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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 -