16 results on '"M. Mahmoodi Darian"'
Search Results
2. He-tagging spectroscopy of tetracene cations*
- Author
-
M. Kappe, B. Rasul, M. Mahmoodi-Darian, A. Schiller, F. Zappa, S. A. Krasnokutski, and P. Scheier
- Subjects
Biophysics ,Physical and Theoretical Chemistry ,Condensed Matter Physics ,Molecular Biology - Published
- 2023
3. The Influence of Resonance Helical Field on the Z eff and Impurity Radiation in IR-T1 Tokamak
- Author
-
M. Mahmoodi Darian, A. Hojabri, M. Ghoranneviss, and Mohammad Kazem Salem
- Subjects
Nuclear and High Energy Physics ,Tokamak ,Materials science ,Field (physics) ,Resonance ,Plasma ,Radiation ,law.invention ,Ion ,Nuclear Energy and Engineering ,Physics::Plasma Physics ,law ,Impurity ,Nuclear fusion ,Atomic physics - Abstract
The influence of resonant helical field, RHF, on effective ion charge, Zeff, and impurity radiations on IR-T1 tokamak discharges was studied. The theoretical calculation of Zeff with RHF indicated that the Zeff decreased. To observe the effects of reduced Zeff on impurity radiation, two important parts of plasma were investigated, equilibrium region of plasma and disruptive plasma. The results obtained from previous experiments on equilibrium plasma showed the increased radiation of impurities, in comparison with preceding and next regions, whereas the new results indicate that the impurities radiation decreases remarkably in disruptive part of plasma.
- Published
- 2006
4. Experimental Study of Plasma Materials' Interaction in Plasma Focus 'Dena'
- Author
-
M. V. Roshan and M. Mahmoodi Darian
- Subjects
Nuclear and High Energy Physics ,Tokamak ,Materials science ,Dense plasma focus ,Nuclear engineering ,Plasma ,Fusion power ,law.invention ,Nuclear physics ,Interaction studies ,Nuclear Energy and Engineering ,Material selection ,law ,Nuclear fusion ,Neutron - Abstract
It is widely recognized that plasma material interaction in fusion devices is a critical issue that affects the overall machine performance. The process of material selection with a low degradation effect on the confined plasma and on the nuclear fusion production in tokamaks is of great importance. However, plasma materials' interaction studies in tokamaks have some limitations, so it is suggested that a new method for investigating this phenomenon be developed. The high capabilities of plasma focus devices allow one to simulate the interaction studies of tokamak plasma and first-wall materials. Our experiments were performed on a 90-kJ Filippov-type plasma focus, Dena. Experimental results clearly show the influence of materials on the neutron yield and neutron production mechanisms.
- Published
- 2003
5. Calculation ofZ eff from plasma resistivity in IR-T1 tokamak
- Author
-
Mohammad Kazem Salem, R. Arvin, M. Mahmoodi Darian, and M. Ghoranneviss
- Subjects
Physics ,Tokamak ,Divertor ,Bremsstrahlung ,General Physics and Astronomy ,Charge (physics) ,Plasma ,law.invention ,Ion ,Nuclear physics ,law ,Electrical resistivity and conductivity ,Atomic physics ,Anomaly (physics) - Abstract
The effective ion charge,Z eff, represents the average charge of ionsZ i of gasses inside the system, which indicates the level of the impurities in the plasma. Several techniques have been applied to estimateZ eff, like mass spectroscopy, anomaly factor and Bremsstrahlung radiation. We estimatedZ eff in the IR-T1 tokamak through anomaly factor. The IR-T1 tokamak is a small air-core transformer tokamak with circular cross section and with out conducting shell and divertor. Its aspect ratio is $$\frac{R}{a} = \frac{{45 cm}}{{12.5 cm}}.$$ For a tokamak discharge of 30 kA plasma current and 1.5 V of loop voltage and by anomaly factor we observed thatZ eff value is about 1.5.
- Published
- 2004
6. Doubly charged dimers and trimers of heavy noble gases.
- Author
-
Schöpfer G, Bergmeister S, Ončák M, Stromberg I, Mahmoodi-Darian M, Scheier P, Echt O, and Gruber E
- Abstract
Many doubly charged heteronuclear dimers are metastable or even thermodynamically stable with respect to charge separation. Homonuclear dicationic dimers, however, are more difficult to form. He
2 2+ was the first noble gas dimer predicted to be metastable and, decades later, observed. Ne2 2+ is the only other dicationic noble gas dimer that has been detected so far. Here, we present a novel approach to form fragile dicationic species, by post-ionization of singly charged ions that are embedded in helium nanodroplets (HNDs). Bare ions are then extracted by colliding the HNDs with helium gas. We detect homonuclear doubly charged dimers and trimers of krypton and xenon, but not argon. Our multi-reference ab initio calculations confirm the stability of Kr2 2+ , Kr3 2+ , Xe2 2+ , Xe3 2+ , and Ar2 2+ , but put the stability of Ar3 2+ towards dissociation to Ar+ + Ar2 + into question.- Published
- 2024
- Full Text
- View/download PDF
7. Solvation of cationic copper clusters in molecular hydrogen.
- Author
-
Lushchikova OV, Reichegger J, Kollotzek S, Zappa F, Mahmoodi-Darian M, Bartolomei M, Campos-Martínez J, González-Lezana T, Pirani F, and Scheier P
- Abstract
Multiply charged superfluid helium nanodroplets are utilized to facilitate the growth of cationic copper clusters (Cu
n + , where n = 1-8) that are subsequently solvated with up to 50 H2 molecules. Production of both pristine and protonated cationic Cu clusters are detected mass spectrometrically. A joint effort between experiment and theory allows us to understand the nature of the interactions determining the bonding between pristine and protonated Cu+ and Cu2 + cations and molecular hydrogen. The analysis reveals that in all investigated cationic clusters, the primary solvation shell predominantly exhibits a covalent bonding character, which gradually decreases in strength, while for the subsequent shells an exclusive non-covalent behaviour is found. Interestingly, the calculated evaporation energies associated with the first solvation shell markedly surpass thermal values, positioning them within the desirable range for hydrogen storage applications. This comprehensive study not only provides insights into the solvation of pristine and protonated cationic Cu clusters but also sheds light on their unique bonding properties.- Published
- 2023
- Full Text
- View/download PDF
8. Structure and formation of copper cluster ions in multiply charged He nanodroplets.
- Author
-
Lushchikova OV, Gatchell M, Reichegger J, Kollotzek S, Zappa F, Mahmoodi-Darian M, and Scheier P
- Abstract
The structure of cationic and anionic Cu clusters grown in multiply charged superfluid He nanodroplets was investigated using He tagging as a chemical probe. Further, the structure assignment was done based on the magic-numbered ions, representing the most energetically favorable structures. The exact geometry of the cluster and positions of He is verified by calculations. It was found that the structure of the clusters grown in the He droplets is similar to that produced with a laser ablation source and the lowest energy structures predicted by theoretical investigations. The only difference is the structure of the Cu
5 + , which in our experiments has a twisted-X geometry, rather than a bipyramid or planar half-wheel geometry suggested by previous studies. This might be attributed to the different cluster formation mechanisms, the absence of the Ar-tag and the ultracold environment. It was also found that He tends to bind to partially more electro-negative or positive areas of the anionic or cationic clusters, respectively.- Published
- 2023
- Full Text
- View/download PDF
9. Complexes with Atomic Gold Ions: Efficient Bis-Ligand Formation.
- Author
-
Duensing F, Gruber E, Martini P, Goulart M, Gatchell M, Rasul B, Echt O, Zappa F, Mahmoodi-Darian M, and Scheier P
- Abstract
Complexes of atomic gold with a variety of ligands have been formed by passing helium nanodroplets (HNDs) through two pickup cells containing gold vapor and the vapor of another dopant, namely a rare gas, a diatomic molecule (H
2 , N2 , O2 , I2 , P2 ), or various polyatomic molecules (H2 O, CO2 , SF6 , C6 H6 , adamantane, imidazole, dicyclopentadiene, and fullerene). The doped HNDs were irradiated by electrons; ensuing cations were identified in a high-resolution mass spectrometer. Anions were detected for benzene, dicyclopentadiene, and fullerene. For most ligands L, the abundance distribution of AuLn + versus size n displays a remarkable enhancement at n = 2. The propensity towards bis-ligand formation is attributed to the formation of covalent bonds in Au+ L2 which adopt a dumbbell structure, L-Au+ -L, as previously found for L = Xe and C60 . Another interesting observation is the effect of gold on the degree of ionization-induced intramolecular fragmentation. For most systems gold enhances the fragmentation, i.e., intramolecular fragmentation in AuLn + is larger than in pure Ln + . Hydrogen, on the other hand, behaves differently, as intramolecular fragmentation in Au(H2 )n + is weaker than in pure (H2 )n + by an order of magnitude.- Published
- 2021
- Full Text
- View/download PDF
10. Solvation of Silver Ions in Noble Gases He, Ne, Ar, Kr, and Xe.
- Author
-
Mahmoodi-Darian M, Martini P, Tiefenthaler L, Kočišek J, Scheier P, and Echt O
- Abstract
We use a novel technique to solvate silver cations in small clusters of noble gases. The technique involves the formation of large, superfluid helium nanodroplets that are subsequently electron ionized, mass-selected by deflection in an electric field, and doped with silver atoms and noble gases (Ng) in pickup cells. Excess helium is then stripped from the doped nanodroplets by multiple collisions with helium gas at room temperature, producing cluster ions that contain no more than a few dozen noble gas atoms and just a few (or no) silver atoms. Under gentle stripping conditions, helium atoms remain attached to the cluster ions, demonstrating their low vibrational temperature. Under harsher stripping conditions, some of the heavier noble gas atoms will be evaporated as well, thus enriching stable clusters of Ng
n Agm + at the expense of less stable ones. This results in local anomalies in the cluster ion abundance, which is measured in a high-resolution time-of-flight mass spectrometer. On the basis of these data, we identify specific "magic" sizes n of particularly stable ions. There is no evidence, however, for enhanced stability of Ng2 Ag+ , in contrast to the high stability of Ng2 Au+ that derives from the covalent nature of the bond for heavy noble gases. "Magic" sizes are also identified for Ag2 + dimer ions complexed with He or Kr. Structural models will be tentatively proposed. A sequence of magic numbers n = 12, 32, and 44, indicative of three concentric solvation shells of icosahedral symmetry, is observed for Hen H2 O+ .- Published
- 2019
- Full Text
- View/download PDF
11. Electron Attachment and Electron Ionization of Formic Acid Clusters Embedded in Helium Nanodroplets.
- Author
-
Mahmoodi-Darian M, Lundberg L, Zöttl S, Scheier P, and Echt O
- Abstract
We report the results of an experimental study of electron ionization of large helium nanodroplets doped with formic acid (FA). Several homologous series of cluster anions are observed, including [FA
n -H]- , undissociated FAn - , and these ions complexed with one or more H2 O. Some major features resemble those observed upon sputtering of frozen FA films but they differ significantly from results obtained by electron attachment to bare FA clusters in the gas phase. The FAn - and (H2 O)[FAn -H]- series show abrupt onsets above n = 2 and 5, respectively. A prominent resonance in the anion yield occurs at 22.5 eV due to the formation of an intermediate He-* . Also observed are homologous series of [FA-H]- or [FA2 -H]- complexed with helium. The cation chemistry is dominated by the production of protonated formic acid clusters, [FAn H]+ , but various other homologous cluster ion series are observed as well. Graphical Abstract.- Published
- 2019
- Full Text
- View/download PDF
12. Uptake and accommodation of water clusters by adamantane clusters in helium droplets: interplay between magic number clusters.
- Author
-
Kranabetter L, Martini P, Gitzl N, Kuhn M, Saleem F, Rasul B, Mahmoodi Darian M, Jabbour Al Maalouf E, Sukuba I, Kaiser A, Goulart M, Böhme DK, and Scheier P
- Abstract
We report an experimental study of water clusters as guests in interactions with clusters of adamantane (Ad) as hosts that occur in doped helium droplets at extremely low temperatures. Separate experiments with pure water as dopant showed ready formation of a distribution of water clusters (H2O)mH+ that peaks at m = 11 and extends beyond m = 100 with local maxima at m = 4, 11, 21, 28 and 30 with (H2O)21H+ being the most anomalous and showing the greatest stability with respect to clusters immediately adjacent in water content. When adamantane is also added as a dopant, extensive hydration is seen in the formation of water/adamantane clusters, (H2O)mAdn+; magic number clusters (H2O)21Adn+ are seen for all the adamantane clusters. Other magic numbers for water clusters attached to adamantane, (H2O)mAdn+, are as for pristine protonated water, with m = 28 and m = 30. The icosahedral shell closure of pure adamantane at n = 13 and 19 appears to be preserved with (H2O)21 replacing one adamantane. (H2O)21Ad12+ and (H2O)21Ad18+ stand out in intensity and demonstrate the interplay of magic number water clusters with magic number adamantane clusters, observed perhaps for the first time in gas-phase cluster chemistry. There was no clear evidence for the formation of clathrate hydrates in which adamantane is trapped within structured water.
- Published
- 2018
- Full Text
- View/download PDF
13. Doubly charged coronene clusters-Much smaller than previously observed.
- Author
-
Mahmoodi-Darian M, Raggl S, Renzler M, Goulart M, Huber SE, Mauracher A, Scheier P, and Echt O
- Abstract
The smallest doubly charged coronene cluster ions reported so far, Cor
15 2+ , were produced by charge exchange between bare coronene clusters and He2+ [H. A. B. Johansson et al., Phys. Rev. A 84, 043201 (2011)]. These dications are at least five times larger than the estimated Rayleigh limit, i.e., the size at which the activation barrier for charge separation vanishes. Such a large discrepancy is unheard of for doubly charged atomic or molecular clusters. Here we report the mass spectrometric observation of doubly charged coronene trimers, produced by electron ionization of helium nanodroplets doped with coronene. The observation implies that Cor3 2+ features a non-zero fission barrier too large to overcome under the present experimental conditions. The height of the barriers for the dimer and trimer has been estimated by means of density functional theory calculations. A sizeable barrier for the trimer has been revealed in agreement with the experimental findings.- Published
- 2018
- Full Text
- View/download PDF
14. Temperature dependence of dissociative electron attachment to bromo-chlorotoluene isomers: Competition between detachment of Cl - and Br .
- Author
-
Mahmoodi-Darian M, Huber SE, Mauracher A, Probst M, Denifl S, Scheier P, and Märk TD
- Abstract
Dissociative electron attachment to three isomers of bromo-chlorotoluene was investigated in the electron energy range from 0 to 2 eV for gas temperatures in the range of 392-520 K using a crossed electron-molecular beam apparatus with a temperature regulated effusive molecular beam source. For all three molecules, both Cl
- and Br- are formed. The ion yields of both halogenides show a pronounced temperature effect. In the case of Cl- and Br- , the influence of the gas temperature can be observed at the threshold peak close to 0 eV. The population of molecules that have some of their out-of-plane modes excited varies strongly in the temperature range investigated, indicating that such vibrations might play a role in the energy transfer towards bond breaking. Potential energy curves for the abstraction of Cl- and Br- were calculated and extrapolated into the metastable domain. The barriers in the diabatic curves approximated in this way agree well with the ones derived from the temperature dependence observed in the experiments.- Published
- 2018
- Full Text
- View/download PDF
15. Study of Electron Ionization and Fragmentation of Non-hydrated and Hydrated Tetrahydrofuran Clusters.
- Author
-
Neustetter M, Mahmoodi-Darian M, and Denifl S
- Subjects
- DNA chemistry, Dimerization, Electrons, Equipment Design, Ions chemistry, Mass Spectrometry instrumentation, Mass Spectrometry methods, Models, Molecular, Water chemistry, Furans chemistry
- Abstract
Mass spectroscopic investigations on tetrahydrofuran (THF, C
4 H8 O), a common model molecule of the DNA-backbone, have been carried out. We irradiated isolated THF and (hydrated) THF clusters with low energy electrons (electron energy ~70 eV) in order to study electron ionization and ionic fragmentation. For elucidation of fragmentation pathways, deuterated TDF (C4 D8 O) was investigated as well. One major observation is that the cluster environment shows overall a protective behavior on THF. However, also new fragmentation channels open in the cluster. In this context, we were able to solve a discrepancy in the literature about the fragment ion peak at mass 55 u in the electron ionization mass spectrum of THF. We ascribe this ion yield to the fragmentation of ionized THF clusters. Graphical Abstract ᅟ.- Published
- 2017
- Full Text
- View/download PDF
16. Temperature effects on the dissociative electron attachment to dichlorobenzene isomers.
- Author
-
Mahmoodi-Darian M, Mauracher A, Aleem A, Denifl S, Rittenschober B, Bacher A, Probst M, Märk TD, and Scheier P
- Abstract
Dissociative electron attachment to all three isomers of dichlorobenzene has been investigated in the electron energy range from 0 to 2 eV and in the gas temperature range from 391 to 696 K using a crossed electron-molecular beam apparatus with a new temperature-regulated effusive molecular beam source. In the case of the dissociative electron attachment channel Cl(-)/1,2-dichlorobenzene and Cl(-)/1,4-dichlorobenzene, strong enhancement of the negative ion production with the gas temperature at low electron energies has been observed. The low-energy peak increases dramatically when the gas temperature is raised from 391 to 696 K. Activation energies for dissociative electron attachment of (482 +/- 20) meV for 1,2-dichlorobenzene and (59 +/- 20) meV for 1,4-dichlorobenzene have been determined. For the resonance at (0.49 +/- 0.03) eV in 1,2-dichlorobenzene and (0.32 +/- 0.03) eV in 1,4-dichlorobenzene, no dependence of the cross sections on the gas temperature has been observed. In the case of the dissociative electron attachment to Cl(-)/1,3-dichlorobenzene, the cross section does not depend on the temperature in the electron energy range from 0 to 2 eV. Quantum chemical calculations of the reaction energies and of the potential energy curves involved in the dissociation of Cl(-) have been performed, together with an analysis of the thermo dynamical accessibility of the relevant vibrational modes. Possible reasons for the different temperature dependences of the isomers are discussed.
- Published
- 2009
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.