The Experts below are selected from a list of 294 Experts worldwide ranked by ideXlab platform
Dennis L. Lichtenberger - One of the best experts on this subject based on the ideXlab platform.
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the electronic states of 1 2 3 triazole studied by vacuum ultraviolet photoabsorption and ultraviolet photoelectron spectroscopy and a comparison with ab initio configuration interaction methods
Journal of Chemical Physics, 2011Co-Authors: Michael H. Palmer, S V Hoffmann, Ashley R Head, Nykola C. Jones, Dennis L. LichtenbergerAbstract:The Rydberg states in the vacuum ultraviolet photoabsorption spectrum of 1,2,3-triazole have been measured and analyzed with the aid of comparison to the UV valence photoelectron Ionizations and the results of ab initio configuration interaction (CI) calculations. Calculated electronic Ionization and excitation energies for singlet, triplet valence, and Rydberg states were obtained using multireference multiroot CI procedures with an aug-cc-pVTZ [5s3p3d1f] basis set and a set of Rydberg [4s3p3d3f] functions. Adiabatic excitation energies obtained for several electronic states using coupled-cluster (singles, doubles, and triples) and complete active space self-consistent field procedures agree well with experimental values. Variations in bond lengths with the electronic state are discussed. The lowest energy UV band (∼5.5–6.5 eV) is assigned to three electronically excited states and demonstrates the occurrence of a nonplanar upper state on the low energy side. A UV photoelectron spectrum with an improved ...
Herbert H Hill - One of the best experts on this subject based on the ideXlab platform.
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Evaluation of micro- versus nano-electrospray Ionization for ambient pressure ion mobility spectrometry
International Journal for Ion Mobility Spectrometry, 2012Co-Authors: Abu B. Kanu, Bharath S. Kumar, Herbert H HillAbstract:The comparison of nanospray and microspray Ionizations for detecting mixtures of compounds by ion mobility spectrometry has been investigated for sensitivity, ion transmission through a drift tube, and ion suppression effects when used as an Ionization source for ambient pressure ion mobility spectrometry (IMS). Several articles have demonstrated that nano-electrospray Ionization mass spectrometry (n-ESI-MS) has improved sensitivity, provides less background noise, and lower limits of detection than micro-electrospray Ionization (μ-ESI) for IMS. Most importantly, data from n-ESI-MS is concentration-sensitive. Our laboratory previously published an article that observed a striking result when μ-ESI-IMS was investigated for a single compound in the positive ion mode. The data reported was mass-sensitive. In this new investigation, we have investigated mixtures, and experiments were designed to evaluate the effect of sensitivity, ion transmission and ion suppressions in μ-ESI-IMS and n-ESI-IMS. At an electrospray flow rate in the μL min^−1 range, compounds with higher proton affinities responded best while at the nanospray flow rates of nL min^−1, relative responses were more equal. This study observed that a decreased ESI flow rate resulted in a decreased ion signal. These trends demonstrated less sensitivity for ESI-IMS at reduced flow rates but suggest better quantification. At higher flow rates, relative Ionization efficiencies were still uniform for all the components studied individually and in mixtures and sensitivity improved by about 78%. Concentration studies showed that at high concentrations, ion detection efficiencies were uniform at about 33% for all compounds studied individually and in mixtures. At low concentrations, the detection efficiency varied from 31% to 86%, depending on the proton affinity of the component in the mixture. Ion transmission through the IMS tube measured with a segmented Faraday detector that was incorporated into the IMS design indicated that most of the ion current for mixtures was transported through the IMS tube with a radius of less than 18 mm for both positive and negative ion modes.
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secondary Ionization of chemical warfare agent simulants atmospheric pressure ion mobility time of flight mass spectrometry
Analytical Chemistry, 2003Co-Authors: Wes E Steiner, Paul E Haigh, Brian H. Clowers, Herbert H HillAbstract:For the first time, the use of a traditional Ionization source for ion mobility spectrometry (radioactive nickel (63Ni) β emission Ionization) and three alternative Ionization sources (electrospray Ionization (ESI), secondary electrospray Ionization (SESI), and electrical discharge (corona) Ionization (CI)) were employed with an atmospheric pressure ion mobility orthogonal reflector time-of-flight mass spectrometer (IM(tof)MS) to detect chemical warfare agent (CWA) simulants from both aqueous- and gas-phase samples. For liquid-phase samples, ESI was used as the sample introduction and Ionization method. For the secondary Ionization (SESI, CI, and traditional 63Ni Ionization) of vapor-phase samples, two modes of sample volatilization (heated capillary and thermal desorption chamber) were investigated. Simulant reference materials, which closely mimic the characteristic chemical structures of CWA as defined and described by Schedule 1, 2, or 3 of the Chemical Warfare Convention treaty verification, were use...
Ralf Zimmermann - One of the best experts on this subject based on the ideXlab platform.
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comprehensive on line characterization of complex gas mixtures by quasi simultaneous resonance enhanced multiphoton Ionization vacuum uv single photon Ionization and electron impact Ionization in a time of flight mass spectrometer setup and instrumen
Analytical Chemistry, 2004Co-Authors: F Muhlberger, Klaus Hafner, S Kaesdorf, T Ferge, Ralf ZimmermannAbstract:This paper reports on a newly developed mobile mass spectrometer for comprehensive on-line analysis of complex gas mixtures such as ambient air or industrial process gases. Three Ionization methods, namely, the resonance-enhanced multiphoton Ionization (REMPI), vacuum-ultraviolet single-photon Ionization (SPI), and electron impact Ionization (EI) are implemented in this instrument and can be operated (quasi-) simultaneously. By means of this setup, a wide range of compounds can be analyzed due to the unique Ionization selectivitiy and sensitivity profiles provided by the different Ionization techniques. The mass spectrometer is designed for field application even under severe conditions. The REMPI technique is suitable for the selective and soft Ionization (without fragmentation) of aromatic compounds at trace level (ppbv/pptv). The also soft but less selective SPI technique with 118-nm vacuum-ultraviolet laser pulses is used as a second laser-based Ionization method. Mass spectra obtained by this technique show profiles of most organic compounds (aliphatic and aromatic species) and of some low IP inorganic substances (e.g., ammonia, nitrogen oxide) down to ppbv concentrations. In addition to the laser-based Ionization techniques, EI Ionization can be used for analysis of the bulk components such as water, oxygen, nitrogen, and carbon dioxide as well as for detection of inorganic minor components such as HCN or HCl from combustion flue gases at ppmv concentration levels. Each method yields specific mass spectrometric information of the sample composition. Special techniques have been developed to combine the three Ionization methods in a single mass spectrometer and to allow the quasi-parallel application of all three Ionization techniques.
Fumio Hirata - One of the best experts on this subject based on the ideXlab platform.
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theoretical study for partial molar volume of amino acids in aqueous solution implication of ideal fluctuation volume
Journal of Chemical Physics, 2000Co-Authors: T Imai, Masahiro Kinoshita, Fumio HirataAbstract:A Kirkwood–Buff equation for the partial molar volumes of polyatomic molecules in solutions is derived based on the reference interaction site model (RISM) theory of molecular liquids. The partial molar volume of the twenty amino acids in aqueous solution at infinite dilution are calculated using the equation, and the results are discussed in comparison with the experimental data. The results indicate that Ionizations of the C- and N-terminus groups give negative contributions to the volume ranging from −3.2 cm3/mol to −9.7 cm3/mol depending on the amino acid. Ionization of the dissociable residues also give negative contribution which ranges from −3.0 cm3/mol to −6.0 cm3/mol. On the other hand, contribution of the fractional charges on atoms to the volume is not necessarily negative, but rather slightly positive with few exceptions. It is clarified that contribution from an atom group to the volume is largely dependent on the situation where the group is placed. Therefore, it is concluded that the conven...
Michael H. Palmer - One of the best experts on this subject based on the ideXlab platform.
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the electronic states of 1 2 3 triazole studied by vacuum ultraviolet photoabsorption and ultraviolet photoelectron spectroscopy and a comparison with ab initio configuration interaction methods
Journal of Chemical Physics, 2011Co-Authors: Michael H. Palmer, S V Hoffmann, Ashley R Head, Nykola C. Jones, Dennis L. LichtenbergerAbstract:The Rydberg states in the vacuum ultraviolet photoabsorption spectrum of 1,2,3-triazole have been measured and analyzed with the aid of comparison to the UV valence photoelectron Ionizations and the results of ab initio configuration interaction (CI) calculations. Calculated electronic Ionization and excitation energies for singlet, triplet valence, and Rydberg states were obtained using multireference multiroot CI procedures with an aug-cc-pVTZ [5s3p3d1f] basis set and a set of Rydberg [4s3p3d3f] functions. Adiabatic excitation energies obtained for several electronic states using coupled-cluster (singles, doubles, and triples) and complete active space self-consistent field procedures agree well with experimental values. Variations in bond lengths with the electronic state are discussed. The lowest energy UV band (∼5.5–6.5 eV) is assigned to three electronically excited states and demonstrates the occurrence of a nonplanar upper state on the low energy side. A UV photoelectron spectrum with an improved ...
