| 1. |
- Andersson, Patrik U, 1970, et al.
(författare)
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Isotope exchange and structural rearrangements in reactions between size-selected ionic water clusters, H3O+(H2O)n and NH4+(H2O)n, and D2O
- 2008
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Ingår i: Phys.Chem.Chem.Phys. - : Royal Society of Chemistry (RSC). ; 10, s. 6127-6134
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen/deuterium exchange in reactions of H3O+(H2O)n and NH4+(H2O)n (1 n 30) with D2O has been studied experimentally at center-of-mass collisions energies of 0.2 eV. For a given cluster size, the cross-sections for H3O+(H2O)n and NH4+(H2O)n are similar, indicating a structural resemblance and energetics of binding. For protonated pure water clusters, H3O+(H2O)n, reacting with D2O the main H/D exchange mechanism is found to be proton catalyzed. In addition the H/D scrambling becomes close to statistically randomized for the larger clusters. For NH4+(H2O)n clusters reacting with D2O, the main mechanism is a D2O/H2O swap reaction. The lifetimes of H3O+(H2O)n clusters have been estimated using RRKM theory and a plateau in lifetime vs. cluster size is found already at n = 10.
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| 2. |
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| 3. |
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| 4. |
- Fathi, Pantea, 1984-
(författare)
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Ion-neutral reactions of C2H2N+ with hydrocarbons : relevant to Titan’s ionosphere
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To provide some insights on the formation of long-chain carbon-nitrogen bearing ions in Titan’s atmosphere, laboratory measurements of ion-neutral reactions were conducted and results are presented in the following licentiate thesis. The product ions of the C2H2N+ reaction with saturated and unsaturated neutral hydrocarbons have been studied using guided ion beam mass spectrometer (GIB-MS). The data have been used to infer the product ion signal intensity dependences on pressure and collision energies to obtain information on the reactions contributing to these signals. Theoretical calculations have been carried out to interpret these measurements and to elucidate the reaction pathways leading to the observed product ions. This study provides understanding on the formation of long-chain carbon-nitrogen bearing ions through exothermic and barrierless ion-neutral reactions which are of interest as possible formation routes to heavy positive ions detected in Titan’s atmosphere by Cassini’s ion neutral mass spectrometer (INMS).
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| 5. |
- Hansen, Klavs, 1958, et al.
(författare)
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Activation energies for evaporation from protonated and deprotonated water clusters from mass spectra
- 2009
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Ingår i: journal of chemical physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 131
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Tidskriftsartikel (refereegranskat)abstract
- Experimental mass abundance spectra are used to extract evaporative activation energies (dissociation energies) for protonated water clusters, (H$_2$O)$_N$H$^+$, and deprotonated water clusters, (H$_2$O)$_N$ OH$^-$, in the size range up to hundred molecules. The inversion is achieved by application of the shell correction method adapted from nuclear physics to the abundance spectra. The well known abundance anomaly for protonated clusters which occurs for $N = 20-22$ is found to have the characteristic behavior of a shell closing, whereas other apparent magic numbers are only prominent peaks in the abundance spectra because of the instability of the evaporative precursor. For the deprotonated clusters, we find a similar shell closing for $N = 55-56$.
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| 6. |
- Hansen, Klavs, 1958, et al.
(författare)
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Magic numbers and stabilities of heavy water clusters,(D2O)ND+, N = 3 −48
- 2019
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Ingår i: International Journal of Mass Spectrometry. - : Elsevier BV. - 1387-3806. ; 440, s. 14-19
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Tidskriftsartikel (refereegranskat)abstract
- The abundance spectrum of deuterated heavy water clusters has been measured, and relative dissociationenergies were extracted from the abundances. The dissociation energies are similar to those of protonatedlight water clusters, except for a slightly reduced excess stability of the N = 21 cluster relative to the N = 22cluster. The difference is interpreted in terms of the special geometry of the N = 21 cluster. The absenceof a similar effect for N = 28/29 suggests that the stability of the N = 28 cluster is not due to a closed shellstructure
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| 7. |
- Lindén, Fredrik, 1988-
(författare)
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Mechanisms of Anion Reactions from the lab to ionospheres
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A multitude of heavy neutral and ionic molecules have been discovered by the Cassini Plasma Spectrometer in the ionosphere of Saturn's largest moon Titan. However, only three cyano anions were explicitly identified there, namely CN-, C3N- and C5N-. The identity of the heavier anions, which show an abundance maximum at m/z 1000, could, however, not be elucidated and there is, so far, no clear explanation how these were generated.We investigated the reaction of the cyanide anion with methyl iodide using a velocity map imaging spectrometer setup and ab initio calculations. The data indicate a dominant direct rebound mechanism and a high internal excitation of the neutral product. According to the ab initio calculation two possible reaction pathways were expected, but in the experiment the two channels turned out to be indistinguishable due to low resolution.We also studied the reaction between C3N- and acetylene using three different experimental setups: a triple quadrupole mass spectrometer, a tandem quadrupole mass spectrometer, and the ''CERISES'' guided ion beam apparatus.The reaction showed three primary reaction pathways leading to C2H-, CN-, and C5N-. The production of C2H- could either happen via proton transfer or via formation of an adduct. The appearance of CN- could be explained by a reaction sequence involving an intermediate adduct but also via collision induced dissociation. Even though ab initio calculations predict two exoergic pathways leading to CN- and C5N-, all products are only accessible via energy barriers above 1 eV.In addition, we investigated the reaction between C5N- and acetylene. Also in this case the experimental and theoretical studies revealed that all reaction pathways proceed via energy barriers well above 1 eV. The sole exoergic pathway leading to C7N- has an energy barrier of 1.91 eV. Since the chemistry in dark interstellar clouds and planetary ionospheres is restricted to exoergic reactions with energy barriers less than 20 meV or proceed in a barrier-less manner (Vuitton et al. Planetary and Space Science 57, 1558-1572 (2009)), none of the observed pathways are feasible growth mechanism in those environments.We also performed investigations of reactions between charged clusters with and without barriers using electrostatic models. This led to the development of both approximate and exact expressions, which describe the sphere-sphere interaction and the electron transfer from a (neutral or charged) dielectric sphere to another charged dielectric sphere. The exact solutions include sums that describe polarization effects to infinite orders. However, we have shown that these infinite sums can be simplified, and that these approximations can be applied to calculate the charge transfer cross-sections and Langevin-type cross-sections.
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| 8. |
- Rebrov, Oleksii, et al.
(författare)
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Chirally sensitive collision induced dissociation of proton-bound diastereomeric complexes of tryptophan and 2-butanol
- 2017
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Ingår i: Chirality. - : Wiley. - 0899-0042 .- 1520-636X. ; 29:3-4, s. 115-119
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Tidskriftsartikel (refereegranskat)abstract
- In this work we report the stereo-dependent collision-induced dissociation (CID) of proton-bound complexes of tryptophan and 2-butanol. The dissociation efficiency was measured as a function of collision energy in single collision mode. The homochiral complex was found to be less stable against CID than a heterochiral one. Additional gas dependence measurements were performed with diastereomeric complexes that confirm the findings.
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| 9. |
- Rebrov, Oleksii, 1988-, et al.
(författare)
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Non-covalently Bonded Diastereomeric Adducts of Amino Acids and (S)-1-Phenylethanol in Low-energy Dissociative Collisions
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We have studied the collision induced dissociation reactions of proton-bound diastereomeric adducts of S-(-)-1-phenylethanol and enantiomers of three different amino acids (tryptophan, phenylalanine, methionine) with argon at a collision energy of 0.5 eV in the center-of-mass frame. At this energy, fragmentation into the alcohol and the protonated amino acid was the only observed product channel. Contrary to anticipation, the fragmentation was found to be insensitive to the chirality of the constituents. The results obtained from quantum chemical calculations show that the hetero-chiral adducts are more stable than the homo-chiral forms. However, given the experimental conditions in the ion source, it is likely that multiple conformers which lie close in energy to the ground-state configuration are populated, limiting the experimental sensitivity to observe the predicted differences.
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| 10. |
- Ryding, Mauritz Johan, 1981, et al.
(författare)
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Isotope exchange in reactions between D2O and size-selected ionic water clusters containing pyridine, H+(pyridine)m(H2O)n
- 2011
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Ingår i: Physical Chemistry Chemical Physics. ; 13:4, s. 1356-1367
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Tidskriftsartikel (refereegranskat)abstract
- Pyridine contg. water clusters, H+(pyridine)m(H2O)n, have been studied both exptl. by a quadrupole time-of-flight mass spectrometer and by quantum chem. calcns. In the expts., H+(pyridine)m(H2O)n with m = 1-4 and n = 0-80 are obsd. For the cluster distributions obsd., there are no magic nos., neither in the abundance spectra, nor in the evapn. spectra from size selected clusters. Expts. with size-selected clusters H+(pyridine)m(H2O)n, with m = 0-3, reacting with D2O at a center-of-mass energy of 0.1 eV were also performed. The cross-sections for H/D isotope exchange depend mainly on the no. of water mols. in the cluster and not on the no. of pyridine mols. Clusters having only one pyridine mol. undergo D2O/H2O ligand exchange, while H+(pyridine)m(H2O)n, with m = 2, 3, exhibit significant H/D scrambling. These results are rationalized by quantum chem. calcns. (B3LYP and MP2) for H+(pyridine)1(H2O)n and H+(pyridine)2(H2O)n, with n = 1-6. In clusters contg. one pyridine, the water mols. form an interconnected network of hydrogen bonds assocd. with the pyridinium ion via a single hydrogen bond. For clusters contg. two pyridines, the two pyridine mols. are completely sepd. by the water mols., with each pyridine being positioned diametrically opposite within the cluster. In agreement with exptl. observations, these calcns. suggest a "see-saw mechanism" for pendular proton transfer between the two pyridines in H+(pyridine)2(H2O)n clusters. [on SciFinder (R)]
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