹⁵N by fertilizing one compartment of the container with ¹⁵NH₄ ¹⁵NO₃ (95 at.-% ¹⁵N exc.). After the harvest, approx. 90% of the ¹⁵N incorporated by the plants were found in the shoots and 3% in the roots; approx. 7% had been released into the soil of the unlabelled compartment. The ¹⁵N in the soil of the unlabelled compartment was extracted with KCl and hydrolysed with HCl. Approx. 60% of the ¹⁵N was found in the hydrolysable organic N pool of the soil and 9% in the fraction of the soluble and exchangeable inorganic nitrogen.     

Nitrous oxide conversion in laminar premixed flames of CH4 + O2 + Ar

Experimental measurements of the adiabatic burning velocity in neat and NO formation in CH₄ + O₂ + Ar flames doped with small amounts of N₂O are presented. The oxygen content in the oxidizer was varied from 15 to 17%. Non-stretched flames were stabilized on a perforated plate burner at 1 atm. The Heat Flux method was used to determine burning velocities under conditions when the net heat loss of the flame is zero. Adiabatic burning velocities of methane + oxygen + argon mixtures were found in satisfactory agreement with the modeling. The NO concentrations in the flames doped with N₂O (100 ppm in the argon stream before mixing) were measured in the burnt gases at a fixed distance from the burner using probe sampling. Axial profiles of [NO] were found insensitive to the downstream heat losses. Experimental dependencies of [NO] versus equivalence ratio had a maximum between φ = 1.1 and 1.2. Calculated concentrations of NO were in good agreement with the measurements. In lean flames calculated concentrations of NO strongly depends on the rate constant of reaction N₂O + O=NO + NO if too high values proposed in the literature are employed. These new experimental data thus allowed for validation of the key reactions of the nitrous oxide mechanism of NO formation in flames.     

Dynamics of 15N natural abundance in wood-decomposing fungi and their ecophysiological implications

Nine species of basidiomycota and one species of ascomycota were grown in an ammonium sulphate media and on beech wood; and the general ¹⁵N dynamic patterns of the hyphae were examined. The fungal body initially became depleted in ¹⁵N in both the types of incubation. However, the underlying mechanisms were quite different, that is, significant fungal ¹⁵N drop on the beech wood is associated with the fungal N reallocation and the uptake of atmospheric ammonia and/or NO_x, in addition to isotope fractionation during assimilation. Although the ¹⁵N values of the wood-decomposing basidiocarps were generally close to the ¹⁵N values of the wood, it does not always indicate that the wood derived N was the sole N source for the fungi throughout the growth periods as shown in our wood-decomposing experiment.     

Quantum cascade laser spectroscopy of N2O in the 7.9 μm region for the in situ monitoring of the atmosphere

A quantum cascade laser spectrometer was used in the Groupe de Spectrométrie Moléculaire et Atmosphérique of Reims (France) to precisely study nitrous oxide (N₂O) line parameters near 7.9 μm. The spectral region ranging from 1275 to 1280 cm^-1, which is suitable for the in situ measurement of N₂O in the atmosphere from balloon-borne measurements, was studied using a commercial laser from Alpes Lasers. Five lines of the ν₁ band of N₂O have been studied. The results of intensity measurements, air-broadening coefficients and their variation with temperature from −58 °C up to ambient temperature are compared with previous determinations and available databases. These results demonstrate that these parameters for N₂O are quite well known in the literature. Parameters obtained in this work are given with a very high precision.     

Fourier-transform spectroscopy of NNO in the 3500-9000 cm region

The Fourier-transform absorption spectrum of ¹⁵N¹⁴N¹⁶O-enriched nitrous oxide has been recorded at the Doppler limited resolution in the spectral range 3500-9000 cm⁻¹. More than 15 000 transitions of ¹⁵N¹⁴N¹⁶O were observed and assigned based on the global effective Hamiltonian model. The band-by-band analysis led to the determination of the ro-vibrational parameters of a total of 133 bands. Among these bands, 103 were newly observed, and the rotational analysis of 30 others were significantly extended and improved.     

Enrichment of the nitrogen atomic component with the <Superscript>15</Superscript>N isotope in a post-discharge zone

Isotope atomic composition in the post-discharge zone of a pulsed discharge in a nitrogen flow was studied by electron paramagnetic resonance. It is shown that, while the atomic concentration in the post-discharge zone decreases, the relative content of the ¹⁵N isotope increases more than 30 times compared to its natural abundance. Such a high isotope enrichment exceeds more than fourfold the corresponding maximal value that is predicted for the nitrogen atoms by the existing theoretical model. Analysis of the experimental results shows that the isotope-selective dissociation of nitrogen molecules proceeds in the post-discharge zone after the most part of atoms created in the discharge zone had recombined at the tube surface. A mechanism that explains that a nitrogen isotope enrichment as high as that is quite possible is proposed.     

High-resolution infrared spectroscopy of NNO and NNO in the 1200–3500 cm region

We present a continuation of our investigation of the second most abundant isotopic species of nitrous oxide, ¹⁴N¹⁵N¹⁶O and ¹⁵N¹⁴N¹⁶O, in the infrared (IR). Our two previous contributions looked at the 3500–9000 cm⁻¹ region for ¹⁴N¹⁵N¹⁶O and ¹⁵N¹⁴N¹⁶O, respectively, in the 3500–9000 cm⁻¹ region. The use of highly enriched isotopologue samples in this study allowed us to go further into the IR, down to 1200 cm⁻¹. A total of 2 2742 transitions have been assigned based on the effective Hamiltonian model, with 108 of them being reported here for the first time. Rovibrational analyses of 98, 101, 8, 3, 6, 1 and 1 bands for the ¹⁴N¹⁵N¹⁶O, ¹⁵N¹⁴N¹⁶O, ¹⁵N¹⁵N¹⁶O, ¹⁴N¹⁵N¹⁸O, ¹⁵N¹⁴N¹⁸O, ¹⁴N¹⁵N¹⁷O and ¹⁵N¹⁴N¹⁷O isotopologues, respectively, were also performed.     

The position dependent 15N enrichment of nitrous oxide in the stratosphere.

The position dependent 15N fractionation of nitrous oxide (N2O), which cannot be obtained from mass spectrometric analysis on molecular N2O itself, can be determined with high precision using isotope ratio mass spectrometry on the NO+ fragment that is formed on electron impact in the source of an isotope ratio mass spectrometer. Laboratory UV photolysis experiments show that strong position dependent 15N fractionations occur in the photolysis of N2O in the stratosphere, its major atmospheric sink. Measurements on the isotopic composition of stratospheric N2O indeed confirm the presence of strong isotope enrichments, in particular the difference in the fractionation constants for 15N14NO and 14N15NO. The absolute magnitudes of the fractionation constants found in the stratosphere are much smaller, however, than those found in the lab experiments, demonstrating the importance of dynamical and also additional chemical processes like the reaction of N2O with O(1D).     

The Role of Silicon Oxide Layers in Luminescence of Ensembles of Silicon Quantum Dots

Based on the quantum confinement-luminesecence center model,to ensembles of spherical silicon nanocrystals (nc-Si)containg two kinds of luminescence centers(LCs) in the SiOx layers surrounding the nc-Si,the relationship between the photolumincescence(PL) and the thickness of the SiOx layer is studied with the excitation energy flux density as a parameter.When there is no SiOx layer surrounding the nc-Si,the electron-heavy hole pair can only recombine inside the nc-Si,then the PL bluehift with reducing particle sizes roughly accords with the rule predicted by the quantum confinement model of Canham.When there presences a SiOx layer,some of the carriers may tunnel into it and recombine outside the nc-Si at the LCs to emit visible light.The thicker the SiOx layer is,the higher the radiative recombination rate occurred outside the nc-Si will be.When the central Scale of the nc-Si is much smaller than the critical scale,the radiative recombination rate outside the nc-Si dominates,and visible PL will be possible for some nc-Si samples with big average radius,greater than 4nm,for example.When there is only one kind of LC in the SIOx layer,the PL peak position does not shift with reducing particle sizes.All these conclusions are in accord with the experimental results.When there are two or more kinds of LCs in the SiOx layer,the PL peak position energy and intensity swing with reducing particle sizes.     

交流电沉积法制备金属氧化物纳米材料及形貌控制

以不同种类的金属丝为电极,采用交流电沉积的方法在液相水溶液中制备了多种金属氧化物纳米材料,并对其形貌进行了控制。由XRD和TEM分析结果表明,在相同的NaCI电解质水溶液中,不同的金属电极对应的不同金属氧化物纳米产物具有明显不同的形貌。     

Fourier transform spectroscopy of N2O weak overtone transitions in the 1-2 μm region

The absorption spectrum of the natural sample of nitrous oxide has been recorded at Doppler limited resolution with a Fourier-transform spectrometer in the spectral range 5000-10 000 cm⁻¹. Ten cold bands (8Σ − Σ and 2Σ − Π), thirteen hot bands (11Π − Π, Σ − Σ, and Δ − Δ) of ¹⁴N₂¹⁶O and the 3ν₃ band of ¹⁴N¹⁵N¹⁶O have been newly detected. The uncertainty of the line position determination is estimated to be about 0.005 cm⁻¹ for unblended lines. The assignment of the spectrum has been done with the help of the prediction performed within the framework of the polyad model of effective Hamiltonian. The spectroscopic parameters G_v, B_v, D_v, H_v, and q_v have been determined for all newly detected bands. The line intensities of 13 weak bands have been measured. The uncertainty of the obtained line intensity values varies from 7 to 13%.     

The Effect of Zinc Oxide and Calcium Carbonate Nanoparticles on the Thermal Conductivity of Polypropylene

The thermal conductivity (TC) of compression-moulded polypropylene (PP) and PP filled with 5–15% zinc oxide (ZnO) or calcium carbonate (CaCO₃) nanoparticles, prepared by extrusion, was studied using a thermal conductivity analyzer (TCA). The effect of nanoparticle content and crystallinity on the thermal conductivity was investigated using conventional methods, including SEM, XRD, and DSC. The incorporation of nanoparticles improved the crystallinity and thermal conductivity simultaneously. The experimental TC values of the PP nanocomposites with different level of nanoparticles concentration showed a linear increase with an increase in crystallinity. The TC improvement in PP/ZnO nanocomposite was greater than that of PP/calcium carbonate nanocomposites. This fact can be attributed to the intrinsic, better thermal conductivity of the ZnO nanoparticles. Several models were used for prediction of the TC in the nanocomposites. In the PP/ZnO nanocomposites the TC values correlated well with the values predicted by the Series, Maxwell, Lewis and Nielson, Bruggeman, and De Loor models up to 10 wt%.     

Quantification of the Particle Size and Stability of Graphene Oxide in a Variety of Solvents

The exceptional solution processing potential of graphene oxide (GO) is always one of its main advantages over graphene in terms of its industrial relevance in coatings, electronics, and energy storage. However, the presence of a variety of functional groups on the basal plane and edges of GO makes understanding suspension behavior in aqueous and organic solvents, a major challenge. Acoustic spectroscopy can also measure zeta potential to provide unique insight into flocculating, meta‐stable, and stable suspensions of GO in deionized water and a variety of organic solvents (including ethanol, ethylene glycol, and mineral oil). As expected, a match between solvent polarity and the polar functional groups on the GO surface favors stable colloidal suspensions accompanied by a smaller aggregate size tending toward disperse individual flakes of GO. This work is significant since it describes the characteristics of GO in solution and its ability to act as a precursor for graphene‐based materials.