TY - JOUR A1 - Fischer, Kathrin H. A1 - Hemberger, Patrick A1 - Bodi, Andras A1 - Fischer, Ingo T1 - Photoionisation of the tropyl radical JF - Beilstein Journal of Organic Chemistry N2 - We present a study on the photoionisation of the cycloheptatrienyl (tropyl) radical, \(C_7H_7\), using tunable vacuum ultraviolet synchrotron radiation. Tropyl is generated by flash pyrolysis from bitropyl. Ions and electrons are detected in coincidence, permitting us to record mass-selected photoelectron spectra. The threshold photoelectron spectrum of tropyl, corresponding to the \(X^{+1}A1’ ← X^2E_2”\) transition, reveals an ionisation energy of 6.23 ± 0.02 eV, in good agreement with Rydberg extrapolations, but slightly lower than the value derived from earlier photoelectron spectra. Several vibrations can be resolved and are reassigned to the C–C stretch mode \(ν_{16}^+\) and to a combination of \(ν_{16}^+\) with the ring breathing mode \(ν_2^+\). Above 10.55 eV dissociative photoionisation of tropyl is observed, leading to the formation of \(C_5H_5^+\) and \(C_2H_2\). KW - threshold photoelectron spectroscopy KW - gas phase KW - dissociative photoionisation KW - reactive intermediates KW - synchrotron radiation Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-128652 VL - 9 ER - TY - INPR A1 - Röder, Anja A1 - Petersen, Jens A1 - Issler, Kevin A1 - Fischer, Ingo A1 - Mitric, Roland A1 - Poisson, Lionel T1 - Exploring the Excited-State Dynamics of Hydrocarbon Radicals, Biradicals and Carbenes using Time-Resolved Photoelectron Spectroscopy and Field-Induced Surface Hopping Simulations T2 - The Journal of Physical Chemistry A N2 - Reactive hydrocarbon molecules like radicals, biradicals and carbenes are not only key players in combustion processes and interstellar and atmospheric chemistry, but some of them are also important intermediates in organic synthesis. These systems typically possess many low-lying, strongly coupled electronic states. After light absorption, this leads to rich photodynamics characterized by a complex interplay of nuclear and electronic motion, which is still not comprehensively understood and not easy to investigate both experimentally and theoretically. In order to elucidate trends and contribute to a more general understanding, we here review our recent work on excited-state dynamics of open-shell hydrocarbon species using time-resolved photoelectron spectroscopy and field-induced surface hopping simulations, and report new results on the excited-state dynamics of the tropyl and the 1-methylallyl radical. The different dynamics are compared, and the difficulties and future directions of time-resolved photoelectron spectroscopy and excited state dynamics simulations of open-shell hydrocarbon molecules are discussed. KW - Excited state dynamics KW - Hydrocarbon radicals KW - time-resolved photoelectron spectroscopy KW - field-induced surface hopping Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-198734 UR - https://doi.org/10.1021/acs.jpca.9b06346 N1 - This document is the unedited Author’s version of a Submitted Work that was subsequently accepted for publication in Journal of Physical Chemistry A, copyright © American Chemical Society after peer review. To access the final edited and published work see Journal of Physical Chemistry A 2019, 123, 50, 10643-10662. https://doi.org/10.1021/acs.jpca.9b06346. ER - TY - INPR A1 - Hoche, Joscha A1 - Schmitt, Hans-Christian A1 - Humeniuk, Alexander A1 - Fischer, Ingo A1 - Mitrić, Roland A1 - Röhr, Merle I. S. T1 - The mechanism of excimer formation: an experimental and theoretical study on the pyrene dimer T2 - Physical Chemistry Chemical Physics N2 - The understanding of excimer formation in organic materials is of fundamental importance, since excimers profoundly influence their functional performance in applications such as light-harvesting, photovoltaics or organic electronics. We present a joint experimental and theoretical study of the ultrafast dynamics of excimer formation in the pyrene dimer in a supersonic jet, which is the archetype of an excimer forming system. We perform simulations of the nonadiabatic photodynamics in the frame of TDDFT that reveal two distinct excimer formation pathways in the gas-phase dimer. The first pathway involves local excited state relaxation close to the initial Franck–Condon geometry that is characterized by a strong excitation of the stacking coordinate exhibiting damped oscillations with a period of 350 fs that persist for several picoseconds. The second excimer forming pathway involves large amplitude oscillations along the parallel shift coordinate with a period of ≈900 fs that after intramolecular vibrational energy redistribution leads to the formation of a perfectly stacked dimer. The electronic relaxation within the excitonic manifold is mediated by the presence of intermolecular conical intersections formed between fully delocalized excitonic states. Such conical intersections may generally arise in stacked π-conjugated aggregates due to the interplay between the long-range and short-range electronic coupling. The simulations are supported by picosecond photoionization experiments in a supersonic jet that provide a time-constant for the excimer formation of around 6–7 ps, in good agreement with theory. Finally, in order to explore how the crystal environment influences the excimer formation dynamics we perform large scale QM/MM nonadiabatic dynamics simulations on a pyrene crystal in the framework of the long-range corrected tight-binding TDDFT. In contrast to the isolated dimer, the excimer formation in the crystal follows a single reaction pathway in which the initially excited parallel slip motion is strongly damped by the interaction with the surrounding molecules leading to the slow excimer stabilization on a picosecond time scale. KW - exciton dynamics KW - pyrene dimer Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-159656 UR - http://dx.doi.org/10.1039/C7CP03990E N1 - Submitted version ER - TY - JOUR A1 - Hoche, Joscha A1 - Schmitt, Hans-Christian A1 - Humeniuk, Alexander A1 - Fischer, Ingo A1 - Mitrić, Roland A1 - Röhr, Merle I. S. T1 - The mechanism of excimer formation: an experimental and theoretical study on the pyrene dimer JF - Physical Chemistry Chemical Physics N2 - The understanding of excimer formation in organic materials is of fundamental importance, since excimers profoundly influence their functional performance in applications such as light-harvesting, photovoltaics or organic electronics. We present a joint experimental and theoretical study of the ultrafast dynamics of excimer formation in the pyrene dimer in a supersonic jet, which is the archetype of an excimer forming system. We perform simulations of the nonadiabatic photodynamics in the frame of TDDFT that reveal two distinct excimer formation pathways in the gas-phase dimer. The first pathway involves local excited state relaxation close to the initial Franck–Condon geometry that is characterized by a strong excitation of the stacking coordinate exhibiting damped oscillations with a period of 350 fs that persist for several picoseconds. The second excimer forming pathway involves large amplitude oscillations along the parallel shift coordinate with a period of ≈900 fs that after intramolecular vibrational energy redistribution leads to the formation of a perfectly stacked dimer. The electronic relaxation within the excitonic manifold is mediated by the presence of intermolecular conical intersections formed between fully delocalized excitonic states. Such conical intersections may generally arise in stacked π-conjugated aggregates due to the interplay between the long-range and short-range electronic coupling. The simulations are supported by picosecond photoionization experiments in a supersonic jet that provide a time-constant for the excimer formation of around 6–7 ps, in good agreement with theory. Finally, in order to explore how the crystal environment influences the excimer formation dynamics we perform large scale QM/MM nonadiabatic dynamics simulations on a pyrene crystal in the framework of the long-range corrected tight-binding TDDFT. In contrast to the isolated dimer, the excimer formation in the crystal follows a single reaction pathway in which the initially excited parallel slip motion is strongly damped by the interaction with the surrounding molecules leading to the slow excimer stabilization on a picosecond time scale. KW - exciton dynamics KW - pyrene dimer Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-159514 UR - http://dx.doi.org/10.1039/C7CP03990E N1 - Accepted version VL - 19 IS - 36 ER - TY - INPR A1 - Röder, Anja A1 - Humeniuk, Alexander A1 - Giegerich, Jens A1 - Fischer, Ingo A1 - Poisson, Lionel A1 - Mitric, Roland T1 - Femtosecond Time-Resolved Photoelectron Spectroscopy of the Benzyl Radical T2 - Physical Chemistry Chemical Physics N2 - We present a joint experimental and computational study of the nonradiative deactivation of the benzyl radical, C\(_7\)H\(_7\) after UV excitation. Femtosecond time-resolved photoelectron imaging was applied to investigate the photodynamics of the radical. The experiments were accompanied by excited state dynamics simulations using surface hopping. Benzyl has been excited at 265 nm into the D-band (\(\pi\pi^*\)) and the dynamics was probed using probe wavelengths of 398 nm or 798 nm. With 398 nm probe a single time constant of around 70-80 fs was observed. When the dynamics was probed at 798 nm, a second time constant \(\tau_2\)=1.5 ps was visible. It is assigned to further non-radiative deactivation to the lower-lying D\(_1\)/D\(_2\) states. KW - Nonadiabatic dynamics KW - time-resolved photoelectron spectroscopy KW - benzyl radical Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-159474 UR - http://dx.doi.org/10.1039/C7CP01437F N1 - Submitted version ER - TY - JOUR A1 - Ramler, Jacqueline A1 - Poater, Jordi A1 - Hirsch, Florian A1 - Ritschel, Benedikt A1 - Fischer, Ingo A1 - Bickelhaupt, F. Matthias A1 - Lichtenberg, Crispin T1 - Carbon monoxide insertion at a heavy p-block element: unprecedented formation of a cationic bismuth carbamoyl JF - Chemical Science N2 - Major advances in the chemistry of 5th and 6th row heavy p-block element compounds have recently uncovered intriguing reactivity patterns towards small molecules such as H\(_2\), CO\(_2\), and ethylene. However, well-defined, homogeneous insertion reactions with carbon monoxide, one of the benchmark substrates in this field, have not been reported to date. We demonstrate here, that a cationic bismuth amide undergoes facile insertion of CO into the Bi–N bond under mild conditions. This approach grants direct access to the first cationic bismuth carbamoyl species. Its characterization by NMR, IR, and UV/vis spectroscopy, elemental analysis, single-crystal X-ray analysis, cyclic voltammetry, and DFT calculations revealed intriguing properties, such as a reversible electron transfer at the bismuth center and an absorption feature at 353 nm ascribed to a transition involving σ- and π-type orbitals of the bismuth-carbamoyl functionality. A combined experimental and theoretical approach provided insight into the mechanism of CO insertion. The substrate scope could be extended to isonitriles. KW - carbon monoxide KW - p-block element Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-181627 VL - 10 ER - TY - JOUR A1 - Ojha, Animesh K. A1 - Forster, Stefan A1 - Kumar, Sumeet A1 - Vats, Siddharth A1 - Negi, Segeeta A1 - Fischer, Ingo T1 - Synthesis of well-dispersed silver nanorods of different aspect ratios and their antimicrobial properties against gram positive and negative bacterial strains JF - Journal of Nanobiotechnology N2 - In the present contribution, we describe the synthesis of highly dispersed silver nanorods (NRs) of different aspect ratios using a chemical route. The shape and size of the synthesized NRs were characterized by Transmission Electron Microscopy (TEM) and UV-visible spectroscopy. Longitudinal and transverse absorptions bands confirm the rod type structure. The experimentally recorded UV-visible spectra of NRs solutions were fitted by using an expression of the extinction coefficient for rod like nano structures under the dipole approximation. Simulated and experimentally observed UV-visible spectra were compared to determine the aspect ratios (R) of NRs. The average values of R for NR1, NR2 and NR3 solutions are estimated to be 3.0 +/- 0.1, 1.8 +/- 0.1 and 1.2 +/- 0.1, respectively. These values are in good agreement with those obtained by TEM micrographs. The silver NRs of known aspect ratios are used to study antimicrobial activities against B. subtilis (gram positive) and E. coli (gram negative) microbes. We observed that the NRs of intermediate aspect ratio (R = 1.8) have greater antimicrobial effect against both, B. subtilis (gram positive) and E. coli (gram negative). The NRs of aspect ratio, R = 3.0 has better antimicrobial activities against gram positive than on the gram negative. KW - silver KW - nano rods KW - TEM KW - antimicrobial activities KW - nanowire formation KW - gold nanoparticles KW - Raman-scattering KW - nanostructures KW - particles Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-122837 SN - 1477-3155 VL - 11 IS - 42 ER - TY - JOUR A1 - Braunschweig, Holger A1 - Constantinidis, Philipp A1 - Dellermann, Theresa A1 - Ewing, William A1 - Fischer, Ingo A1 - Hess, Merlin A1 - Knight, Fergus A1 - Rempel, Anna A1 - Schneider, Christoph A1 - Ullrich, Stefan A1 - Vargas, Alfredo A1 - Woolins, Derek T1 - Highly Strained Heterocycles Constructed from Boron–Boron Multiple Bonds and Heavy Chalcogens JF - Angewandte Chemie, International Edition N2 - The reactions of a diborene with elemental selenium or tellurium are shown to afford a diboraselenirane or diboratellurirane, respectively. These reactions are reminiscent of the sequestration of subvalent oxygen and nitrogen in the formation of oxiranes and aziridines; however, such reactivity is not known between alkenes and the heavy chalcogens. Although carbon is too electronegative to affect the reduction of elements with lower relative electronegativity, the highly reducing nature of the B B double bond enables reactions with Se0 and Te0. The capacity of multiple bonds between boron atoms to donate electron density is highlighted in reactions where diborynes behave as nucleophiles, attacking one of the two Te atoms of diaryltellurides, forming salts consisting of diboratellurenium cations and aryltelluride anions. KW - Boron KW - Heterocycles KW - Multiple bonds KW - Selenium KW - Tellurium KW - Bor KW - Heterocyclische Verbindungen KW - Selen KW - Tellur Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-138237 N1 - This is the peer reviewed version of the following article: Angew. Chem. Int. Ed. 2016, 55, 5606–5609, which has been published in final form at 10.1002/anie.201601691. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. N1 - Accepted Version VL - 55 IS - 18 SP - 5606 EP - 5609 ER - TY - JOUR A1 - Ojha, Animesh K. A1 - Forster, Stefan A1 - Kumar, Sumeet A1 - Vats, Siddharth A1 - Negi, Sangeeta A1 - Fischer, Ingo T1 - Synthesis of well–dispersed silver nanorods of different aspect ratios and their antimicrobial properties against gram positive and negative bacterial strains JF - Journal of Nanobiotechnology N2 - In the present contribution, we describe the synthesis of highly dispersed silver nanorods (NRs) of different aspect ratios using a chemical route. The shape and size of the synthesized NRs were characterized by Transmission Electron Microscopy (TEM) and UV-visible spectroscopy. Longitudinal and transverse absorptions bands confirm the rod type structure. The experimentally recorded UV-visible spectra of NRs solutions were fitted by using an expression of the extinction coefficient for rod like nano structures under the dipole approximation. Simulated and experimentally observed UV-visible spectra were compared to determine the aspect ratios (R) of NRs. The average values of R for NR1, NR2 and NR3 solutions are estimated to be 3.0 ± 0.1, 1.8 ± 0.1 and 1.2 ± 0.1, respectively. These values are in good agreement with those obtained by TEM micrographs. The silver NRs of known aspect ratios are used to study antimicrobial activities against B. subtilis (gram positive) and E. coli (gram negative) microbes. We observed that the NRs of intermediate aspect ratio (R = 1.8) have greater antimicrobial effect against both, B. subtilis (gram positive) and E. coli (gram negative). The NRs of aspect ratio, R = 3.0 has better antimicrobial activities against gram positive than on the gram negative. KW - antimicrobial activities KW - silver KW - nano rods KW - TEM Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-132222 VL - 11 IS - 42 ER - TY - JOUR A1 - Hoche, Joscha A1 - Flock, Marco A1 - Miao, Xincheng A1 - Philipp, Luca Nils A1 - Wenzel, Michael A1 - Fischer, Ingo A1 - Mitric, Roland T1 - Excimer formation dynamics in the isolated tetracene dimer JF - Chemical Science N2 - The understanding of excimer formation and its interplay with the singlet-correlated triplet pair state \(^{1}\)(TT) is of high significance for the development of efficient organic electronics. Here, we study the photoinduced dynamics of the tetracene dimer in the gas phase by time-resolved photoionisation and photoion imaging experiments as well as nonadiabatic dynamics simulations in order to obtain mechanistic insight into the excimer formation dynamics. The experiments are performed using a picosecond laser system for excitation into the S\(_{2}\) state and reveal a biexponential time dependence. The time constants, obtained as a function of excess energy, lie in the range between ≈10 ps and 100 ps and are assigned to the relaxation of the excimer on the S\(_{1}\) surface and to its deactivation to the ground state. Simulations of the quantum-classical photodynamics are carried out in the frame of the semi-empirical CISD and TD-lc-DFTB methods. Both theoretical approaches reveal a dominating relaxation pathway that is characterised by the formation of a perfectly stacked excimer. TD-lc-DFTB simulations have also uncovered a second relaxation channel into a less stable dimer conformation in the S\(_{1}\) state. Both methods have consistently shown that the electronic and geometric relaxation to the excimer state is completed in less than 10 ps. The inclusion of doubly excited states in the CISD dynamics and their diabatisation further allowed to observe a transient population of the \(^{1}\)(TT) state, which, however, gets depopulated on a timescale of 8 ps, leading finally to the trapping in the excimer minimum. KW - excimer formation KW - tetracene dimer KW - organic electronics Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-251559 VL - 12 IS - 36 SP - 11965 EP - 11975 ER - TY - JOUR A1 - Mukhopadhyay, Deb Pratim A1 - Schleier, Domenik A1 - Wirsing, Sara A1 - Ramler, Jaqueline A1 - Kaiser, Dustin A1 - Reusch, Engelbert A1 - Hemberger, Patrick A1 - Preitschopf, Tobias A1 - Krummenacher, Ivo A1 - Engels, Bernd A1 - Fischer, Ingo A1 - Lichtenberg, Crispin T1 - Methylbismuth: an organometallic bismuthinidene biradical JF - Chemical Science N2 - We report the generation, spectroscopic characterization, and computational analysis of the first free (non-stabilized) organometallic bismuthinidene, BiMe. The title compound was generated in situ from BiMe\(_3\) by controlled homolytic Bi–C bond cleavage in the gas phase. Its electronic structure was characterized by a combination of photoion mass-selected threshold photoelectron spectroscopy and DFT as well as multi-reference computations. A triplet ground state was identified and an ionization energy (IE) of 7.88 eV was experimentally determined. Methyl abstraction from BiMe\(_3\) to give [BiMe(_2\)]• is a key step in the generation of BiMe. We reaveal a bond dissociation energy of 210 ± 7 kJ mol\(^{−1}\), which is substantially higher than the previously accepted value. Nevertheless, the homolytic cleavage of Me–BiMe\(_2\) bonds could be achieved at moderate temperatures (60–120 °C) in the condensed phase, suggesting that [BiMe\(_2\)]• and BiMe are accessible as reactive intermediates under these conditions. KW - methylbismuth KW - Photoelektronenspektroskopie Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-251657 UR - https://pubs.rsc.org/en/content/articlelanding/2020/SC/D0SC02410D VL - 11 IS - 29 ER - TY - JOUR A1 - Gerlach, Marius A1 - Monninger, Sophie A1 - Schleier, Domenik A1 - Hemberger, Patrick A1 - Goettel, James T. A1 - Braunschweig, Holger A1 - Fischer, Ingo T1 - Photoelectron Photoion Coincidence Spectroscopy of NCl\(_{3}\) and NCl\(_{2}\) JF - ChemPhysChem N2 - We investigate NCl\(_{3}\) and the NCl\(_{2}\) radical by photoelectron-photoion coincidence spectroscopy using synchrotron radiation. The mass selected threshold photoelectron spectrum (ms-TPES) of NCl\(_{3}\) is broad and unstructured due to the large geometry change. An ionization energy of 9.7±0.1 eV is estimated from the spectrum and supported by computations. NCl2 is generated by photolysis at 213 nm from NCl\(_{3}\) and its ms-TPES shows an extended vibrational progression with a 90 meV spacing that is assigned to the symmetric N−Cl stretching mode in the cation. An adiabatic ionization energy of 9.94 ± 0.02 eV is determined. KW - radicals KW - photoelectron spectroscopy KW - synchrotron radiation KW - nitrogen trichloride KW - photolysis Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-257322 VL - 22 IS - 21 ER - TY - JOUR A1 - Hahn, Lukas A1 - Beudert, Matthias A1 - Gutmann, Marcus A1 - Keßler, Larissa A1 - Stahlhut, Philipp A1 - Fischer, Lena A1 - Karakaya, Emine A1 - Lorson, Thomas A1 - Thievessen, Ingo A1 - Detsch, Rainer A1 - Lühmann, Tessa A1 - Luxenhofer, Robert T1 - From Thermogelling Hydrogels toward Functional Bioinks: Controlled Modification and Cytocompatible Crosslinking JF - Macromolecular Bioscience N2 - Hydrogels are key components in bioink formulations to ensure printability and stability in biofabrication. In this study, a well-known Diels-Alder two-step post-polymerization modification approach is introduced into thermogelling diblock copolymers, comprising poly(2-methyl-2-oxazoline) and thermoresponsive poly(2-n-propyl-2-oxazine). The diblock copolymers are partially hydrolyzed and subsequently modified by acid/amine coupling with furan and maleimide moieties. While the thermogelling and shear-thinning properties allow excellent printability, trigger-less cell-friendly Diels-Alder click-chemistry yields long-term shape-fidelity. The introduced platform enables easy incorporation of cell-binding moieties (RGD-peptide) for cellular interaction. The hydrogel is functionalized with RGD-peptides using thiol-maleimide chemistry and cell proliferation as well as morphology of fibroblasts seeded on top of the hydrogels confirm the cell adhesion facilitated by the peptides. Finally, bioink formulations are tested for biocompatibility by incorporating fibroblasts homogenously inside the polymer solution pre-printing. After the printing and crosslinking process good cytocompatibility is confirmed. The established bioink system combines a two-step approach by physical precursor gelation followed by an additional chemical stabilization, offering a broad versatility for further biomechanical adaptation or bioresponsive peptide modification. KW - chemical crosslinking KW - biofabrication KW - bioprinting KW - hydrogels Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-257542 VL - 21 IS - 10 ER - TY - JOUR A1 - Preitschopf, Tobias A1 - Sturm, Floriane A1 - Stroganova, Iuliia A1 - Lemmens, Alexander K. A1 - Rijs, Anouk M. A1 - Fischer, Ingo T1 - IR/UV Double Resonance Study of the 2‐Phenylallyl Radical and its Pyrolysis Products JF - Chemistry – A European Journal N2 - Isolated 2‐phenylallyl radicals (2‐PA), generated by pyrolysis from a nitrite precursor, have been investigated by IR/UV ion dip spectroscopy using free electron laser radiation. 2‐PA is a resonance‐stabilized radical that is considered to be involved in the formation of polycyclic aromatic hydrocarbons (PAH) in combustion, but also in interstellar space. The radical is identified based on its gas‐phase IR spectrum. Furthermore, a number of bimolecular reaction products are identified, showing that the self‐reaction as well as reactions with unimolecular decomposition products of 2‐PA form several PAH efficiently. Possible mechanisms are discussed and the chemistry of 2‐PA is compared with the one of the related 2‐methylallyl and phenylpropargyl radicals. KW - free electron laser KW - free jet KW - IR spectroscopy KW - PAH formation KW - radical reactions Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-312338 VL - 29 IS - 13 ER - TY - JOUR A1 - Schleier, Domenik A1 - Reusch, Engelbert A1 - Lummel, Lisa A1 - Hemberger, Patrick A1 - Fischer, Ingo T1 - Threshold photoelectron spectroscopy of IO and IOH JF - ChemPhysChem N2 - Iodine oxides appear as reactive intermediates in atmospheric chemistry. Here, we investigate IO and HOI by mass‐selective threshold photoelectron spectroscopy (ms‐TPES), using synchrotron radiation. IO and HOI are generated by photolyzing iodine in the presence of ozone. For both molecules, accurate ionization energies are determined, 9.71±0.02 eV for IO and 9.79±0.02 eV for HOI. The strong spin‐spin interaction in the 3Σ− ground state of IO+ leads to an energy splitting into the Ω=0 and Ω=±1 sublevels. Upon ionization, the I−O bond shortens significantly in both molecules; thus, a vibrational progression, assigned to the I−O stretch, is apparent in both spectra. KW - ionization potential KW - radicals KW - reactive intermediates KW - photolysis KW - synchrotron radiatoren Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-204751 VL - 20 IS - 19 ER - TY - JOUR A1 - Reusch, Engelbert A1 - Holzmeier, Fabian A1 - Gerlach, Marius A1 - Fischer, Ingo A1 - Hemberger, Patrick T1 - Decomposition of Picolyl Radicals at High Temperature: A Mass Selective Threshold Photoelectron Spectroscopy Study JF - Chemistry - A European Journal N2 - The reaction products of the picolyl radicals at high temperature were characterized by mass‐selective threshold photoelectron spectroscopy in the gas phase. Aminomethylpyridines were pyrolyzed to initially produce picolyl radicals (m /z =92). At higher temperatures further thermal reaction products are generated in the pyrolysis reactor. All compounds were identified by mass‐selected threshold photoelectron spectroscopy and several hitherto unexplored reactive molecules were characterized. The mechanism for several dissociation pathways was outlined in computations. The spectrum of m /z =91, resulting from hydrogen loss of picolyl, shows four isomers, two ethynyl pyrroles with adiabatic ionization energies (IE\(_{ad}\)) of 7.99 eV (2‐ethynyl‐1H ‐pyrrole) and 8.12 eV (3‐ethynyl‐1H ‐pyrrole), and two cyclopentadiene carbonitriles with IE′s of 9.14 eV (cyclopenta‐1,3‐diene‐1‐carbonitrile) and 9.25 eV (cyclopenta‐1,4‐diene‐1‐carbonitrile). A second consecutive hydrogen loss forms the cyanocyclopentadienyl radical with IE′s of 9.07 eV (T\(_0\)) and 9.21 eV (S\(_1\)). This compound dissociates further to acetylene and the cyanopropynyl radical (IE=9.35 eV). Furthermore, the cyclopentadienyl radical, penta‐1,3‐diyne, cyclopentadiene and propargyl were identified in the spectra. Computations indicate that dissociation of picolyl proceeds initially via a resonance‐stabilized seven‐membered ring. KW - ionization energy KW - photoelectron spectroscopy KW - pyrolysis KW - radicals KW - synchrotron radiation Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-208132 VL - 25 IS - 72 ER - TY - JOUR A1 - Hirsch, Florian A1 - Pachner, Kai A1 - Fischer, Ingo A1 - Issler, Kevin A1 - Petersen, Jens A1 - Mitric, Roland A1 - Bakels, Sjors A1 - Rijs, Anouk M. T1 - Do Xylylenes Isomerize in Pyrolysis? JF - ChemPhysChem N2 - We report infrared spectra of xylylene isomers in the gas phase, using free electron laser (FEL) radiation. All xylylenes were generated by flash pyrolysis. The IR spectra were obtained by monitoring the ion dip signal, using a IR/UV double resonance scheme. A gas phase IR spectrum of para‐xylylene  was recorded, whereas ortho‐ and meta‐xylylene were found to partially rearrange to benzocyclobutene and styrene. Computations of the UV oscillator strength  for all molecules were carried out and provde an explanation for the observation of the isomerization products. KW - biradicals KW - high-temperature chemistry KW - IR spectroscopy KW - pyrolysis KW - xylylene Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-218316 VL - 21 IS - 14 SP - 1515 EP - 1518 ER - TY - JOUR A1 - Schleier, Domenik A1 - Gerlach, Marius A1 - Pratim Mukhopadhyay, Deb A1 - Karaev, Emil A1 - Schaffner, Dorothee A1 - Hemberger, Patrick A1 - Fischer, Ingo T1 - Ammonia Borane, NH\(_{3}\)BH\(_{3}\): A Threshold Photoelectron-Photoion Coincidence Study of a Potential Hydrogen-Storage Material JF - Chemistry-A European Journal N2 - We have investigated the photoionization of ammonia borane (AB) and determined adiabatic ionization energy to be 9.26±0.03 eV for the X\(^{+}\) \(^{2}\)E←X \(^{1}\)A\(_{1}\) transition. Although the threshold photoelectron spectrum appears at first glance to be similar to the one of the isosteric ethane, the electronic situation differs markedly, due to different orbital energies. In addition, an appearance energy AE\(_{0K}\)-(NH\(_{3}\)BH\(_{3}\), NH\(_{3}\)BH\(_{2}\)\(^{+}\))= 10.00±0.03 eV has been determined, corresponding to the loss of a hydrogen atom at the BH\(_{3}\)-site. From the data, a 0 K bond dissociation energy for the B−H bond in the cation of 71.5±3 kJ mol\(^{-1}\) was derived, whereas the one in the neutral compound has been estimated to be 419±10 kJ mol\(^{-1}\). KW - ammonia borane KW - photoelectron spectroscopy KW - molecular orbitals KW - hydrogen storage KW - Jahn–Teller effect Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-318895 VL - 28 IS - 42 ER - TY - JOUR A1 - Ahmed, Bilal A1 - Ojha, Animesh K. A1 - Hirsch, Florian A1 - Fischer, Ingo A1 - Patrice, Donfack A1 - Materny, Arnulf T1 - Tailoring of enhanced interfacial polarization in WO\(_3\) nanorods grown over reduced graphene oxide synthesized by a one-step hydrothermal method JF - RSC Advances N2 - In the present report, well-defined WO3 nanorods (NRs) and a rGO–WO\(_3\) composite were successfully synthesized using a one-pot hydrothermal method. The crystal phase, structural morphology, shape, and size of the as-synthesized samples were studied using X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. The optical properties of the synthesized samples were investigated by Raman, ultraviolet-visible (UV-Vis) and photoluminescence (PL) spectroscopy. Raman spectroscopy and TEM results validate the formation of WO\(_3\) (NRs) on the rGO sheet. The value of the dielectric constant (ε′) of WO3 NRs and rGO–WO\(_3\) composite is decreased with an increase in frequency. At low frequency (2.5 to 3.5 Hz), the value of ε′ for the rGO–WO3 composite is greater than that of pure WO\(_3\) NRs. This could be due to the fact that the induced charges follow the ac signal. However, at higher frequency (3.4 to 6.0), the value of ε′ for the rGO–WO\(_3\) composite is less compared to that of the pure WO3 NRs. The overall decrease in the value of ε′ could be due to the occurrence of a polarization process at the interface of the rGO sheet and WO3 NRs. Enhanced interfacial polarization in the rGO–WO\(_3\) composite is observed, which may be attributed to the presence of polar functional groups on the rGO sheet. These functional groups trap charge carriers at the interface, resulting in an enhancement of the interfacial polarization. The value of the dielectric modulus is also calculated to further confirm this enhancement. The values of the ac conductivity of the WO\(_3\) NRs and rGO–WO\(_3\) composite were calculated as a function of the frequency. The greater value of the ac conductivity in the rGO–WO\(_3\) composite compared to that of the WO\(_3\) NRs confirms the restoration of the sp:\(^{++}\) network during the in situ synthesis of the rGO–WO\(_3\) composite, which is well supported by the results obtained by Raman spectroscopy. KW - chemistry Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-181829 VL - 7 IS - 23 ER -