Bond-forming reactions of N22+ with C2H4, C2H6, C3H4 and C3H6

Mass spectrometry, coupled with position-sensitive coincidence detection, has been used to investigate the reactions of N22+ with various small hydrocarbon molecules (C2H4, C2H6, C3H4, c-C3H6 and n-C3H6) at collision energies below 10 eV in the centre-of-mass frame. The reactivity, in each case, is dominated by electron transfer. However, in each collision system we also clearly identify products formed following the creation of new chemical bonds. These bond-forming reactions comprise two distinct classes: (i) hydride transfer reactions which initially form NnH+ (n = 1, 2) and (ii) N+ transfer reactions which form monocationic products with Csingle bondN bonds. These bond-forming reactions make a small (5–10%), but significant, contribution to the overall product ion yield in each collision system. The temporal and positional data recorded by our coincidence detection technique are used to construct scattering diagrams which reveal the mechanisms of the bond-forming reactions. For the hydride transfer process, the scattering diagrams reveal that H− is directly transferred from the hydrocarbon to N22+ at significant interspecies separations. For the hydride transfer reactions with C2H4, C2H6 and C3H4, we observe fragmentation of the nascent N2H+* to form NH+ + N. The N+ transfer reaction also proceeds by a direct mechanism: a single step involving N+/H exchange results in the formation of a singly-charged organic species containing a Csingle bondN bond which is detected in coincidence with H+. The two general classes of bond-forming reactivity we observe in the reactions of N22+ with organic molecules may be relevant in the chemistry of energised environments rich in molecular nitrogen and hydrocarbon species, such as the atmosphere of Titan

Improved mixing height monitoring through a combination of lidar and radon measurements

Surface-based radon (222Rn) measurements can be combined with lidar backscatter to obtain a higher quality time series of mixing height within the planetary boundary layer (PBL) than is possible from lidar alone, and a more quantitative measure of mixing height than is possible from only radon. The reason why lidar measurements are improved is that there are times when lidar signals are ambiguous, and reliably attributing the mixing height to the correct aerosol layer presents a challenge. By combining lidar with a mixing length scale derived from a time series of radon concentration, automated and robust attribution is possible during the morning transition. Radon measurements provide mixing information during the night, but concentrations also depend on the strength of surface emissions. After processing radon in combination with lidar, we obtain nightly measurements of radon emissions and are able to normalise the mixing length scale for changing emissions. After calibration with lidar, the radonderived equivalent mixing height agrees with other measures of mixing on daily and hourly timescales and is a potential method for studying intermittent mixing in nocturnal boundary layers.© 2013, Copernicus Publications

Bond-forming reactions between the molecular oxygen dication and small organic molecules

The reactions of O22+ with CH4, C2H2 and C2H4 have been investigated for the first time, using a position-sensitive coincidence technique, at centre-of-mass collision energies close to 4 eV. The experiments show these interactions yield a wide variety of products which involve the formation of new chemical bonds. The mechanisms of these bond-forming reactions have been investigated by examining the correlations between the velocities of the reactant and product ions which are revealed by the coincidence data. Many of the bond-forming reactions occur via the stripping of an atom (or group of atoms) from the neutral by the O22+ reactant, while other reactions clearly involve the initial formation of a collision complex which then fragments to form the detected products

Electron transfer and bond-forming reactions following collisions of I2+ with CO and CS2

Collisions between I2+ and CO have been investigated using time-of flight mass spectrometry at a range of centre-of-mass collision energies between 0.5 eV and 3.0 eV. Following I2+ + CO collisions we detect I+ + CO+ from a single-electron transfer reaction and IO+ + C+ from bond-forming reactivity. Reaction-window calculations, based on Landau-Zener theory, have been used to rationalise the electron transfer reactivity and computational chemistry has been used to explore the [I-CO] 2+ potential energy surface to account for the observation of IO+. In addition, collisions between I2+ and CS2 have been investigated over a range of centre-of-mass collision energies between 0.8 eV and 6.0 eV. Both single and double electron transfer reactions are observed in the I2+/CS2 collision system, an observation again rationalized by reaction-window theory. The monocations IS+ and IC+ are also detected following collisions of I2+ with CS2, and these ions are clearly products from a bond-forming reaction. We present a simple model based on the structure of the [I-CS2]2+ collision complex to rationalize the significantly larger yield of IS+ than IC+ in this bond-forming process

A comparison between direct and pan-derived measurements of the isotopic composition of atmospheric waters

The stable isotopes of water can be used to examine and quantify the contribution to atmospheric moisture from evaporation, transpiration and surface-waters. However, obtaining extensive and ongoing time series data of the isotopic composition of atmospheric moisture has been difficult. Presented here is an alternate method using an isotope mass balance approach to estimate the isotopic composition of atmospheric moisture using water samples collected from class A evaporation pans. While this evaporation pan method does not provide the high-resolution time series data that can be obtained from an isotope analyser taking in-situ measurements of atmospheric moisture, the method is relatively simple and inexpensive to set-up and maintain. In this preliminary investigation, a comparison between the isotopic composition of atmospheric moisture estimated from the evaporation pan method and in-situ measurements of the isotopic composition of water vapour using a Fourier Transform Infrared (FTIR) spectrometer deployed at the Lucas Heights weather station in New South Wales is undertaken. Through comparison of the two series of hydrogen isotope data, an assessment of the evaporation pan method can be made. Although there was some agreement between the isotopic composition of vapour measured by the FTIR spectrometer and the estimation for the atmospheric moisture (R2 = 0.49), the comparison is sensitive to climatic parameters that vary significantly within a 24-hour period such as the relative humidity of air and the air and pan temperatures. Inverting the model to use the FTIR spectrometer measurements at an hourly resolution improved the performance of the model (R2 =0.57). However, this also revealed that the model produced more depleted values of the evaporation pan water isotopes than those observed. In contrast, there was a variable relationship between the modelled and observed isotope values of atmospheric moisture. These conflicting results will need to be resolved before the evaporation pan method is broadly applied in isotope hydrology. © 2011 The Modelling and Simulation Society of Australia and New Zealand Inc

In-situ measurements of the stable isotopic composition of atmospheric water vapour using FTIR spectroscopy.

The stable isotopic composition of atmospheric water vapour is related to the hydrological processes that occur along the back trajectory of an air mass, including evaporation at the moisture source, atmospheric mixing and precipitation. Thus, by collecting continuous measurements of the stable isotopes in water vapour a record of the hydrological history of air passing a site can be compiled. To collect such a record a FTIR instrument capable of making real‐time in‐situ measurements of the stable isotopes in water vapour has been developed. The instrument has been deployed at a site near Sydney, Australia for approximately 18 months. During this time we have shown that the FTIR instrument compares well with laser based analysers that are capable of making similar real‐time measurements. In addition to the comparison between the different analysers, we have been investigating some of the large signals that are observed in the time series of isotopic measurements. The analysis of the dataset indicates that the lowest isotope values are generally associated with cold fronts that pass over the South East of the Australian Continent and then over the Sydney region. When a cold front passes over or near the measurement site, the deuterium isotope value can be observed to change by up to 100 per mille within the space of a few hours. In addition, cold frontal passages with contrasting moisture source and precipitation histories exhibit systematic differences in water vapour stable isotope signals as they pass over Sydney. On the other hand, higher and more slowly changing isotope values are generally associated with anticyclonic conditions. The study shows that for our site the variations in the stable isotope values are strongly influenced by the hydrological history of air parcels at a synoptic scale.COST action ES0604; Institut Pierre-Simon Laplac

Bimolecular reactions of the dications and trications of atoms and small molecules in the gas-phase

This review discusses the recent developments in our understanding of the electron transfer and bond-forming reactions of small atomic and molecular dications in the gas-phase. A summary of the properties of isolated dications is presented, followed by a review of the major experimental techniques used to probe dicationic reactivity. Electron transfer reactions of dications with neutral species are then discussed, including recent rationalizations of this class of reactivity using simple electrostatic models. Our current understanding of the reactions of dications with neutral atoms and molecules which result in the formation of new chemical bonds is then presented. This part of the account is built around three case studies, including some new results on the bond-forming reactions of O2^2+ with CH4. Moving beyond dicationic species, the account then discusses recent results concerning the bond-forming reactivity of tricationic atoms and small molecules. This section includes the mechanistic conclusions drawn from the first results involving the coincident detection of all three positively charged species generated from the reaction of a molecular trication: CS2 3+ + O2 → SO+ + CS+ + O+. The review concludes with some thoughts concerning the future development of the field

Functional Locomotor Consequences of Uneven Forefeet for Trot Symmetry in Individual Riding Horses

ABSTRACT: Left-right symmetrical distal limb conformation can be an important prerequisite for a successful performance, and it is often hypothesized that asymmetric or uneven feet are important enhancing factors for the development of lameness. On a population level, it has been demonstrated that uneven footed horses are retiring earlier from elite level competition, but the biomechanical consequences are not yet known. The objectives of this study were to compare the functional locomotor asymmetries of horses with uneven to those with even feet. Hoof kinetics and distal limb kinematics were collected from horses (n = 34) at trot. Dorsal hoof wall angle was used to classify horses as even or uneven (1.5° difference between forefeet respectively) and individual feet as flat (55°). Functional kinetic parameters were compared between even and uneven forefeet using MANOVA followed by ANOVA. The relative influences of differences in hoof angle between the forefeet and of absolute hoof angle on functional parameters were analysed using multiple regression analysis (P<0.05). In horses with uneven feet, the side with the flatter foot showed a significantly larger maximal horizontal braking and vertical ground reaction force, a larger vertical fetlock displacement and a suppler fetlock spring. The foot with a steeper hoof angle was linearly correlated with an earlier braking-propulsion transition. The conformational differences between both forefeet were more important for loading characteristics than the individual foot conformation of each individual horse. The differences in vertical force and braking force between uneven forefeet could imply either an asymmetrical loading pattern without a pathological component or a subclinical lameness as a result of a pathological development in the steeper foot

Movement asymmetries in horses presented for prepurchase or lameness examination

Background The increasing popularity of objective gait analysis makes application in prepurchase examinations (PPE) a logical next step. Therefore, there is a need to have more understanding of asymmetry during a PPE in horses described on clinical evaluation as subtly lame.Objectives The objective of this study is to objectively compare asymmetry in horses raising minor vet concerns in a PPE and in horses raising major vet concerns with that found in horses presented with subtle single-limb lameness, and to investigate the effect of age/discipline on the clinicians' interpretation of asymmetry on the classification of minor vet concerns in a PPE.Study Design Clinical case-series.Methods Horses presented for PPE (n = 98) or subjectively evaluated as single limb low-grade (1-2/5) lame (n = 24, 13 forelimb lame, 11 hindlimb lame), from the patient population of a single clinic, were enrolled in the study provided that owners were willing to participate. Horses undergoing PPE were assigned a classification of having minor vet concerns (n = 84) or major vet concerns (n = 14) based on findings during the dynamic-orthopaedic part of the PPE. Lame horses were only included if pain-related lameness was confirmed by an objective improvement after diagnostic analgesia exceeding daily variation determined for equine symmetry parameters using optical motion capture. Clinical evaluation was performed by six different clinicians, each with >= 8 years of equine orthopaedic experience. Vertical movement symmetry was measured using optical motion capture, simultaneously with the orthopaedic examination. Data were analysed using previously described parameters and mixed model analysis and least squares means were used to calculate differences between groups.Results There was no effect of age or discipline on the levels of asymmetry within PPE horses raising minor vet concerns. MinDiff and RUD of the head discriminated between forelimb lame and PPE horses raising minor vet concerns; MinDiff, MaxDiff, RUD of the Pelvis, HHDswing and HHDstance did so for hindlimb lameness. Two lameness patterns differentiated both forelimb and hindlimb lame from PPE horses with minor vet concerns: RUD Poll + MinDiff Withers - RUD Pelvis and RUD Pelvis + RUD Poll - MinDiff Withers. Correcting for vertical range of motion enabled differentiation of PPE horses with minor vet concerns from PPE horses with major vet concerns.Main Limitations Objective data only based on trot on soft surface, limited number of PPE horses with major vet concerns.Conclusions Combinations of kinematic parameters discriminate between PPE horses with minor vet concerns and subtly lame horses, though overlap exists