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Tilmann D. Märk

Bio: Tilmann D. Märk is an academic researcher from University of Innsbruck. The author has contributed to research in topics: Electron ionization & Ion. The author has an hindex of 64, co-authored 662 publications receiving 18712 citations. Previous affiliations of Tilmann D. Märk include University of New Hampshire & Claude Bernard University Lyon 1.


Papers
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Journal ArticleDOI
TL;DR: In this article, the Tofwerk orthogonal acceleration reflectron time-of-flight (TOF-MS) was used to measure VOCs at ultra-low concentrations (as low as a few pptv) under high mass resolution (as high as 6000m/Δm in the V-mode) with a mass range of beyond 100,000 amu.

514 citations

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TL;DR: It is demonstrated that electrons at energies below the threshold for electronic excitation effectively decompose gas phase uracil generating a mobile hydrogen radical and the corresponding closed shell uracils fragment anion (U-H)(-).
Abstract: The interaction of high energy radiation (� , � , � rays or heavy ions) with living cells does not in general directly lead to DNA strand breaks. The primary interaction essentially removes electrons from the components of the complex molecular network, i.e., electrons from valence states of the chemical bonds but also electrons from localized inner shells of the individual atoms. As a result of the subsequent charge transfer and energy dissipating processes, chemical bonds can be ruptured generating neutral or ionic radicals as additional secondary species. Electrons as the most abundant secondary species are created with an estimated quantity of � 4 � 10 4 electrons per MeV primary quantum deposited [1]. The larger majority possesses initial kinetic energies up to about 20 eV [2]. In the course of successive inelastic collisions within the medium they are thermalized within 10 � 12 s before they reach some stage of solvation, then as chemical rather inactive species. Moreover, damage of the genom in a living cell by ionizing radiation is about one-third direct and two-thirds indirect [3]. Direct damage concerns reactions directly in the DNA and its closely bound water molecules and indirect damage results from energy deposition in water molecules and other biomolecules in the surrounding of the DNA. It is believed that almost all the indirect damage is due to the attack of the highly reactive hydroxyl radical [4,5]. The importance of reactions of presolvated electrons with amino acids and nucleotides has already been pointed out more than two decades ago by time resolved pulse radiolysis experiments [6]. More recently, the ability of free ballistic electrons (3‐20 eV) to efficiently induce single and double strand breaks in supercoiled DNA has clearly been shown by Sanche and co-workers [7]. In these studies it was demonstrated that the DNA strand breaks were initiated by the formation and decay of transient negative ion (TNI) states, localized on the various DNA components (base, phosphate, deoxyribose, or hydration water). Resonances in DNA strand break curves were observed in the energy range around 10 eV ,s imilar to those TNI states formed by these components in the gas phase or in homogeneous films as exemplified in Ref. [7]

290 citations

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TL;DR: A recent review as discussed by the authors describes recent progress in the development of more rigorous approaches for the calculation of absolute electron-impact molecular ionization cross sections, particularly in applications where a larger number of cross section data were needed with reasonable precision.

264 citations

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TL;DR: PTR-ToF-MS can successfully be used to estimate reaction rate coefficients between H(3)O(+) and VOC at PTR-MS working conditions and find good agreement with the corresponding nonthermal theoretical predictions.
Abstract: Proton transfer reaction - mass spectrometry (PTR-MS) has become a reference technique in environmental science allowing for VOC monitoring with low detection limits. The recent introduction of time-of-flight mass analyzer (PTR-ToF-MS) opens new horizons in terms of mass resolution, acquisition time, and mass range. A standard procedure to perform quantitative VOC measurements with PTR-ToF-MS is to calibrate the instrument using a standard gas. However, given the number of compounds that can be simultaneously monitored by PTR-ToF-MS, such a procedure could become impractical, especially when standards are not readily available. In the present work we show that, under particular conditions, VOC concentration determinations based only on theoretical predictions yield good accuracy. We investigate a range of humidity and operating conditions and show that theoretical VOC concentration estimations are accurate when the effect of water cluster ions is negligible. We also show that PTR-ToF-MS can successfully be used to estimate reaction rate coefficients between H(3)O(+) and VOC at PTR-MS working conditions and find good agreement with the corresponding nonthermal theoretical predictions. We provide a tabulation of theoretical rate coefficients for a number of relevant volatile organic compounds at various energetic conditions and test the approach in a laboratory study investigating the oxidation of alpha-pinene.

249 citations

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TL;DR: In this paper, a new approach to mass spectrometric measurement and analysis has been used to study the electron impact ionization of the rare gases in the low electron energy regime (<180 eV).
Abstract: A new approach to mass spectrometric measurement and analysis has been used to study the electron impact ionization of the rare gases in the low electron energy regime (<180 eV). Critical considerations are given to the problems of ion extraction from the ion source (Nier‐type) and the transmission of the extracted ions through the mass spectrometer system (double focusing sector field Varian MAT CH5). Accurate relative partial cross section functions were obtained for production of He+ and He2+ from He; Ne+, Ne2+, and Ne3+ from Ne; Ar+, Ar2+, Ar3+ from Ar, and Kr+, Kr2+, Kr3+ and Kr4+ from Kr. In addition, the cross section ratios for the partial ionization cross sections of each individual gas were determined. These ratios were used to sum up the relative partial cross section functions for each gas, hence obtaining relative total ionization cross section functions by weighting each partial cross section function with the respective charge number. The shape of the relative total ionization cross section...

218 citations


Cited by
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Journal ArticleDOI
Rolf Sander1
TL;DR: According to Henry's law, the equilibrium ratio between the abundances in the gas phase and in the aqueous phase is constant for a dilute solution as discussed by the authors, and a compilation of 17 350 values of Henry's Law constants for 4632 species, collected from 689 references is available at http://wwwhenrys-law.org
Abstract: Many atmospheric chemicals occur in the gas phase as well as in liquid cloud droplets and aerosol particles Therefore, it is necessary to understand the distribution between the phases According to Henry's law, the equilibrium ratio between the abundances in the gas phase and in the aqueous phase is constant for a dilute solution Henry's law constants of trace gases of potential importance in environmental chemistry have been collected and converted into a uniform format The compilation contains 17 350 values of Henry's law constants for 4632 species, collected from 689 references It is also available at http://wwwhenrys-laworg

1,935 citations

Journal ArticleDOI
TL;DR: In this article, the time dependence of ρ11, ρ22 and ρ12 under steady-state conditions was analyzed under a light field interaction V = -μ12Ee iωt + c.c.
Abstract: (b) Write out the equations for the time dependence of ρ11, ρ22, ρ12 and ρ21 assuming that a light field interaction V = -μ12Ee iωt + c.c. couples only levels |1> and |2>, and that the excited levels exhibit spontaneous decay. (8 marks) (c) Under steady-state conditions, find the ratio of populations in states |2> and |3>. (3 marks) (d) Find the slowly varying amplitude ̃ ρ 12 of the polarization ρ12 = ̃ ρ 12e iωt . (6 marks) (e) In the limiting case that no decay is possible from intermediate level |3>, what is the ground state population ρ11(∞)? (2 marks) 2. (15 marks total) In a 2-level atom system subjected to a strong field, dressed states are created in the form |D1(n)> = sin θ |1,n> + cos θ |2,n-1> |D2(n)> = cos θ |1,n> sin θ |2,n-1>

1,872 citations

Journal ArticleDOI
TL;DR: In this paper, a proton transfer reaction mass spectrometer (PTR-MS) was developed which allows for on-line measurements of trace components with concentrations as low as a few pptv.

1,542 citations

Journal ArticleDOI
TL;DR: In this paper, a review of the observed mid-IR spectral properties of polycyclic aromatic hydrocarbons (PAHs) is presented, emphasizing the contribution of these species to photoelectric heating and the ionization balance of the interstellar gas and to the formation of small hydrocarbon radicals and carbon chains.
Abstract: Large polycyclic aromatic hydrocarbon (PAH) molecules carry the infrared (IR) emission features that dominate the spectra of most galactic and extragalactic sources. This review surveys the observed mid-IR characteristics of these emission features and summarizes laboratory and theoretical studies of the spectral characteristics of PAHs and the derived intrinsic properties of emitting interstellar PAHs. Dedicated experimental studies have provided critical input for detailed astronomical models that probe the origin and evolution of interstellar PAHs and their role in the universe. The physics and chemistry of PAHs are discussed, emphasizing the contribution of these species to the photoelectric heating and the ionization balance of the interstellar gas and to the formation of small hydrocarbon radicals and carbon chains. Together, these studies demonstrate that PAHs are abundant, ubiquitous, and a dominant force in the interstellar medium of galaxies.

1,473 citations

Journal ArticleDOI
TL;DR: This paper presented an up-to-date, comprehensive tabulation of EF for known pyrogenic species based on measurements made in smoke that has cooled to ambient temperature, but not yet undergone significant photochemical processing.
Abstract: . Biomass burning (BB) is the second largest source of trace gases and the largest source of primary fine carbonaceous particles in the global troposphere. Many recent BB studies have provided new emission factor (EF) measurements. This is especially true for non-methane organic compounds (NMOC), which influence secondary organic aerosol (SOA) and ozone formation. New EF should improve regional to global BB emissions estimates and therefore, the input for atmospheric models. In this work we present an up-to-date, comprehensive tabulation of EF for known pyrogenic species based on measurements made in smoke that has cooled to ambient temperature, but not yet undergone significant photochemical processing. All EFs are converted to one standard form (g compound emitted per kg dry biomass burned) using the carbon mass balance method and they are categorized into 14 fuel or vegetation types. Biomass burning terminology is defined to promote consistency. We compile a large number of measurements of biomass consumption per unit area for important fire types and summarize several recent estimates of global biomass consumption by the major types of biomass burning. Post emission processes are discussed to provide a context for the emission factor concept within overall atmospheric chemistry and also highlight the potential for rapid changes relative to the scale of some models or remote sensing products. Recent work shows that individual biomass fires emit significantly more gas-phase NMOC than previously thought and that including additional NMOC can improve photochemical model performance. A detailed global estimate suggests that BB emits at least 400 Tg yr−1 of gas-phase NMOC, which is almost 3 times larger than most previous estimates. Selected recent results (e.g. measurements of HONO and the BB tracers HCN and CH3CN) are highlighted and key areas requiring future research are briefly discussed.

1,472 citations