CO LMR spectrum of14N16O and its analysis with spectra of14N17O and14N18O

LMR spectra for v=1←0 transitions of¹⁴N¹⁶O in X²II_{1/2, 3/2} states were observed at 5.6 μm and 5.4 μm of CO laser. Introducing the advanced isotopic molecular constant scaling function to Hund’s case (a) diatomic structure model, these spectra were analyzed and fitted together with all reliable previous spectral data of¹⁴N¹⁶O as well as¹⁴N¹⁷O and¹⁴N¹⁸O. A full set of precise molecular parameters and their vibrational dependencies have been determined with much higher precision (1–2 orders for most parameters). Many of them have been obtained for the first time. Using isotopic scaling function, the molecular constants of¹⁴N¹⁷O and¹⁴N¹⁸O were deduced.     

CO LMR spectrum of14N16O and its analysis with spectra of14N17O and14N18O

LMR spectra for v=1←0 transitions of¹⁴N¹⁶O in X²II_{1/2, 3/2} states were observed at 5.6 μm and 5.4 μm of CO laser. Introducing the advanced isotopic molecular constant scaling function to Hund’s case (a) diatomic structure model, these spectra were analyzed and fitted together with all reliable previous spectral data of¹⁴N¹⁶O as well as¹⁴N¹⁷O and¹⁴N¹⁸O. A full set of precise molecular parameters and their vibrational dependencies have been determined with much higher precision (1–2 orders for most parameters). Many of them have been obtained for the first time. Using isotopic scaling function, the molecular constants of¹⁴N¹⁷O and¹⁴N¹⁸O were deduced.     

Potential energy surfaces and vibrational spectra for isotopomers of N_2O

ＴｈｅＮ2Ｏｍｏｌｅｃｕｌｅｐｌａｙｓａｖｅｒｙｉｍｐｏｒｔａｎｔｒｏｌｅｉｎｏｚｏｎｅｃｈｅｍｉｓｔｒｙｉｎｔｈｅａｔｏｍｏｓｐｈｅｒｅ.Ｉｔｓｒｏｖｉｂｒａｔｉｏｎａｌｓｐｅｃｔｒａｃａｎｐｒｏｖｉｄｅｕｓｅｆｕｌｉｎｆｏｒｍａｔｉｏｎａｂｏｕｔｔｈｅｉｎｔｒａｍｏｌｅｃｕｌａｒｄｙｎａｍｉｃｐｒｏｐｅｒｔｉｅｓ.Ｎ2Ｏｉｓａｌｉｎｅａｒｍｏｌｅｃｕｌｅａｔｔｈｅｅｑｕｉｌｉｂｒｉｕｍｇｅｏｍｅｔｒｙｆｏｒｔｈｅｅｌｅｃｔｒｏｎｉｃｇｒｏｕｎｄｓｔａｔｅ.Ｎｕｍｅｒｏｕｓｉｎｖｅｓｔｉｇａｔｉｏ…     

Infrared spectra of helium clusters seeded with nitrous oxide, 4HeN-N2O, with N=1-80

High resolution infrared spectra of HeN-N2O clusters are studied in the 2200 cm(-1) region of the N2O nu1 fundamental band. The clusters are produced in a pulsed supersonic jet expansion from a cooled nozzle source and probed using a tunable diode laser operating in a rapid-scan mode. Three isotopic forms are used (14N14N16O, 15N14N16O, and 15N15N16O) in order to support the spectral analyses. For clusters up to N approximately 24, the individual spectra are resolved, assigned, and analyzed together with complementary microwave data. Assignments for larger clusters are uncertain due to overlapping transitions, but an approximate analysis is still possible for N approximately 25-80. Compared to helium clusters containing the related CO2 or OCS molecules, the rotational dynamics of HeN-N2O clusters show similarities but also important differences. In particular, HeN-N2O has more irregular behavior in the range of N=6-17, indicating that conventional molecular structure plays a greater role. In general terms, these differences can be attributed to a greater degree of angular anisotropy in the He-N2O intermolecular potential.     

14N NQR study of nicotinamide and related compounds

14N nuclear quadrupole resonance (NQR) frequencies have been measured in picolinamide, nicotinamide, isonicotinamide, 2,6-pyridine dicarboxamide, and acetamide by double resonance. The 14N NQR spectra in picolinamide, nicotinamide, isonicotinamide, and 2,6-pyridine dicarboxamide show the presence of two distinct nitrogen positions: the ring position with the quadrupole coupling constant about 4,5 MHz and the amide position with the quadrupole coupling constant about 2.6 MHz. The NQR data are related to the structure of the investigated compounds and to the N--H...O hydrogen bonds.     

NMR Spectra of Cyclic Nitrones. 7. The Influence of Substituents and a Hydrogen Bond on <Superscript>14</Superscript>N and <Superscript>17</Superscript>O Chemical Shifts in Derivatives of 3-Imidoazoline 3-Oxide

Derivatives of 3-imidazoline 3-oxide have been studied by ¹⁴N and ¹⁷O NMR methods. Regularities of the influence of substituents and of a hydrogen bond on chemical shifts have been made apparent. The range of changes of the chemical shifts of the nitrogen and oxygen nuclei of the nitrone group has been determined. Both in the ¹⁷O and in the ¹⁴N NMR spectra the signals of the amino derivatives are the highest field signals for the nitrone group, and the lowest field signals are the signals of the cyano derivatives in the series of derivatives investigated. Depending on the substituent (from amino to cyano group) the ¹⁷O chemical shifts varied over a range ∼155 ppm, but the interval of change of the ¹⁴N chemical shifts for the same substituents was ∼110 ppm. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1336–1341. September, 2005.     

含穴醚N8O3配体的金属大环化合物的NMR研究

在溶液中,室温下对含有穴醚Ｎ８Ｏ３配体（Ｈ３Ｌ）的金属大环化合物［Ｎａ（Ｈ３Ｌ）］（ＣｌＯ４）３Ｈ２Ｏ（２）和［Ｌａ（Ｈ３Ｌ）（ＯＨ）２］（ＣｌＯ４）３（３）,作了１ＨＮＭＲ谱的测定,在化合物（２）－乙腈溶液中加入过量Ｌａ（ＣｌＯ４）３后的（２＋Ｌａ）和化合物（３）还作了１３Ｃ和１Ｈ－１ＨＣＯＳＹ（氢－氢相关二维谱）、１Ｈ－１３ＣＨＭＱＣ（氢核检测的异核多量子相干相关谱）及１Ｈ－１３ＣＨＭＢＣ（氢核检测的异核多键相关谱）的ＮＭＲ谱测定,归属了所有１Ｈ,１３Ｃ的谱线。对其配位行为通过１ＨＮＭＲ试验作了简单的讨论。     

Using dual-bacterial denitrification to improve delta15N determinations of nitrates containing mass-independent 17O

The bacterial denitrification method for isotopic analysis of nitrate using N(2)O generated from Pseudomonas aureofaciens may overestimate delta(15)N values by as much as 1-2 per thousand for samples containing atmospheric nitrate because of mass-independent (17)O variations in such samples. By analyzing such samples for delta(15)N and delta(18)O using the denitrifier Pseudomonas chlororaphis, one obtains nearly correct delta(15)N values because oxygen in N(2)O generated by P. chlororaphis is primarily derived from H(2)O. The difference between the apparent delta(15)N value determined with P. aureofaciens and that determined with P. chlororaphis, assuming mass-dependent oxygen isotopic fractionation, reflects the amount of mass-independent (17)O in a nitrate sample. By interspersing nitrate isotopic reference materials having substantially different delta(18)O values with samples, one can normalize oxygen isotope ratios and determine the fractions of oxygen in N(2)O derived from the nitrate and from water with each denitrifier. This information can be used to improve delta(15)N values of nitrates having excess (17)O. The same analyses also yield estimates of the magnitude of (17)O excess in the nitrate (expressed as Delta(17)O) that may be useful in some environmental studies. The 1-sigma uncertainties of delta(15)N, delta(18)O and Delta(17)O measurements are +/-0.2, +/-0.3 and +/-5 per thousand, respectively.     

Potential energy surfaces and vibrational spectra for isotopomers of N2O

Potential energy surfaces and vibrational spectra for the four isotopomers (^l5N¹⁴N¹⁶O,^l4N^I5N¹⁶O,¹⁵N₂ ¹⁶O and¹⁵N₂ ¹⁸O) of N₂O have been investigated with the vibrational self-consistent field-configuration interaction method. It is shown that the isotopomers with the same end atom have similar values of the potential parameters, and that substitution with different end atoms can affect the potential obviously. The calculated vibrational levels are in good agreement with the observed values by the optimization of several potential parameters (f ₁ ⁽¹⁾,f ₁₃ ⁽⁰⁾,f ₃ ⁽¹⁾ which are sensitive to isotopic substitutions. Project supported by the National Natural Science Foundation of China (Grant No. 29673029).     

Partial pressure dependency of 17O/16O and 18O/16O of molecular oxygen in the mass spectrometer

A method to determine both (17)O/(16)O and (18)O/(16)O ratios for molecular oxygen with high precision by direct introduction into the mass spectrometer without gas separation is presented. Because both (17)O/(16)O and (18)O/(16)O in mixed gases have good linear correlations with their mixing ratios, these isotopic compositions can be determined without a gas-separation procedure by calibration using prepared standard gases with variable mixed ratios and by monitoring the amounts of fragment ions. Analytical precision for delta(17)O and delta(18)O of 45 and 7 per meg, respectively, were obtained. The observed partial pressure dependency of isotopic composition may be caused by isotope fractionation during admission from the ionization chamber into the flight tube of the mass spectrometer.     

H_2O_2氧化N_2生成N_2O和H_2O机理的研究

采用量子化学计算方法研究了Ｈ２Ｏ２ 氧化Ｎ２ 生成Ｎ２Ｏ 和Ｈ２Ｏ 的机理．结果发现, Ｈ２Ｏ２ 氧化Ｎ２ 先通过１ 个四元环过渡态形成中间体Ｈ２Ｎ２Ｏ２ 分子,Ｈ２Ｎ２Ｏ２ 再通过一个五元环过渡态形成Ｎ２Ｏ和Ｈ２Ｏ．根据计算得到的每步反应的活化能,得知Ｈ２Ｏ２ 氧化Ｎ２ 生成中间体Ｈ２Ｎ２Ｏ２ 分子是整个反应的控制步骤．     

17O and 14N spectroscopy of 17O-labeled nucleic acid bases

Oxygen-17 and nitrogen-14 nuclear magnetic resonance techniques have been utilized in studying liquid-state hydrogen bonding interactions between nucleic acid bases and between the bases and solvent. The bases uracil and thymine have been labeled with ¹⁷O at positions 2 and 4, cytosine at position 2 and thymine riboside at position 4. The ¹⁷O chemical shift was found to be a sensitive structural probe and to provide information concerning the resonance forms that contribute to the total wave function. The chemical shift of the oxygen of thymine and uracil at position 2 was detected at a higher field than that of oxygen at position 4, presumably owing to an increased contribution of single bonded-oxygen valence bond structures at position 2. The ¹⁷O and ¹⁴N chemical shifts of cytosine were found to be strongly pH dependent, and the results have been interpreted in terms of predominant cytosine resonance structures contributing to the aqueous cation and anion. The ¹⁷O line width of cytosine in aqueous solution indicates the presence of hydrogen bonded dimers between neutral and cationic forms.     

Yields and average cross sections of recoil charged particle induced reactions on11B,12C,13C,14N,16O and18O

The yield and average cross section for the reactions¹¹B(p, n)¹¹C,¹²C(p, )¹³N,¹³C(p, n)¹³N, ₁₂ ¹² C(d, n)¹³N,¹⁴N(p, )¹¹C,¹⁶O(p, )¹³N,¹⁶O(d, n)¹⁷F,¹⁶O(t, n)¹⁸F, and¹⁸O(p, n)¹⁸F have been measured in different compounds. The charged particles were created in the samples themselves either through recoil by scattering of 14 MeV neutrons off hydrogen and deuterium, or by the (n, t) reaction on⁶Li using thermal neutrons. The yields of reactions¹²C(d, n);¹⁶O(p, );¹⁶O(t, n) and¹⁸O(p, n) have been measured using proton, deuteron and triton spectra generated by 14 MeV neutrons in the reactions D(n, p)2n;⁶Li(n, d);⁷Li(n, d) and¹⁰B(n, d);⁷Li(n, t) and¹⁰B(n, t), respectively.     

Vertical gradients of delta15N and delta18O in soil atmospheric N2O--temporal dynamics in a sandy soil

The greenhouse gas nitrous oxide (N(2)O) can be both formed and consumed by microbial processes in the soil. As these processes fractionate strongly in favour of (14)N and (16)O, delta(15)N and delta(18)O gradients of N(2)O in the soil profile may elucidate patterns of N(2)O formation, consumption or emission to the atmosphere. We present the first in situ data of such gradients over time for a mesic typic Haplaquod seeded with potatoes (Solanum tuberosum L.). On two adjacent fields in 2002 and 2003, topsoil N(2)O fluxes were measured and the soil atmosphere was regularly sampled for N(2)O concentrations, delta(15)N and delta(18)O signatures of N(2)O at depths of 18, 48 and 90 cm during approximately 400 days. During the entire sampling period, the N(2)O concentrations were the highest and the delta(15)N signatures the lowest in the subsoil (48 or 90 cm depth) as compared with the topsoil, indicating production of N(2)O in the subsoil. For delta(15)N, differences greater than 30 per thousand between topsoil and subsoil on the same date were regularly observed. The highest N(2)O concentration of 100385 microL m(-3) at 90 cm depth on 1 July 2003, was preceded by the lowest delta(15)N value of -43.5 per thousand one week earlier. This was followed by a 150-day general decrease of N(2)O concentrations at 90 cm depth to 1723 microL m(-3) and a simultaneous enrichment of delta(15)N to +7.1 per thousand, mostly without a significant topsoil flux. There was a negative logarithmic relationship between N(2)O concentration at 90 cm depth and its delta(15)N signature. This relationship indicated a delta(15)N signature of -40 to -45 per thousand during the production of N(2)O in the subsoil, and a subsequent enrichment during the consumption of N(2)O. We conclude that the isotopic signature of the N(2)O topsoil flux is the result of various processes of consumption and production at different depths in the soil profile. It is therefore not a reliable estimator for the overall delta(15)N signature of N(2)O in the soil atmosphere, nor for indirect losses of N(2)O to the environment. Therefore, these findings will pose a further challenge to ongoing efforts to draw up a global isotopic budget for N(2)O.     

Determination of the 15N/14N, 17O/16O, and 18O/16O ratios of nitrous oxide by using continuous-flow isotope-ratio mass spectrometry

We developed a rapid, sensitive, and automated analytical system to determine the delta15N, delta18O, and Delta17O values of nitrous oxide (N2O) simultaneously in nanomolar quantities for a single batch of samples by continuous-flow isotope-ratio mass spectrometry (CF-IRMS) without any cumbersome and time-consuming pretreatments. The analytical system consisted of a vacuum line to extract and purify N2O, a gas chromatograph for further purification of N2O, an optional thermal furnace to decompose N2O to O2, and a CF-IRMS system. We also used pneumatic valves and pneumatic actuators in the system so that we could operate it automatically with timing software on a personal computer. The analytical precision was better than 0.12 per thousand for delta15N with >4 nmol N2O injections, 0.25 per thousand for delta18O with >4 nmol N2O injections, and 0.20 per thousand for Delta17O with >20 nmol N2O injections for a single measurement. We were also easily able to improve the precision (standard errors) to better than 0.05 per thousand for delta15N, 0.10 per thousand for delta18O, and 0.10 per thousand for Delta17O through multiple analyses with more than four repetitions with 190 nmol samples using the automated analytical system. Using the system, the delta15N, delta18O, and Delta17O values of N2O can be quantified not only for atmospheric samples, but also for other gas or liquid samples with low N2O content, such as soil gas or natural water. Here, we showed the first ever Delta17O measurements of soil N2O.     

The missing link: triplet fluorocarbonyl nitrene FC(O)N

The elusive triplet fluorocarbonyl nitrene, FC(O)N (X³A′′), has been generated in high yield from matrix‐isolated FC(O)N₃ by ArF excimer laser photolysis (λ=193 nm). As a side product FNCO was formed. The novel nitrene was characterized by IR, UV/Vis, EPR spectroscopy, and quantum‐chemical calculations. All six fundamental vibrations of FC(O)N at 1681.3, 1193.8, 879.8, 646.5, 588.7, and 434.8 cm^?1 (argon matrix, 16 K), their ^12/13C, ^16/18O, and ^14/15N isotopic shifts, and four electronic transitions at T₀=13 890, 25 428, 29 166, and 30 900 cm^?1 that exhibit vibrational fine structures have been detected. Under visible‐light irradiation at λ≥495 nm, FC(O)N reacted with molecular N₂ in the matrix cage at 6 K to give back FC(O)N₃, whereas near‐UV irradiation at λ≥335 nm yielded FNCO. The singlet–triplet energy gaps of different carbonyl nitrenes are discussed.     

Isotope fractionation factors of N2O diffusion

Isotopic signatures of N2O are increasingly used to constrain the total global flux and the relative contribution of nitrification and denitrification to N2O emissions. Interpretation of isotopic signatures of soil-emitted N2O can be complicated by the isotopic effects of gas diffusion. The aim of our study was to measure the isotopic fractionation factors of diffusion for the isotopologues of N2O and to estimate the potential effect of diffusive fractionation during N2O fluxes from soils using simple simulations. Diffusion experiments were conducted to monitor isotopic signatures of N2O in reservoirs that lost N2O by defined diffusive fluxes. Two different mathematical approaches were used to derive diffusive isotope fractionation factors for 18O (epsilon18O), average 15N (epsilonbulk) and 15N of the central (alpha(-)) and peripheral (beta(-)) position within the linear N2O molecule (epsilon15Nalpha, epsilon15Nbeta). The measured epsilon18O was -7.79 +/- 0.27 per thousand and thus higher than the theoretical value of -8.7 per thousand. Conversely, the measured epsilonbulk (-5.23 +/- 0.27 per thousand) was lower than the theoretical value (-4.4 per thousand). The measured site-specific 15N fractionation factors were not equal, giving a difference between epsilon15Nalpha and epsilon15Nbeta (epsilonSP) of 1.55 +/- 0.28 per thousand. Diffusive fluxes of the N2O isotopologues from the soil pore space to the atmosphere were simulated, showing that isotopic signatures of N2O source pools and emitted N2O can be substantially different during periods of non-steady state fluxes. Our results show that diffusive isotope fractionation should be taken into account when interpreting natural abundance isotopic signatures of N2O fluxes from soils.     

Influence of flooding on delta15N, delta18O, 1delta15N and 2delta15N signatures of N2O released from estuarine soils--a laboratory experiment using tidal flooding chambers

The influence of flooding on N2O fluxes, denitrification rates, dual isotope (delta18O and delta15N) and isotopomer (1delta15N and 2delta15N) ratios of emitted N2O from estuarine intertidal zones was examined in a laboratory study using tidal flooding incubation chambers. Five replicate soil cores were collected from two differently managed intertidal zones in the estuary of the River Torridge (North Devon, UK): (1) a natural salt marsh fringing the estuary, and 2 a managed retreat site, previous agricultural land to which flooding was restored in summer 2001. Gas samples from the incubated soil cores were collected from the tidal chamber headspaces over a range of flooding conditions, and analysed for the delta18O, delta15N, 1delta15N and 2delta15N values of the emitted N2O. Isotope signals did not differ between the two sites, and nitrate addition to the flooding water did not change the isotopic content of emitted N2O. Under non-flooded conditions, the isotopic composition of the emitted N2O displayed a moderate variability in delta18O and 2delta15N delta values that was expected for microbial activity associated with denitrification. However, under flooded conditions, half of the samples showed strong and simultaneous depletions in 1delta15N and delta18O values, but not in 2delta15N. Such an isotope signal has not been reported in the literature, and it could point towards an unidentified N2O production pathway. Its signature differed from denitrification, which was generally the N2O production pathway in the salt marsh and the managed retreat site.     

Sr14-xCaxCu24O41的芯能级光电子发射谱

The core-level X-ray photoelectron emission spectra of the quasi-one dimensional spin 1/2 antiferromagnetic system Sr14-xCaxCu24O41(x=0, 3.5, 6, 7, 8.4) were measured. The main peak of Cu2p3/2 was about 933.8 eV, and the full width of half maximum height was about 3.3 eV. Simulation of Cu2p3/2 by XPSPEAK41 shows that the percents of Cu2+ and Cu3+ in Sr14Cu24O41 are 92.13% and 7.87%, no obvious change to Cu2p core-level is observed by the partial substituting Ca for Sr, and the average valence of Cu in this system is estimated to be 2.08. The main peak of O1s is about 531.0 eV, and the weak shoulder toward the low binding energy direction can be considered as the contribution of Ca-O bond. The binding energies of Ca2p3/2 and Sr3d5/2 indicate that their valence in this system are both +2, without mixed valence.     

Comparison of rovibronic density of asymmetric versus symmetric NO2 isotopologues at dissociation threshold: broken symmetry effects

We have measured the rovibronic densities of four symmetric (C2v) and two asymmetric (Cs) isotopologues of nitrogen dioxide just below their photodissociation threshold. At dissociation threshold and under jet conditions the laser-induced fluorescence abruptly disappears because the dissociation into NO(2pi(1/2)) + O(3P2) is much faster than the radiative decay. As a consequence, in a narrow energy range below D0, the highest bound rovibronic energy levels of J=1/2 and J=3/2 can be observed and sorted. A statistical analysis of the corresponding rovibronic density, energy spacing, and rovibronic transition intensities has been made. The observed intensity distributions are in agreement with the Porter-Thomas distribution. This distribution allows one to estimate the number of missing levels, and therefore to determine and compare the rovibronic and the vibronic densities. The four symmetric NO2 isotopologues, 16O14N16O, 18O14N18O, 16O15N16O, and 18O15N18O, have, respectively, a sum of J=1/2 and J=3/2 rovibronic densities of 18+/-0.8, 18.3+/-1.4, 18.4+/-2.7, and 19.8+/-3.5 cm(-1), while for the two asymmetric isotopologues, 18O14N16O and 18O15N16O, the corresponding densities are 20.9+/-4.5 and 23.6+/-5.6 cm(-1). The corresponding vibronic densities are in agreement only if we include both the merging of symmetry species (from those of C2v to those of Cs) and the contribution of the long-range tail(s) of the potential-energy surface along the dissociation coordinate. The effects of isotopic substitution on dissociation rates and the possible relation to mass-independent isotopic fractionation are discussed.