75 research outputs found
Rotationally resolved threshold photoelectron spectra of OH and OD
The results of combined experimental and theoretical studies of the rotationally resolved photoelectron spectra of OH and OD following single‐photon ionization are presented. The measured zero‐kinetic‐energy (ZEKE) spectra were obtained using pulsed field ionization in conjunction with a vacuum ultraviolet laser source. The OH^+ and OD^+ (X ^3Σ^−, v^+=0) rotational distributions were studied over the range 95.0–95.4 nm. Agreement between the observed and calculated spectra is very encouraging. Improved values for the ionization potentials of OH and OD (104 989 and 105 085 ± 2 cm^(−1), respectively) are reported and the unusual dynamics favoring ΔN<0 transitions are discussed
Ion rotational distributions for near-threshold photoionization of H_2O
Ion rotational distributions for single‐photon VUV photoionization of the 1b_1 orbital of the X̃ ^1A_1 ground state of the jet‐cooled water are reported. These spectra reveal significant type a transitions which are seen to arise from odd angular momentum components of the photoelectron matrix element. The resulting photoionization dynamics are quite nonatomic‐like
A comparative study of the variables used to measure syntactic complexity and accuracy in task-based research
The constructs of complexity, accuracy and fluency (CAF) have been used extensively to investigate learner performance on second language tasks. However, a serious concern is that the variables used to measure these constructs are sometimes used conventionally without any empirical justification. It is crucial for researchers to understand how results might be different depending on which measurements are used, and accordingly, choose the most appropriate variables for their research aims. The first strand of this article examines the variables conventionally used to measure syntactic complexity in order to identify which may be the best indicators of different proficiency levels, following suggestions by Norris and Ortega. The second strand compares the three variables used to measure accuracy in order to identify which one is most valid. The data analysed were spoken performances by 64 Japanese EFL students on two picture-based narrative tasks, which were rated at Common European Framework of Reference for Languages (CEFR) A2 to B2 according to Rasch-adjusted ratings by seven human judges. The tasks performed were very similar, but had different degrees of what Loschky and Bley-Vroman term ‘task-essentialness’ for subordinate clauses. It was found that the variables used to measure syntactic complexity yielded results that were not consistent with suggestions by Norris and Ortega. The variable found to be the most valid for measuring accuracy was errors per 100 words. Analysis of transcripts revealed that results were strongly influenced by the differing degrees of task-essentialness for subordination between the two tasks, as well as the spread of errors across different units of analysis. This implies that the characteristics of test tasks need to be carefully scrutinised, followed by careful piloting, in order to ensure greater validity and reliability in task-based research
Selective Reagent Ion Mass Spectrometric Investigations of the Nitroanilines
This paper presents an investigation of proton and charge transfer reactions to 2-, 3- and 4-nitroanilines (C6H6N2O2) involving the reagent ions H3O+·(H2O)n (n=0, 1 and 2) and O2+, respectively, as a function of reduced electric field (60-240 Td), using Selective Reagent Ion-Time-of-Flight-Mass Spectrometry (SRI-ToF-MS). To aid in the interpretation of the H3O+·(H2O)n experimental data, the proton affinities and gas-phase basicities for the three nitroaniline isomers have been determined using density functional theory. These calculations show that proton transfer from both the H3O+ and H3O+·H2O reagent ions to the nitroanilines will be exoergic and hence efficient, with the reactions proceeding at the collisional rate. For proton transfer from H3O+ to the NO2 sites, the exoergicities are 171 kJ mol-1 (1.8 eV), 147 kJ mol-1 (1.5 eV) and 194 kJ mol-1 (2.0 eV) for 2-, 3- and 4-nitroanilines, respectively. Electron transfer from all three of the nitroanilines is also significantly exothermic by approximately 4 eV. Although a substantial transfer of energy occurs during the ion/molecule reactions, the processes are found to predominantly proceed via non-dissociative pathways over a large reduced electric field range. Only at relatively high reduced electric fields (>180 Td) is dissociative proton and charge transfer observed. Differences in fragment product ions and their intensities provide a means to distinguish the isomers, with proton transfer distinguishing 2-nitroaniline (2-NA) from 3- and 4-NA, and charge transfer distinguishing 4-NA from 2- and 3-NA, thereby providing a means to enhance selectivity using SRI-ToF-MS.(VLID)4826158Version of recor
Identification of gas-phase pyrolysis products in a prescribed fire: first detections using infrared spectroscopy for naphthalene, methyl nitrite, allene, acrolein and acetaldehyde
Volatile organic compounds (VOCs) are emitted from many sources, including
wildland fire. VOCs have received heightened emphasis due to such gases'
influential role in the atmosphere, as well as possible health effects. We
have used extractive infrared (IR) spectroscopy on recent prescribed burns
in longleaf pine stands and herein report the first detection of five
compounds using this technique. The newly reported IR detections include
naphthalene, methyl nitrite, allene, acrolein and acetaldehyde. We discuss
the approaches used for detection, particularly the software methods needed
to fit the analyte and multiple (interfering) spectral components within the
selected spectral micro-window(s). We also discuss the method's detection
limits and related parameters such as spectral resolution.</p
Vacuum-Ultraviolet Photoionization and Mass Spectrometric Characterization of Lignin Monomers Coniferyl and Sinapyl Alcohols
The fragmentation mechanisms of monolignols under various energetic processes are studied with jet-cooled thermal desorption molecular beam (TDMB) mass spectrometry (MS), 25 keV Bi3+ secondary ion MS (SIMS), synchrotron vacuum-ultraviolet secondary neutral MS (VUV-SNMS) and theoretical methods. Experimental and calculated appearance energies of fragments observed in TDMB MS indicate that the coniferyl alcohol photoionization mass spectra contain the molecular parent and several dissociative photoionization products. Similar results obtained for sinapyl alcohol are also discussed briefly. Ionization energies of 7.60 eV ? 0.05 eV for coniferyl alcohol and<7.4 eV for both sinapyl and dihydrosinapyl alcohols are determined. The positive ion SIMS spectrum of coniferyl alcohol shares few characteristic peaks (m/z = 137 and 151) with the TDMB mass spectra, shows extensive fragmentation, and does not exhibit clear molecular parent signals. VUV-SNMS spectra, on the other hand, are dominated by the parent ion and main fragments also present in the TDMB spectra. Molecular fragmentation in VUV-SNMS spectra can be reduced by increasing the extraction delay time. Some features resembling the SIMS spectra are also observed in the desorbed neutral products. The monolignol VUV-SNMS peaks shared with the TDMB mass spectra suggest that dissociative photoionization of ion-sputtered neutral molecules predominate in the VUV-SNMS mass spectra, despite the extra internal energy imparted in the initial ion impact. The potential applications of these results to imaging mass spectrometry of bio-molecules are discussed
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High resolution studies of atoms and small molecules
High resolution, continuous wave lasers have been utilized successfully in studies of small molecules. Examples of two-photon excitation schemes and of multiple resonance excitation sequences will be discussed within the framework of the spectroscopy and dynamics of selected Rydberg states of nitric oxide. Initial results on the circular dichroism of angular distributions in photoelectron spectra of individual hyperfine states of cesium will also be discussed, but no data given
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High resolution studies of atoms and small molecules
High resolution, continuous wave lasers have been utilized successfully in studies of small molecules. Examples of two-photon excitation schemes and of multiple resonance excitation sequences will be discussed within the framework of the spectroscopy and dynamics of selected Rydberg states of nitric oxide. Initial results on the circular dichroism of angular distributions in photoelectron spectra of individual hyperfine states of cesium will also be discussed, but no data given
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DYNAMOMETER EVALUATION OF PLASMA-CATALYST FOR DIESEL NOX REDUCTION
A three-stage plasma-catalyst system was developed and tested on an engine dynamometer. Previous laboratory testing suggested high NOx efficiency could be obtained. With hexene reductant added to the exhaust, over 90% NOx reduction was observed. However, with diesel or Fischer-Tropsch reductant the catalyst efficiency rapidly dropped off. Heating the catalyst in air removed brown deposit from the surface and restored conversion efficiency. Following the engine tests, the used catalysts were evaluated. BET surface area decreased, and TPD revealed significant storage. This storage appears to be partly unburned diesel fuel that can be removed by heating to around 250-300 C, and partly hydrocarbons bonded to the surface that remain in place until 450-500 C. Laboratory testing with propene reductant demonstrated that the catalyst regains efficiency slowly even when operating temperature does not exceed 300 C. This suggests that control strategies may be able to regenerate the catalyst by occasional moderate heating
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