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.     

Raman spectra of complexes of HNO3 and NO3- with NO2 at surfaces and with N2O4 in solution

Raman spectra of HNO(3).NO(2) have been detected on liquid and solid surfaces in the presence of concentrated HNO(3) and NO(2) gas. The Raman spectrum of HNO(3) solutions containing N(2)O(4) has been partly reinterpreted in terms of contributions from HNO(3).N(2)O(4) and N(2)O(4).NO(3)(-) complexes.     

Simultaneous determination of δ15N and δ18O of N2O and δ13C of CH4 in nanomolar quantities from a single water sample

We have developed a rapid, sensitive, and automated analytical system to simultaneously determine the concentrations and stable isotopic compositions (δ¹⁵N, δ¹⁸O, and δ¹³C) of nanomolar quantities of nitrous oxide (N₂O) and methane (CH₄) in water, by combining continuous‐flow isotope‐ratio mass spectrometry and a helium‐sparging system to extract and purify the dissolved gases. Our system, which is composed of cold traps and a capillary gas chromatograph that use ultra‐pure helium as the carrier gas, achieves complete extraction of N₂O and CH₄ in a water sample and separation among N₂O, CH₄, and the other component gases. The flow path following exit from the gas chromatograph was periodically changed to pass the gases through the combustion furnace to convert CH₄ and the other hydrocarbons into CO₂, or to bypass the combustion furnace for the direct introduction of eluted N₂O into the mass spectrometer, for determining the stable isotopic compositions through monitoring the ions of m/z 44, 45, and 46 of CO and N₂O⁺. The analytical system can be operated automatically with sequential software programmed on a personal computer. Analytical precisions better than 0.2‰ and 0.3‰ and better than 1.4‰ and 2.6‰ were obtained for the δ¹⁵N and δ¹⁸O of N₂O, respectively, when more than 6.7 nmol and 0.2 nmol of N₂O, respectively, were injected. Simultaneously, analytical precisions better than 0.07‰ and 2.1‰ were obtained for the δ¹³C of CH₄ when more than 5.5 nmol and 0.02 nmol of CH₄, respectively, were injected. In this manner, we can simultaneously determine stable isotopic compositions of a 120 mL water sample with concentrations as low as 1.7 nmol/kg for N₂O and 0.2 nmol/kg for CH₄. Copyright © 2010 John Wiley & Sons, Ltd.     

Infrared evidence of NO linkage photoisomerization in Na2[Fe(CN)5NO].2H2O at low temperature: experimental and theoretical (DFT) isotopic shifts from 15n(O), 18O and 54Fe species

Infrared spectra of the metastable state I (MSI) of normal and 15NO, N18O and 54Fe isotopically substituted sodium nitroprusside dihydrate (Na2[Fe(CN)5NO].2H2O) have been obtained at 77 K. A comparison of the isotopic shifts measured for the vibrational modes of the FeXY (XY = NO or ON) moiety with those calculated by means of quantum chemistry (DFT) procedures supports the linear Fe-O = N arrangement for the MSI state.     

Photocurrent kinetics at the electron emission from a metal into electrolyte solution: Part II. Solutions without acceptors and solutions of N2O,NO2−, NO3−

A method of measuring the kinetics of currents arising at the electron photoemission from a metal into electrolyte solution when affected by the u.v. laser pulses for 10^?8 s at the frequency of repetitions 10–25 Hz is described. Measurements have been taken in solutions without acceptors and in those containing N₂O and NO₂^?, NO₃^? ions as electron acceptors. The rate constants of capture of the solvated electrons by N₂O ((6±1)×0⁹ mol^?1 s^?1) and NO₂^? ((4.5±1)×10⁹ mol^?1 s^?1) and the diffusion coefficients of OH-radicals ((1.0±0.3)×10^?5 cm² s^?1) and of NO ((1.2±0.3)×10^?5 cm² s^?1) are found. The oxidation rate of NO₃^2? has been shown to decrease from 40 cm s^?1 in the range of potentials ?0.55 to ?1.0 V. The rate constant of bimolecular recombination of the solvated electrons ((1.3±0.4)×10¹⁰ mol^?1 s^?1) has been found from the dependence of the emitted charge on the light intensity.     

A study of the reaction of N+ with O2: experimental quantification of NO+(a 3Sigma+) production (298-500 K) and computational study of the overall reaction pathways

The product branching ratios for NO+(X 1Sigma+) and NO+(a 3Sigma+) produced from the reaction of N+ with O2 have been measured at 298 and 500 K in a selected ion flow tube. Approximately 0.5% of the total products are in NO+(a) at both temperatures, despite the fact that the reaction to form NO+(a) is 0.3 eV exothermic. High-level ab initio calculations of the potential energy surfaces for the N+ + O2 reaction show that the reaction from N+(3P) + O2(3Sigma(g)) reactants starts with an efficient early stage charge transfer to the N(2D) + O2+(X 2Pi) channel, which gives rise to the O2+(X 2Pi) product and, at the same time, serves as the starting point for all of the reaction channels leading to NO+ and O+ products. Pathways to produce NO+(a 3Sigma+) are found to be less favorable than pathways leading to the major product NO+(X 1Sigma+). Production of N(2D) has implications for the concentration of NO in the mesosphere.