Ruth Signorell

Last Name

Signorell

First Name

Ruth

ORCID

0000-0003-1111-9261

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03961 - Signorell, Ruth / Signorell, Ruth

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Publications1 - 10 of 196

Electric Charge Effect on the Water Mass Transfer across Mixed Aqueous–Organic Droplet Interfaces
Azizbaig Mohajer, Mercede; Gleichweit, Michael; David, Grégory; et al. (2025)
The Journal of Physical Chemistry A
Understanding gas-particle mass transport is essential for predicting aerosol behavior in the atmosphere and in industrial processes. The mass accommodation coefficient, αM, is a key parameter describing this exchange. Defined as the probability of a gas-phase molecule adhering to a particle upon collision, αMpresents a highly surface-sensitive property. Aqueous atmospheric aerosol droplets carry electric charges, which accumulate near the surface; however, their influence on the gas-particle mass transport remains elusive. To access the influence of charge on αM, we combined an aerosol charging method with photothermal single-particle spectroscopy, enabling direct water mass exchange measurements on the surface of single aerosol droplets. We investigated charged and neutral aqueous glycerol and tetraethylene glycol droplets across a wide range of concentrations and temperatures. The micrometre-sized droplets carried approximately 10³elementary charges─exceeding typical atmospheric aerosol charge levels─yet our results show that αMis independent of the droplet charge and instead is dominated by composition and temperature. Theoretical estimates of the charge-dipole and dipole–dipole interaction energies corroborate this finding, highlighting that under atmospherically relevant conditions, electric charge plays a negligible role in the mass accommodation process.
Acceleration of butane vapor nucleation by carbon dioxide gas
Choudhury, Arnab; Graber, Felix; Feusi, Stefan; et al. (2025)
Physical Chemistry Chemical Physics
Carbon dioxide (CO2) gas is known to strongly accelerate nucleation of other gas phase components, such as water and toluene. The acceleration was attributed to the formation of transient heteromolecular dimers and referred to as the chaperon mechanism. In this work, we investigate this phenomenon for butane-CO2 gas mixtures with mass spectrometry in the post-nozzle flow of a Laval expansion at a temperature of 51 K and a pressure of 40 Pa. At moderate CO2 and butane concentrations, we observed an acceleration of butane nucleation by the chaperon mechanism, albeit only by a factor of about two compared to unary butane nucleation. The fact that the chaperon mechanism is less important for butane than for water and toluene can be rationalized by the weaker intermolecular interactions between butane and CO2. At higher CO2 and butane concentrations, nucleation and cluster growth overlap in time, which leads to saturation of the measured total butane concentration. Using a kinetic model, we show that saturation is caused by the formation of heteromolecular butane-CO2 clusters of different sizes and compositions. Studies on nucleation at low temperatures in such systems are relevant for flue or natural gas separation.
Development of an experimental setup for the direct observation of gas phase nucleation
Schläppi, Bernhard; Litman, Jessica H.; Signorell, Ruth (2014)
Abstracts of Papers of the American Chemical Society
Dynamics of submicron aerosol droplets in a robust optical trap formed by multiple Bessel beams
Thanopulos, Ioannis; Luckhaus, David; Preston, Thomas C.; et al. (2014)
Journal of Applied Physics
In this paper, we model the three-dimensional escape dynamics of single submicron-sized aerosol droplets in optical multiple Bessel beam traps. Trapping in counter-propagating Bessel beams (CPBBs) is compared with a newly proposed quadruple Bessel beam (QBB) trap, which consists of two perpendicularly arranged CPBB traps. Calculations are performed for perfectly and imperfectly aligned traps. Mie-theory and finite-difference time-domain methods are used to calculate the optical forces. The droplet escape kinetics are obtained from the solution of the Langevin equation using a Verlet algorithm. Provided the traps are perfectly aligned, the calculations indicate very long lifetimes for droplets trapped either in the CPBB or in the QBB trap. However, minor misalignments that are hard to control experimentally already severely diminish the stability of the CPBB trap. By contrast, such minor misalignments hardly affect the extended droplet lifetimes in a QBB trap. The QBB trap is found to be a stable, robust optical trap, which should enable the experimental investigation of submicron droplets with radii down to 100 nm. Optical binding between two droplets and its potential role in preventing coagulation when loading a CPBB trap is briefly addressed.
Comment on: Is the Hydrated Electron Vertical Detachment Genuinely Bimodal? J. Phys. Chem. Lett. 2019, 10, 4910-4913
Signorell, Ruth (2020)
In a recent article, David Bartels addresses the issue of the band shape of the genuine binding energy spectrum of the hydrated electron. He essentially claims that the genuine binding energy of the hydrated electron must be Gaussian in shape independent of the photon energy used for ionization, contrary to what was found in our previous work for excitations energies in the UV (3.6-5.8 eV photon energy). Further, he alleges that the asymmetric (bimodal) distribution found for the genuine binding energy in our previous work must have resulted from deficiencies in the scattering cross sections used in the scattering calculations. Bartels concludes that these deficiencies arise from an allegedly wrong value of -1.0eV for the escape barrier used in the original fitting procedure to determine the scattering cross section. In the following, we show that these claims are unfounded and based on partly incorrect assumptions.
Assessing relative humidity dependent photoacoustics to retrieve mass accommodation coefficients of single optically trapped aerosol particles
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.
Photoacoustics of single laser-trapped nanodroplets for the direct observation of nanofocusing in aerosol photokinetics
Cremer, Johannes; Thaler, Klemens M.; Haisch, Christoph; et al. (2016)
Nature Communications
Photochemistry taking place in atmospheric aerosol droplets has a significant impact on the Earth’s climate. Nanofocusing of electromagnetic radiation inside aerosols plays a crucial role in their absorption behaviour, since the radiation flux inside the droplet strongly affects the activation rate of photochemically active species. However, size-dependent nanofocusing effects in the photokinetics of small aerosols have escaped direct observation due to the inability to measure absorption signatures from single droplets. Here we show that photoacoustic measurements on optically trapped single nanodroplets provide a direct, broadly applicable method to measure absorption with attolitre sensitivity. We demonstrate for a model aerosol that the photolysis is accelerated by an order of magnitude in the sub-micron to micron size range, compared with larger droplets. The versatility of our technique promises broad applicability to absorption studies of aerosol particles, such as atmospheric aerosols where quantitative photokinetic data are critical for climate predictions.
Magnetic deflection of neutral sodium-doped ammonia clusters
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.
Photoacoustics of single aerosol droplets immobilised by counter-propagating optical tweezers
Diveky, Matus; Gleichweit, Michael; Roy, Sandra; et al. (2020)
Optical Trapping and Optical Micromanipulation XVII ~ Proceedings Volume c, Optical Trapping and Optical Micromanipulation XVII; 1146316 (2020)
In this contribution we discuss the influence of relative humidity on photoacoustic measurements from both an experimental and theoretical perspective. We present a refined model of the photoacoustic (PA) signal that accounts for elevated particle temperatures and different levels of relative humidity. We use this new model together with the photoacoustic data collected with our photothermal single-particle spectrometer (PSPS) to retrieve the mass accommodation coefficients of water on organic aerosol particles. The single-particle nature of our experiments is achieved by employing counter-propagating tweezers. Furthermore, we investigate the influence of relative humidity on the eigenfrequency of the PA cell.
Carbon Dioxide and Propane Nucleation: The Emergence of a Nucleation Barrier
Krohn, Jan; Lippe, Martina; Li, Chenxi; et al. (2020)
Physical Chemistry Chemical Physics

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Ruth Signorell

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