@article{SchleierReuschLummeletal.2019, author = {Schleier, Domenik and Reusch, Engelbert and Lummel, Lisa and Hemberger, Patrick and Fischer, Ingo}, title = {Threshold photoelectron spectroscopy of IO and IOH}, series = {ChemPhysChem}, volume = {20}, journal = {ChemPhysChem}, number = {19}, doi = {10.1002/cphc.201900813}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-204751}, pages = {2413-2416}, year = {2019}, abstract = {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thus, a vibrational progression, assigned to the I-O stretch, is apparent in both spectra.}, language = {en} } @unpublished{HocheSchmittHumeniuketal.2017, author = {Hoche, Joscha and Schmitt, Hans-Christian and Humeniuk, Alexander and Fischer, Ingo and Mitrić, Roland and R{\"o}hr, Merle I. S.}, title = {The mechanism of excimer formation: an experimental and theoretical study on the pyrene dimer}, series = {Physical Chemistry Chemical Physics}, journal = {Physical Chemistry Chemical Physics}, doi = {10.1039/C7CP03990E}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-159656}, year = {2017}, abstract = {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.}, language = {en} } @article{HocheSchmittHumeniuketal.2017, author = {Hoche, Joscha and Schmitt, Hans-Christian and Humeniuk, Alexander and Fischer, Ingo and Mitrić, Roland and R{\"o}hr, Merle I. S.}, title = {The mechanism of excimer formation: an experimental and theoretical study on the pyrene dimer}, series = {Physical Chemistry Chemical Physics}, volume = {19}, journal = {Physical Chemistry Chemical Physics}, number = {36}, doi = {10.1039/C7CP03990E}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-159514}, pages = {25002-25015}, year = {2017}, abstract = {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.}, language = {en} } @article{AhmedOjhaHirschetal.2017, author = {Ahmed, Bilal and Ojha, Animesh K. and Hirsch, Florian and Fischer, Ingo and Patrice, Donfack and Materny, Arnulf}, title = {Tailoring of enhanced interfacial polarization in WO\(_3\) nanorods grown over reduced graphene oxide synthesized by a one-step hydrothermal method}, series = {RSC Advances}, volume = {7}, journal = {RSC Advances}, number = {23}, doi = {10.1039/c7ra00730b}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-181829}, pages = {13985-13996}, year = {2017}, abstract = {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.}, language = {en} } @article{OjhaForsterKumaretal.2013, author = {Ojha, Animesh K. and Forster, Stefan and Kumar, Sumeet and Vats, Siddharth and Negi, Sangeeta and Fischer, Ingo}, title = {Synthesis of well-dispersed silver nanorods of different aspect ratios and their antimicrobial properties against gram positive and negative bacterial strains}, series = {Journal of Nanobiotechnology}, volume = {11}, journal = {Journal of Nanobiotechnology}, number = {42}, doi = {10.1186/1477-3155-11-42}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-132222}, year = {2013}, abstract = {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.}, language = {en} } @article{OjhaForsterKumaretal.2013, author = {Ojha, Animesh K. and Forster, Stefan and Kumar, Sumeet and Vats, Siddharth and Negi, Segeeta and Fischer, Ingo}, title = {Synthesis of well-dispersed silver nanorods of different aspect ratios and their antimicrobial properties against gram positive and negative bacterial strains}, series = {Journal of Nanobiotechnology}, volume = {11}, journal = {Journal of Nanobiotechnology}, number = {42}, issn = {1477-3155}, doi = {10.1186/1477-3155-11-42}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-122837}, year = {2013}, abstract = {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.}, language = {en} } @article{FischerHembergerBodietal.2013, author = {Fischer, Kathrin H. and Hemberger, Patrick and Bodi, Andras and Fischer, Ingo}, title = {Photoionisation of the tropyl radical}, series = {Beilstein Journal of Organic Chemistry}, volume = {9}, journal = {Beilstein Journal of Organic Chemistry}, doi = {10.3762/bjoc.9.77}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-128652}, pages = {681-688}, year = {2013}, abstract = {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 \(C_2H_2\).}, language = {en} } @article{GerlachMonningerSchleieretal.2021, author = {Gerlach, Marius and Monninger, Sophie and Schleier, Domenik and Hemberger, Patrick and Goettel, James T. and Braunschweig, Holger and Fischer, Ingo}, title = {Photoelectron Photoion Coincidence Spectroscopy of NCl\(_{3}\) and NCl\(_{2}\)}, series = {ChemPhysChem}, volume = {22}, journal = {ChemPhysChem}, number = {21}, doi = {10.1002/cphc.202100537}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-257322}, pages = {2164-2167}, year = {2021}, abstract = {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.}, language = {en} } @article{MukhopadhyaySchleierWirsingetal.2020, author = {Mukhopadhyay, Deb Pratim and Schleier, Domenik and Wirsing, Sara and Ramler, Jaqueline and Kaiser, Dustin and Reusch, Engelbert and Hemberger, Patrick and Preitschopf, Tobias and Krummenacher, Ivo and Engels, Bernd and Fischer, Ingo and Lichtenberg, Crispin}, title = {Methylbismuth: an organometallic bismuthinidene biradical}, series = {Chemical Science}, volume = {11}, journal = {Chemical Science}, number = {29}, doi = {10.1039/D0SC02410D}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-251657}, pages = {7562-7568}, year = {2020}, abstract = {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.}, subject = {Photoelektronenspektroskopie}, language = {en} } @article{PreitschopfSturmStroganovaetal.2023, author = {Preitschopf, Tobias and Sturm, Floriane and Stroganova, Iuliia and Lemmens, Alexander K. and Rijs, Anouk M. and Fischer, Ingo}, title = {IR/UV Double Resonance Study of the 2-Phenylallyl Radical and its Pyrolysis Products}, series = {Chemistry - A European Journal}, volume = {29}, journal = {Chemistry - A European Journal}, number = {13}, doi = {10.1002/chem.202202943}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-312338}, year = {2023}, abstract = {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.}, language = {en} }