Journal: Physical Chemistry Chemical Physics

Abbreviation

Phys. Chem. Chem. Phys.

Publisher

Royal Society of Chemistry

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ISSN

1463-9084
1463-9076

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Publications1 - 10 of 436
  • Assessing relative humidity dependent photoacoustics to retrieve mass accommodation coefficients of single optically trapped aerosol particles
    Item type: Journal Article
    Diveky, Matus; Roy, Sandra; Cremer, Johannes; et al. (2019)
    Physical Chemistry Chemical Physics
    Photoacoustic spectroscopy is widely used to measure the light absorption of aerosols. However, the impact of key factors such as the effect of relative humidity and mass exchange on photoacoustic measurements are still poorly understood. We assess such measurement biases and their physical origin by analysing the photoacoustic signal of single tetraethylene glycol (TEG) particles at varying relative humidities. Our results show a decrease in the photoacoustic signal at elevated relative humidities for small particles (0.8–1.5 μm), while for larger sizes (2.2–3.2 μm) the trend is reversed. We model the photoacoustic signal to interpret the observed behaviour in terms of mass and heat flux contribution. The single particle photoacoustic signal analysis presented in this paper additionally allows for the retrieval of the mass accommodation coefficient. Fitting our experimental data to the theoretical model reveals values of αM ≈ 0.02–0.005 for water on TEG in the temperature range 295–309 K.
  • Trapping cold molecular hydrogen
    Item type: Journal Article
    Seiler, Christian; Hogan, Stephen D.; Merkt, Frédéric (2011)
    Physical Chemistry Chemical Physics
  • Quantifying proton NMR coherent linewidth in proteins under fast MAS conditions: a second moment approach
    Item type: Journal Article
    Malär, Alexander A.; Smith-Penzel, Susanne; Camenisch, Gian-Marco; et al. (2019)
    Physical Chemistry Chemical Physics
    Proton detected solid-state NMR under fast magic-angle-spinning (MAS) conditions is currently redefining the applications of solid-state NMR, in particular in structural biology. Understanding the contributions to the spectral linewidth is thereby of paramount importance. When disregarding the sample-dependent inhomogeneous contributions, the NMR proton linewidth is defined by homogeneous broadening, which has incoherent and coherent contributions. Understanding and disentangling these different contributions in multi-spin systems like proteins is still an open issue. The coherent contribution is mainly caused by the dipolar interaction under MAS and is determined by the molecular structure and the proton chemical shifts. Numerical simulation approaches based on numerically exact direct integration of the Liouville–von Neumann equation can give valuable information about the lineshape, but are limited to small spin systems (<12 spins). We present an alternative simulation method for the coherent contributions based on the rapid and partially analytic calculation of the second moments of large spin systems. We first validate the method on a simple system by predicting the 19F linewidth in CaF2 under MAS. We compare simulation results to experimental data for microcrystalline ubiquitin (deuterated 100% back-exchanged at 110 kHz and fully-protonated at 125 kHz). Our results quantitatively explain the observed linewidth per-residue basis for the vast majority of residues.
  • Multipole-moment effects in ion-molecule reactions at low temperatures: part III - the He+ + CH4 and He+ + CD4 reactions at low collision energies and the effect of the charge-octupole interaction
    Item type: Journal Article
    Zhelyazkova, Valentina; Martins, Fernanda B.V.; Merkt, Frédéric (2022)
    Physical Chemistry Chemical Physics
    We present experimental and theoretical studies of the He+ + CH4 and He+ + CD4 reactions at collision energies in the k(B).(0-10) K range. Helium atoms in a supersonic beam are excited to a low-field-seeking Rydberg-Stark state and merged with a supersonic beam of CH4 or CD4 using a curved surface-electrode deflector. The ion-molecule reactions are studied within the orbit of the helium Rydberg [He(n)] electron, which suppresses stray-electric-fields-induced heating and makes it possible to reach very low collision energies. The collision energy is varied by adjusting the velocity of the He(n) atoms with the surface deflector, keeping the velocity of the methane beam constant. The reaction product ions (C(H/D)(p)(+) with p epsilon {1,2,3}) are collected in a time-of-flight mass spectrometer and monitored as a function of the collision energy. No significant energy-dependence of the total reaction yields of either reactions is observed. The measured relative reaction rate coefficient for the He+ + CH4 reaction is approximately twice higher than the one for the He+ + CD4 reaction. The CH+, CH2+ and CH3+ (CD+, CD2+ and CD3+) ions were detected in ratios 0.28(+0.04) : 1.00(+0.11) : 0.11(+0.04) [0.35(+0.07) : 1.00(+0.16):0.04(-0.04)(+0.09)]. We also present calculations of the capture rate coefficients for the two reactions, in which the interaction between the charge of the helium ion and the octupole moment of the methane molecule is included. The rotational-state-specific capture rate coefficients are calculated for states with J = (0-3) at collision energies below k(B).15 K. After averaging over the rotational states of methane populated at the rotational temperature of the supersonic beam, the calculations only predict extremely weak enhancements (in the order of similar to 0.4%) of the rate coefficients compared to the Langevin rate constant k(L) over the collision-energy range considered.
  • Magnetic deflection of neutral sodium-doped ammonia clusters
    Item type: Journal Article
    Barnes, Jonathan V.; Beck, Martin; Hartweg, Sebastian; et al. (2021)
    Physical Chemistry Chemical Physics
    We describe the setup and the performance of a new pulsed Stern–Gerlach deflector and present results for small sodium-doped ammonia clusters Na(NH3)n (n = 1–4) in a molecular beam. NaNH3 shows the expected deflection of a spin ½ system, while all lager clusters show much smaller deflections. Experimental deflection ratios are compared with the values calculated from molecular dynamics simulations. The comparison reveals that intracluster spin relaxation in NaNH3 takes place on a time scale significantly longer than 200 μs. Assuming that intracluster relaxation is the cause of the reduced deflection, relaxation times seem to be on the order of 200 μs for all larger clusters Na(NH3)n (n = 2–4). Our work is a first attempt to understand the magnetic properties of isolated, weakly-bound clusters with relevance to the variety of diamagnetic and paramagnetic species expected in solvated electron systems.
  • In cell Gd3+-based site-directed spin labeling and EPR spectroscopy of eGFP
    Item type: Journal Article
    Kucher, Svetlana; Korneev, Sergej; Klare, Johann P.; et al. (2020)
    Physical Chemistry Chemical Physics
    Label-based functional studies of biomolecules in their native environment require labeling reactions inside living cells. In cell spin labeling using alkyne–azide click chemistry with a Gd3+-DOTAM-azide complex is shown to provide high spin label stability and narrow EPR lines for EPR spectroscopic detection of a spin labeled protein in living cells at ambient temperatures.
  • Spin-orbit interaction and Renner-Teller effect in HCCCCH+ studied by high-resolution photoelectron spectroscopy
    Item type: Journal Article
    Jacovella, Ugo; Merkt, Frédéric (2017)
    Physical Chemistry Chemical Physics
  • Ultrafast nuclear dynamics of the acetylene cation C2H2+ and its impact on the infrared probe pulse induced C–H bond breaking efficiency
    Item type: Journal Article
    Hartmann, Nadja; Bhattacharyya, Swarnendu; Schläpfer, Fabian; et al. (2019)
    Physical Chemistry Chemical Physics
    The ultrafast nuclear dynamics of the acetylene cation C2H2+ following photoionization of the neutral molecule is investigated using an extreme-ultraviolet pump/infrared probe setup. The observed modulation of the C2H+ fragment ion yield with pump–probe delay is related to structural changes induced by the extreme-ultraviolet pump pulse taking place on the femtosecond timescale. High-level simulations suggest that the trans-bending and C–C bond stretching motion of the C2H2+ cation govern the observed interaction with the infrared pulse. Depending on the molecular configuration at arrival of the infrared pulse, it either transfers population to higher-lying states or to the C2H2+ ground state, thereby enhancing or lowering the C2H+ yield. Our ultrafast pump–probe scheme can thus be used to track excited state nuclear dynamics with a resolution of a few femtoseconds, leading the way to studying fast dynamics also in larger hydrocarbon molecules.
  • Damage to fuel cell membranes
    Item type: Journal Article
    Dockheer, Sindy M.; Gubler, Lorenz; Bounds, Patricia L.; et al. (2010)
    Physical Chemistry Chemical Physics
  • Reinvestigation of the internal glycan rearrangement of Lewis a and blood group type H1 epitopes
    Item type: Journal Article
    Kontodimas, Vasilis; Yaman, Murat; Greis, Kim; et al. (2024)
    Physical Chemistry Chemical Physics
    Protonated ions of fucose-containing oligosaccharides are prone to undergo internal glycan rearrangement which results in chimeric fragments that obfuscate mass-spectrometric analysis. Lack of accessible tools that would facilitate systematic analysis of glycans in the gas phase limits our understanding of this phenomenon. In this work, we use density functional theory modeling to interpret cryogenic IR spectra of Lewis a and blood group type H1 trisaccharides and to establish whether these trisaccharides undergo the rearrangement during gas-phase analysis. Structurally unconstrained search reveals that none of the parent ions constitute a thermodynamic global minimum. In contrast, predicted collision cross sections and anharmonic IR spectra provide a good match to available experimental data which allowed us to conclude that fucose migration does not occur in these antigens. By comparing the predicted structures with those obtained for Lewis x and blood group type H2 epitopes, we demonstrate that the availability of the mobile proton and a large difference in the relative stability of the parent ions and rearrangement products constitute the prerequisites for the rearrangement reaction.
Publications1 - 10 of 436