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1.
Phys Rev Lett ; 124(1): 013402, 2020 Jan 10.
Artigo em Inglês | MEDLINE | ID: mdl-31976689

RESUMO

The high surface sensitivity and controlled surface charge state of submicron sized droplets is exploited to study low-energy electron transport through liquid interfaces using photoelectron imaging. Already a few charges on a droplet are found to modify the photoelectron images significantly. For narrow escape barriers, the comparison with an electron scattering model reveals pronounced quantum effects in the form of above-barrier reflections at electron kinetic energies below about 1 eV. The observed susceptibility to the characteristics of the electron escape barrier might provide access to these properties for liquid interfaces, which are generally difficult to investigate.

2.
J Phys Chem A ; 124(39): 7959-7965, 2020 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-32878434

RESUMO

Below band gap formation of solvated electrons in neutral water clusters using pump-probe photoelectron imaging is compared with recent data for liquid water and with above band gap excitation studies in liquid and clusters. Similar relaxation times on the order of 200 fs and 1-2 ps are retrieved for below and above band gap excitation, in both clusters and liquid. The independence of the relaxation times from the generation process indicates that these times are dominated by the solvent response, which is significantly slower than the various solvated electron formation processes. The analysis of the temporal evolution of the vertical electron binding energy and the electron binding energy at half-maximum suggests a dependence of the solvation time on the binding energy.

3.
Phys Chem Chem Phys ; 20(24): 16364-16371, 2018 Jun 20.
Artigo em Inglês | MEDLINE | ID: mdl-29872831

RESUMO

Low-energy electron scattering in water clusters (H2O)n with average cluster sizes of n < 700 is investigated by angle-resolved photoelectron spectroscopy using high harmonic radiation at photon energies of 14.0, 20.3, and 26.5 eV for ionization from the three outermost valence orbitals. The measurements probe the evolution of the photoelectron anisotropy parameter ß as a function of cluster size. A remarkably steep decrease of ß with increasing cluster size is observed, which for the largest clusters reaches liquid bulk values. Detailed electron scattering calculations reveal that neither gas nor condensed phase scattering can explain the cluster data. Qualitative agreement between experiment and simulations is obtained with scattering calculations that treat cluster scattering as an intermediate case between gas and condensed phase scattering.

4.
Phys Chem Chem Phys ; 20(37): 24019-24026, 2018 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-30221282

RESUMO

The para-dinitrobenzene radical anion has been studied by 2D photoelectron imaging within the energy range of 2.5 eV above the detachment threshold. Supporting electronic structure calculations at the XMCQDPT2 level of the excited states and resonances are presented. The direct photodetachment channel has been observed and modelled, and yields an electron affinity of 1.99 ± 0.01 eV. In addition to the direct channel, evidence of resonances is observed. These resonances, which are symmetry allowed for photoexcitation from the ground state and of Feshbach types with respect to the open continuum, result in fast internal conversion to bound electronic states, followed by statistical electron emission observed at very low kinetic energies as well as dissociation of the nitrite anion. The latter is seen in the photoelectron spectra, which can be modelled as a combination of direct detachment from the para-dinitrobenzene and nitrite anions. An additional dimension has been offered by the 2D photoelectron angular distribution that is particularly sensitive to a mechanism of electron detachment, allowing us to confidently interpret the production of the nitrite anion photofragment.

5.
J Phys Chem Lett ; 10(17): 4777-4782, 2019 Sep 05.
Artigo em Inglês | MEDLINE | ID: mdl-31382737

RESUMO

We have investigated the solvation dynamics and the genuine binding energy and photoemission anisotropy of the solvated electron in neutral water clusters with a combination of time-resolved photoelectron velocity map imaging and electron scattering simulations. The dynamics was probed with a UV probe pulse following above-band-gap excitation by an EUV pump pulse. The solvation dynamics is completed within about 2 ps. Only a single band is observed in the spectra, with no indication for isomers with distinct binding energies. Data analysis with an electron scattering model reveals a genuine binding energy in the range of 3.55-3.85 eV and a genuine anisotropy parameter in the range of 0.51-0.66 for the ground-state hydrated electron. All of these observations coincide with those for liquid bulk, which is rather unexpected for an average cluster size of 300 molecules.

6.
Biosensors (Basel) ; 5(2): 187-98, 2015 Apr 13.
Artigo em Inglês | MEDLINE | ID: mdl-25871832

RESUMO

Despite the fact that the theoretical foundations of the sensitivity of waveguide grating based (bio)sensors are well-known, understood and their implications anticipated by the scientific community since several decades, to our knowledge, no prior publication has experimentally confirmed waveguide sensitivity for multiple film thicknesses, wavelengths and polarization of the propagating light. In this paper, the bulk refractive index sensitivity versus waveguide thickness of said refractometric sensors is experimentally determined and compared with predictions based on established theory. The effective refractive indices and the corresponding sensitivity were determined via the sensors' coupling angles at different cover refractive indices for transverse electric as well as transverse magnetic polarized illumination at various wavelengths in the visible and near-infrared. The theoretical sensitivity was calculated by solving the mode equation for a three layer waveguide.


Assuntos
Técnicas Biossensoriais/instrumentação , Refratometria/instrumentação , Modelos Teóricos , Dispositivos Ópticos , Fenômenos Ópticos
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