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Bull JN, Scholz MS, Carrascosa E, Kristiansson MK, Eklund G, Punnakayathil N, de Ruette N, Zettergren H, Schmidt HT, Cederquist H, Stockett MH. Ultraslow radiative cooling of Cn− (n = 3–5). J Chem Phys 2019; 151:114304. [DOI: 10.1063/1.5114678] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Kjaer C, Lissau H, Gravesen Salinas NK, Østergaard Madsen A, Stockett MH, Storm FE, Holm Hansen T, Andersen JU, Laursen BW, Mikkelsen KV, Brøndsted Nielsen M, Brøndsted Nielsen S. Luminescence Spectroscopy of Rhodamine Homodimer Dications in Vacuo
Reveals Strong Dye-Dye Interactions. Chemphyschem 2019; 20:533-537. [DOI: 10.1002/cphc.201800933] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2018] [Revised: 12/04/2018] [Indexed: 11/06/2022]
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Stockett MH, Björkhage M, Cederquist H, Schmidt HT, Zettergren H. Storage time dependent photodissociation action spectroscopy of polycyclic aromatic hydrocarbon cations in the cryogenic electrostatic storage ring DESIREE. Faraday Discuss 2019; 217:126-137. [DOI: 10.1039/c8fd00161h] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The intrinsic absorption profile and radiative cooling rate of coronene cations are reported.
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Bull JN, Buntine JT, Scholz MS, Carrascosa E, Giacomozzi L, Stockett MH, Bieske EJ. Photodetachment and photoreactions of substituted naphthalene anions in a tandem ion mobility spectrometer. Faraday Discuss 2019; 217:34-46. [DOI: 10.1039/c8fd00217g] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Tandem IMS-laser-IMS is used to probe the intrinsic electronic absorptions of deprotonated substituted naphthalene anions.
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de Ruette N, Dochain A, Launoy T, Nascimento RF, Kaminska M, Stockett MH, Vaeck N, Schmidt HT, Cederquist H, Urbain X. Mutual Neutralization of O^{-} with O^{+} and N^{+} at Subthermal Collision Energies. PHYSICAL REVIEW LETTERS 2018; 121:083401. [PMID: 30192576 DOI: 10.1103/physrevlett.121.083401] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2018] [Indexed: 06/08/2023]
Abstract
We have measured total absolute cross sections for the mutual neutralization (MN) of O^{-} with O^{+} and N^{+}. A fine resolution (of about 50 meV) in the kinetic energy spectra of the product neutral atoms allows unique identification of the atomic states participating in the mutual neutralization process. Cross sections and branching ratios have also been calculated down to 1 meV center-of-mass collision energy for these two systems, with a multichannel Landau-Zener model and an asymptotic method for the ionic-covalent coupling matrix elements. The importance of two-electron processes in one-electron transfer is demonstrated by the dominant contribution of a core-excited configuration of the nitrogen atom in N^{+}+O^{-} collisions. This effect is partially accounted for by introducing configuration mixing in the evaluation of coupling matrix elements.
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Bull JN, Carrascosa E, Giacomozzi L, Bieske EJ, Stockett MH. Ion mobility action spectroscopy of flavin dianions reveals deprotomer-dependent photochemistry. Phys Chem Chem Phys 2018; 20:19672-19681. [PMID: 30014081 PMCID: PMC6063075 DOI: 10.1039/c8cp03244k] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Photo-induced proton transfer, deprotomer-dependent photochemistry, and intramolecular charge transfer in flavin anions are investigated using action spectroscopy.
The intrinsic optical properties and photochemistry of flavin adenine dinucleotide (FAD) dianions are investigated using a combination of tandem ion mobility spectrometry and action spectroscopy. Two principal isomers are observed, the more stable form being deprotonated on the isoalloxazine group and a phosphate (N-3,PO4 deprotomer), and the other on the two phosphates (PO4,PO4 deprotomer). Ion mobility data and electronic action spectra suggest that photo-induced proton transfer occurs from the isoalloxazine group to a phosphate group, converting the PO4,PO4 deprotomer to the N-3,PO4 deprotomer. Comparisons of the isomer selective action spectra of FAD dianions and flavin monoanions with solution spectra and gas-phase photodissociation action spectra suggests that solvation shifts the electronic absorption of the deprotonated isoalloxazine group to higher energy. This is interpreted as evidence for significant charge transfer in the lowest optical transition of deprotonated isoalloxazine. Overall, this work demonstrates that the site of deprotonation of flavin anions strongly affects their electronic absorptions and photochemistry.
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Giacomozzi L, Kjær C, Langeland Knudsen J, Andersen LH, Brøndsted Nielsen S, Stockett MH. Absorption and luminescence spectroscopy of mass-selected flavin adenine dinucleotide mono-anions. J Chem Phys 2018; 148:214309. [PMID: 29884035 DOI: 10.1063/1.5024028] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
We report the absorption profile of isolated Flavin Adenine Dinucleotide (FAD) mono-anions recorded using photo-induced dissociation action spectroscopy. In this charge state, one of the phosphoric acid groups is deprotonated and the chromophore itself is in its neutral oxidized state. These measurements cover the first four optical transitions of FAD with excitation energies from 2.3 to 6.0 eV (210-550 nm). The S0 → S2 transition is strongly blue shifted relative to aqueous solution, supporting the view that this transition has a significant charge-transfer character. The remaining bands are close to their solution-phase positions. This confirms that the large discrepancy between quantum chemical calculations of vertical transition energies and solution-phase band maxima cannot be explained by solvent effects. We also report the luminescence spectrum of FAD mono-anions in vacuo. The gas-phase Stokes shift for S1 is 3000 cm-1, which is considerably larger than any previously reported for other molecular ions and consistent with a significant displacement of the ground and excited state potential energy surfaces. Consideration of the vibronic structure is thus essential for simulating the absorption and luminescence spectra of flavins.
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de Ruette N, Wolf M, Giacomozzi L, Alexander JD, Gatchell M, Stockett MH, Haag N, Zettergren H, Schmidt HT, Cederquist H. DESIREE electrospray ion source test bench and setup for collision induced dissociation experiments. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2018; 89:075102. [PMID: 30068131 DOI: 10.1063/1.5030528] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
In this paper, we give a detailed description of an electrospray ion source test bench and a single-pass setup for ion fragmentation studies at the Double ElectroStatic Ion Ring ExpEriment infrastructure at Stockholm University. This arrangement allows for collision-induced dissociation experiments at the center-of-mass energies between 10 eV and 1 keV. Charged fragments are analyzed with respect to their kinetic energies (masses) by means of an electrostatic energy analyzer with a wide angular acceptance and adjustable energy resolution.
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Chartkunchand KC, Stockett MH, Anderson EK, Eklund G, Kristiansson MK, Kamińska M, de Ruette N, Blom M, Björkhage M, Källberg A, Löfgren P, Reinhed P, Rosén S, Simonsson A, Zettergren H, Schmidt HT, Cederquist H. Dianion diagnostics in DESIREE: High-sensitivity detection of C n2- from a sputter ion source. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2018; 89:033112. [PMID: 29604753 DOI: 10.1063/1.5010077] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
A sputter ion source with a solid graphite target has been used to produce dianions with a focus on carbon cluster dianions, Cn2-, with n = 7-24. Singly and doubly charged anions from the source were accelerated together to kinetic energies of 10 keV per atomic unit of charge and injected into one of the cryogenic (13 K) ion-beam storage rings of the Double ElectroStatic Ion Ring Experiment facility at Stockholm University. Spontaneous decay of internally hot Cn2- dianions injected into the ring yielded Cn- anions with kinetic energies of 20 keV, which were counted with a microchannel plate detector. Mass spectra produced by scanning the magnetic field of a 90° analyzing magnet on the ion injection line reflect the production of internally hot C72- - C242- dianions with lifetimes in the range of tens of microseconds to milliseconds. In spite of the high sensitivity of this method, no conclusive evidence of C62- was found while there was a clear C72- signal with the expected isotopic distribution. This is consistent with earlier experimental studies and with theoretical predictions. An upper limit is deduced for a C62- signal that is two orders-of-magnitude smaller than that for C72-. In addition, CnO2- and CnCu2- dianions were detected.
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Stockett MH. Photo-induced proton-coupled electron transfer and dissociation of isolated flavin adenine dinucleotide mono-anions. Phys Chem Chem Phys 2018; 19:25829-25833. [PMID: 28745349 DOI: 10.1039/c7cp04068g] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The intrinsic optical absorption spectrum and photo-dissociation pathways of flavin adenine dinucleotide (FAD) mono-anions isolated in vacuo are probed using photo-induced dissociation (PID) action spectroscopy. The main photo-products are lumichrome and formylmethylflavin. Evidence is presented that the dissociation pathway leading to these products is non-statistical i.e. occurs during the excited state lifetime. This suggests that the stacking of the adenine and alloxazine chromophores, which enables ultra-fast quenching of the flavin excited state by photo-induced electron transfer in aqueous solution, is inhibited in vacuo. These results provide firm experimental confirmation that lumichrome formation from flavins proceeds via photo-induced, intra-molecular proton-coupled electron transfer.
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Stockett MH, Boesen M, Houmøller J, Brøndsted Nielsen S. Frontispiece: Accessing the Intrinsic Nature of Electronic Transitions from Gas‐Phase Spectroscopy of Molecular Ion/Zwitterion Complexes. Angew Chem Int Ed Engl 2017. [DOI: 10.1002/anie.201781361] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Stockett MH, Boesen M, Houmøller J, Brøndsted Nielsen S. Frontispiz: Accessing the Intrinsic Nature of Electronic Transitions from Gas‐Phase Spectroscopy of Molecular Ion/Zwitterion Complexes. Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201781361] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Stockett MH, Boesen M, Houmøller J, Brøndsted Nielsen S. Accessing the Intrinsic Nature of Electronic Transitions from Gas‐Phase Spectroscopy of Molecular Ion/Zwitterion Complexes. Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201611320] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Stockett MH, Boesen M, Houmøller J, Brøndsted Nielsen S. Accessing the Intrinsic Nature of Electronic Transitions from Gas‐Phase Spectroscopy of Molecular Ion/Zwitterion Complexes. Angew Chem Int Ed Engl 2017; 56:3490-3495. [DOI: 10.1002/anie.201611320] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2016] [Indexed: 11/07/2022]
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Stockett MH, Kjær C, Linder MK, Detty MR, Nielsen SB. Luminescence spectroscopy of chalcogen substituted rhodamine cations in vacuo. Photochem Photobiol Sci 2017; 16:779-784. [DOI: 10.1039/c7pp00049a] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
A library of fluorescent rhodamine cations has been characterized with view to their potential use in gas-phase structural biology experiments.
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Kjær C, Brøndsted Nielsen S, Stockett MH. Sibling rivalry: intrinsic luminescence from two xanthene dye monoanions, resorufin and fluorescein, provides evidence for excited-state proton transfer in the latter. Phys Chem Chem Phys 2017; 19:24440-24444. [DOI: 10.1039/c7cp04689h] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Excited-state proton transfer in gas-phase fluorescein monoanions results in a broad, featureless emission band and a large Stokes shift compared to resorufin, which shares the same xanthene core structure.
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Kjær C, Stockett MH, Pedersen BM, Nielsen SB. Strong Impact of an Axial Ligand on the Absorption by Chlorophyll a and b Pigments Determined by Gas-Phase Ion Spectroscopy Experiments. J Phys Chem B 2016; 120:12105-12110. [PMID: 27933942 DOI: 10.1021/acs.jpcb.6b10547] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The microenvironments in photosynthetic proteins affect the absorption by chlorophyll (Chl) pigments. It is, however, a challenge to disentangle the impact on the transition energies of different perturbations, for example, the global electrostatics of the protein (nonbonded environmental effects), exciton coupling between Chl's, conformational variations, and binding of an axial ligand to the magnesium center. This is needed to distinguish between the two most commonly proposed mechanisms for energy transport in photosynthetic proteins, relying on either weakly or strongly coupled pigments. Here, on the basis of photodissociation action spectroscopy, we establish that the redshift of the Soret absorption band due to binding of a negatively charged carboxylate (as present in aspartic acid and glutamic acid residues) is 0.1-0.2 eV for Chl a and b. This effect is almost enough to reproduce the well-known green color of plants and can account for the strong spectral variation between Chl's. The experimental data serve to benchmark future high-level calculations of excited-state energies. Finally, we demonstrate that complexes between Chl a and histidine, tagged by a quaternary ammonium ion, can be made in the gas phase by electrospray ionization, but more work is needed to produce enough ions for gas-phase spectroscopy.
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Stockett MH, Houmøller J, Støchkel K, Svendsen A, Brøndsted Nielsen S. A cylindrical quadrupole ion trap in combination with an electrospray ion source for gas-phase luminescence and absorption spectroscopy. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2016; 87:053103. [PMID: 27250388 DOI: 10.1063/1.4948316] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
A relatively simple setup for collection and detection of light emitted from isolated photo-excited molecular ions has been constructed. It benefits from a high collection efficiency of photons, which is accomplished by using a cylindrical ion trap where one end-cap electrode is a mesh grid combined with an aspheric condenser lens. The geometry permits nearly 10% of the emitted light to be collected and, after transmission losses, approximately 5% to be delivered to the entrance of a grating spectrometer equipped with a detector array. The high collection efficiency enables the use of pulsed tunable lasers with low repetition rates (e.g., 20 Hz) instead of continuous wave (cw) lasers or very high repetition rate (e.g., MHz) lasers that are typically used as light sources for gas-phase fluorescence experiments on molecular ions. A hole has been drilled in the cylinder electrode so that a light pulse can interact with the ion cloud in the center of the trap. Simulations indicate that these modifications to the trap do not significantly affect the storage capability and the overall shape of the ion cloud. The overlap between the ion cloud and the laser light is basically 100%, and experimentally >50% of negatively charged chromophore ions are routinely photodepleted. The performance of the setup is illustrated based on fluorescence spectra of several laser dyes, and the quality of these spectra is comparable to those reported by other groups. Finally, by replacing the optical system with a channeltron detector, we demonstrate that the setup can also be used for gas-phase action spectroscopy where either depletion or fragmentation is monitored to provide an indirect measurement on the absorption spectrum of the ion.
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Andersen LH, Bochenkova AV, Houmøller J, Kiefer HV, Lattouf E, Stockett MH. A PYP chromophore acts as a 'photoacid' in an isolated hydrogen bonded complex. Phys Chem Chem Phys 2016; 18:9909-13. [PMID: 27009407 DOI: 10.1039/c6cp00433d] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The light-induced response of a neutral Photoactive Yellow Protein chromophore in a hydrogen-bonded complex with a proton acceptor has been studied by dual-detection action absorption spectroscopy and density functional theory. We show that the chromophore is a 'photoacid' and that ultrafast excited-state proton transfer might be operative in an isolated complex.
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Milne BF, Kjaer C, Houmøller J, Stockett MH, Toker Y, Rubio A, Nielsen SB. On the Exciton Coupling between Two Chlorophyll Pigments in the Absence of a Protein Environment: Intrinsic Effects Revealed by Theory and Experiment. Angew Chem Int Ed Engl 2016; 55:6248-51. [DOI: 10.1002/anie.201601979] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2016] [Indexed: 11/10/2022]
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Milne BF, Kjaer C, Houmøller J, Stockett MH, Toker Y, Rubio A, Nielsen SB. On the Exciton Coupling between Two Chlorophyll Pigments in the Absence of a Protein Environment: Intrinsic Effects Revealed by Theory and Experiment. Angew Chem Int Ed Engl 2016. [DOI: 10.1002/ange.201601979] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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47
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Stockett MH, Nielsen SB. Transition energies of benzoquinone anions are immune to symmetry breaking by a single water molecule. Phys Chem Chem Phys 2016; 18:6996-7000. [DOI: 10.1039/c5cp06095h] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Breaking the symmetry of the p-benzoquinone anion by a single water molecule has almost no effect on its transition energies.
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Stockett MH, Gatchell M, Chen T, de Ruette N, Giacomozzi L, Wolf M, Schmidt HT, Zettergren H, Cederquist H. Threshold energies for single-carbon knockout from polycyclic aromatic hydrocarbons. J Phys Chem Lett 2015; 6:4504-4509. [PMID: 26523738 DOI: 10.1021/acs.jpclett.5b02080] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We have measured absolute cross sections for ultrafast (femtosecond) single-carbon knockout from polycyclic aromatic hydrocarbon (PAH) cations as functions of He–PAH center-of-mass collision energy in the 10–200 eV range. Classical molecular dynamics (MD) simulations cover this range and extend up to 105 eV. The shapes of the knockout cross sections are well-described by a simple analytical expression yielding experimental and MD threshold energies of EthExp = 32.5 ± 0.4 eV and EthMD = 41.0 ± 0.3 eV, respectively. These are the first measurements of knockout threshold energies for molecules isolated in vacuo. We further deduce semiempirical (SE) and MD displacement energies, i.e., the energy transfers to the PAH molecules at the threshold energies for knockout, of TdispSE = 23.3 ± 0.3 eV and TdispMD = 27.0 ± 0.3 eV. The semiempirical results compare favorably with measured displacement energies for graphene (Tdisp = 23.6 eV).
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Chen T, Gatchell M, Stockett MH, Delaunay R, Domaracka A, Micelotta ER, Tielens AGGM, Rousseau P, Adoui L, Huber BA, Schmidt HT, Cederquist H, Zettergren H. Formation of H2 from internally heated polycyclic aromatic hydrocarbons: excitation energy dependence. J Chem Phys 2015; 142:144305. [PMID: 25877576 DOI: 10.1063/1.4917021] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
We have investigated the effectiveness of molecular hydrogen (H2) formation from Polycyclic Aromatic Hydrocarbons (PAHs) which are internally heated by collisions with keV ions. The present and earlier experimental results are analyzed in view of molecular structure calculations and a simple collision model. We estimate that H2 formation becomes important for internal PAH temperatures exceeding about 2200 K, regardless of the PAH size and the excitation agent. This suggests that keV ions may effectively induce such reactions, while they are unlikely due to, e.g., absorption of single photons with energies below the Lyman limit. The present analysis also suggests that H2 emission is correlated with multi-fragmentation processes, which means that the [PAH-2H](+) peak intensities in the mass spectra may not be used for estimating H2-formation rates.
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Stockett MH, Brøndsted Nielsen S. Communication: Does a single CH3CN molecule attached to Ru(bipy)3(2+) affect its absorption spectrum? J Chem Phys 2015; 142:171102. [PMID: 25956080 DOI: 10.1063/1.4919781] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Tris(bipyridine)ruthenium(II) (Ru(bipy)3 (2+)) is a prototypical transition metal coordination complex whose photophysical properties have attracted considerable attention. A much debated issue is whether the metal-to-ligand charge transfer (MLCT) transition that accounts for the complex's beautiful red color is fully delocalized across all three bipyridine ligands or located on just one ligand. Here, we show based on gas-phase action spectroscopy that attachment of a single acetonitrile molecule does not change the absorption spectrum from that of the bare ions, which is indicative of a delocalized state. However, the gas-phase spectra of the bare and one solvent molecule complexes are significantly blueshifted relative to that obtained in bulk acetonitrile, which suggests that in solution the polarizability of many solvent molecules working together can localize the MLCT state. Our data clearly show that more than one solvent molecule is needed to break the symmetry of the MLCT excited state and reproduce its solution-phase characteristics.
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