Quantum state resolution and control in imaging of ion-molecule-reactions

way that chemical structures rearrange, chemical reaction dynamics, is a wonderful field of studies. This thesis aims to provide more detailed insights into the effect of the quantum nature of educts, reaction intermediates and products on the dynamics of ion-molecule reactions. Therefore, these reactions have been examined at increased resolution and with quantum state specific preparation of educts. In a first study, insight into quantum mechanical processes that influence the outcome of a reaction has been gained. By measurements of vibrational quantum state resolved angular differential cross-sections of reaction products, quantum state specific reaction dynamics in the reaction of Ar+ + N2 have been inferred. Further studies focused on the dynamics of bimolecular nucleophilic substitution (SN2) reactions, that play a pivotal role in chemical synthesis, especially for interchanging functional groups and for carbon-carbon bond formation. These dynamics are a main research focus of the Wester group. In this thesis, the reaction of F with CH3Cl has been studied and compared to earlier work on the reaction of F with CH3I. In this way, the influence of the leaving group on S N 2 reactions has been determined to infer its importance also regarding the transition state geometry and orientation effects. Checking beam overlaps of several beams is vital for the scattering experiments, especially when focused lasers are used to influence the molecular beam. In this thesis, a quantitative in-depth analysis of the imaging properties of this mode is presented. The description of the imaging process with Taylor matrices is very insightful and it has been recently extended to VMI settings. Finally, the question of how CH symmetric stretch vibrational excitation affects the reaction of F with CH3I has been tackled and the influence of vibrational excitation on an SN2 reaction has been directly imaged for the first time.way that chemical structures rearrange, chemical reaction dynamics, is a wonderful field of studies. This thesis aims to provide more detailed insights into the effect of the quantum nature of educts, reaction intermediates and products on the dynamics of ion-molecule reactions. Therefore, these reactions have been examined at increased resolution and with quantum state specific preparation of educts. In a first study, insight into quantum mechanical processes that influence the outcome of a reaction has been gained. By measurements of vibrational quantum state resolved angular differential cross-sections of reaction products, quantum state specific reaction dynamics in the reaction of Ar+ + N2 have been inferred. Further studies focused on the dynamics of bimolecular nucleophilic substitution (SN2) reactions, that play a pivotal role in chemical synthesis, especially for interchanging functional groups and for carbon-carbon bond formation. These dynamics are a main research focus of the Wester group. In this thesis, the reaction of F with CH3Cl has been studied and compared to earlier work on the reaction of F with CH3I. In this way, the influence of the leaving group on S N 2 reactions has been determined to infer its importance also regarding the transition state geometry and orientation effects. Checking beam overlaps of several beams is vital for the scattering experiments, especially when focused lasers are used to influence the molecular beam. In this thesis, a quantitative in-depth analysis of the imaging properties of this mode is presented. The description of the imaging process with Taylor matrices is very insightful and it has been recently extended to VMI settings. Finally, the question of how CH symmetric stretch vibrational excitation affects the reaction of F withvorgelegt von Martin SteiEnth. u.a. 4 Veröff. d. Verf. aus den Jahren 2013 - 2015Innsbruck, Univ., Diss., 2015OeBB(VLID)79291

Stretching vibration is a spectator in nucleophilic substitution

How chemical reactions are influenced by reactant vibrational excitation is a long-standing question at the core of chemical reaction dynamics. In reactions of polyatomic molecules, where the Polanyi rules are not directly applicable, certain vibrational modes can act as spectators. In nucleophilic substitution reactions, CH stretching vibrations have been considered to be such spectators. While this picture has been challenged by some theoretical studies, experimental insight has been lacking. We show that the nucleophilic substitution reaction of F- with CH3I is minimally influenced by an excitation of the symmetric CH stretching vibration. This contrasts with the strong vibrational enhancement of the proton transfer reaction measured in parallel. The spectator behavior of the stretching mode is supported by both quasi-classical trajectory simulations and the Sudden Vector Projection model

Imaging Proton Transfer and Dihalide Formation Pathways in Reactions of F(-) + CH3I

Ion–molecule reactions of the type X– + CH3Y are commonly assumed to produce Y– through bimolecular nucleophilic substitution (SN2). Beyond this reaction, additional reaction products have been observed throughout the last decades and have been ascribed to different entrance channel geometries differing from the commonly assumed collinear approach. We have performed a crossed beam velocity map imaging experiment on the F– + CH3I reaction at different relative collision energies between 0.4 and 2.9 eV. We find three additional channels competing with nucleophilic substitution at high energies. Experimental branching ratios and angle- and energy differential cross sections are presented for each product channel. The proton transfer product CH2I– is the main reaction channel, which competes with nucleophilic substitution up to 2.9 eV relative collision energy. At this level, the second additional channel, the formation of IF– via halogen abstraction, becomes more efficient. In addition, we present the first evidence for an [FHI]− product ion. This [FHI]− product ion is present only for a narrow range of collision energies, indicating possible dissociation at high energies. All three products show a similar trend with respect to their velocity- and scattering angle distributions, with isotropic scattering and forward scattering of the product ions occurring at low and high energies, respectively. Reactions leading to all three reaction channels present a considerable amount of energy partitioning in product internal excitation. The internally excited fraction shows a collision energy dependence only for CH2I–. A similar trend is observed for the isoelectronic OH– + CH3I system. The comparison of our experimental data at 1.55 eV collision energy with a recent theoretical calculation for the same system shows a slightly higher fraction of internal excitation than predicted, which is, however, compatible within the experimental accuracy

Imaging Proton Transfer and Dihalide Formation Pathways in Reactions of F –

[Image: see text] Ion–molecule reactions of the type X(–) + CH(3)Y are commonly assumed to produce Y(–) through bimolecular nucleophilic substitution (S(N)2). Beyond this reaction, additional reaction products have been observed throughout the last decades and have been ascribed to different entrance channel geometries differing from the commonly assumed collinear approach. We have performed a crossed beam velocity map imaging experiment on the F(–) + CH(3)I reaction at different relative collision energies between 0.4 and 2.9 eV. We find three additional channels competing with nucleophilic substitution at high energies. Experimental branching ratios and angle- and energy differential cross sections are presented for each product channel. The proton transfer product CH(2)I(–) is the main reaction channel, which competes with nucleophilic substitution up to 2.9 eV relative collision energy. At this level, the second additional channel, the formation of IF(–) via halogen abstraction, becomes more efficient. In addition, we present the first evidence for an [FHI](−) product ion. This [FHI](−) product ion is present only for a narrow range of collision energies, indicating possible dissociation at high energies. All three products show a similar trend with respect to their velocity- and scattering angle distributions, with isotropic scattering and forward scattering of the product ions occurring at low and high energies, respectively. Reactions leading to all three reaction channels present a considerable amount of energy partitioning in product internal excitation. The internally excited fraction shows a collision energy dependence only for CH(2)I(–). A similar trend is observed for the isoelectronic OH(–) + CH(3)I system. The comparison of our experimental data at 1.55 eV collision energy with a recent theoretical calculation for the same system shows a slightly higher fraction of internal excitation than predicted, which is, however, compatible within the experimental accuracy

Atomistic dynamics of elimination and nucleophilic substitution disentangled for the F- + CH3CH2Cl reaction

Chemical reaction dynamics are studied to monitor and understand the concerted motion of several atoms while they rearrange from reactants to products. When the number of atoms involved increases, the number of pathways, transition states and product channels also increases and rapidly presents a challenge to experiment and theory. Here we disentangle the dynamics of the competition between bimolecular nucleophilic substitution (S(N)2) and base-induced elimination (E2) in the polyatomic reaction F- + CH3CH2Cl. We find quantitative agreement for the energy- and angle-differential reactive scattering cross-sections between ion-imaging experiments and quasi-classical trajectory simulations on a 21-dimensional potential energy hypersurface. The anti-E2 pathway is most important, but the S(N)2 pathway becomes more relevant as the collision energy is increased. In both cases the reaction is dominated by direct dynamics. Our study presents atomic-level dynamics of a major benchmark reaction in physical organic chemistry, thereby pushing the number of atoms for detailed reaction dynamics studies to a size that allows applications in many areas of complex chemical networks and environments.As the number of atoms involved in a reaction increases, so do the experimental and theoretical challenges faced when studying their dynamics. Now, using ion-imaging experiments and quasi-classical trajectory simulations, the dynamics of the polyatomic reaction F- + CH3CH2Cl have been studied and the competition between bimolecular nucleophilic substitution and base-induced elimination has been disentangled

Cross sections for energetic heavy-ion impact on protonated water clusters

Energetic impact of multiple ionized oxygen on protonated water clusters in the range of eight to twenty-one water molecules is investigated on the ZERNIKE-LEIF facility. The target water clusters are stored in a Paul trap and thermalized by cold buffer gas. This well-controlled approach allows for a direct measurement of the total inelastic cross section leading to trap-loss processes of the target ions

Influence of the leaving group on the dynamics of a gas-phase SN2 reaction

In addition to nucleophile and solvent, the leaving group has a significant influence on nucleophilic substitution (SN2) reactions. Its role is frequently discussed with respect to reactivity, but its influence on the reaction dynamics remains obscured. Here, we uncover the influence of the leaving group on the gas phase dynamics of SN2 reactions in a combined approach of crossed-beam imaging and dynamics simulations. We have studied the reaction F- + CH3Cl and compared it to F- + CH3I. For the two leaving groups Cl and I we find very similar structures and energetics, but the dynamics show qualitatively different features. Simple scaling of the leaving group mass does not explain these differences. Instead, the relevant impact parameters for the reaction mechanisms are found to be crucial, which is attributed to the relative orientation of the approaching reactants. This effect occurs on short time scales and may also prevail under solution phase conditions

Proteometabolomics of initial and recurrent glioblastoma highlights an increased immune cell signature with altered lipid metabolism

International audienceAbstract Background There is an urgent need to better understand the mechanisms associated with the development, progression, and onset of recurrence after initial surgery in glioblastoma (GBM). The use of integrative phenotype-focused -omics technologies such as proteomics and lipidomics provides an unbiased approach to explore the molecular evolution of the tumor and its associated environment. Methods We assembled a cohort of patient-matched initial (iGBM) and recurrent (rGBM) specimens of resected GBM. Proteome and metabolome composition were determined by mass spectrometry-based techniques. We performed neutrophil-GBM cell coculture experiments to evaluate the behavior of rGBM-enriched proteins in the tumor microenvironment. ELISA-based quantitation of candidate proteins was performed to test the association of their plasma concentrations in iGBM with the onset of recurrence. Results Proteomic profiles reflect increased immune cell infiltration and extracellular matrix reorganization in rGBM. ASAH1, SYMN, and GPNMB were highly enriched proteins in rGBM. Lipidomics indicates the downregulation of ceramides in rGBM. Cell analyses suggest a role for ASAH1 in neutrophils and its localization in extracellular traps. Plasma concentrations of ASAH1 and SYNM show an association with time to recurrence. Conclusions We describe the potential importance of ASAH1 in tumor progression and development of rGBM via metabolic rearrangement and showcase the feedback from the tumor microenvironment to plasma proteome profiles. We report the potential of ASAH1 and SYNM as plasma markers of rGBM progression. The published datasets can be considered as a resource for further functional and biomarker studies involving additional -omics technologies