134 research outputs found
Closed-loop recycling of rare liquid samples for gas-phase experiments
Many samples of current interest in molecular physics and physical chemistry exist in the liquid phase and are vaporized for use in gas cells, diffuse gas targets, or molecular gas jets. For some of these techniques, the large sample consumption is a limiting factor. When rare, expensive molecules such as custom-made chiral molecules or species with isotopic labels are used, wasting them in the exhaust line of the pumps is quite an expensive and inefficient approach. Therefore, we developed a closed-loop recycling system for molecules with vapor pressures below atmospheric pressure. Once filled, only a few valves have to be adjusted, and a cold trap must be moved after each phase of recycling. The recycling efficiency per turn exceeds 95%
A setup for studies of photoelectron circular dichroism from chiral molecules in aqueous solution
We present a unique experimental design that enables the measurement of photoelectron circular dichroism (PECD) from chiral molecules in aqueous solution. The effect is revealed from the intensity difference of photoelectron emission into a backward-scattering angle relative to the photon propagation direction when ionizing with circularly polarized light of different helicity. This leads to asymmetries (normalized intensity differences) that depend on the handedness of the chiral sample and exceed the ones in conventional dichroic mechanisms by orders of magnitude. The asymmetry is largest for photon energies within several electron volts above the ionization threshold. A primary aim is to explore the effect of hydration on PECD. The modular and flexible design of our experimental setup EASI (Electronic structure from Aqueous Solutions and Interfaces) also allows for detection of more common photoelectron angular distributions, requiring distinctively different detection geometries and typically using linearly polarized light. A microjet is used for liquid-sample delivery. We describe EASI’s technical features and present two selected experimental results, one based on synchrotron-light measurements and the other performed in the laboratory, using monochromatized He-II α radiation. The former demonstrates the principal effectiveness of PECD detection, illustrated for prototypic gas-phase fenchone. We also discuss the first data from liquid fenchone. In the second example, we present valence photoelectron spectra from liquid water and NaI aqueous solution, here obtained from a planar-surface microjet (flatjet). This new development features a more favorable symmetry for angle-dependent photoelectron measurements
A measurement of the evolution of Interatomic Coulombic Decay in the time domain
During the last 15 years a novel decay mechanism of excited atoms has been
discovered and investigated. This so called ''Interatomic Coulombic Decay''
(ICD) involves the chemical environment of the electronically excited atom: the
excitation energy is transferred (in many cases over long distances) to a
neighbor of the initially excited particle usually ionizing that neighbor. It
turned out that ICD is a very common decay route in nature as it occurs across
van-der-Waals and hydrogen bonds. The time evolution of ICD is predicted to be
highly complex, as its efficiency strongly depends on the distance of the atoms
involved and this distance typically changes during the decay. Here we present
the first direct measurement of the temporal evolution of ICD using a novel
experimental approach.Comment: 6 pages, 4 figures, submitted to PR
Vibrationally Resolved Decay Width of Interatomic Coulombic Decay in HeNe
We investigate the ionization of HeNe from below the He 1s3p excitation to
the He ionization threshold. We observe HeNe ions with an enhancement by
more than a factor of 60 when the He side couples resonantly to the radiation
field. These ions are an experimental proof of a two-center resonant
photoionization mechanism predicted by Najjari et al. [Phys. Rev. Lett. 105,
153002 (2010)]. Furthermore, our data provide electronic and vibrational state
resolved decay widths of interatomic Coulombic decay (ICD) in HeNe dimers. We
find that the ICD lifetime strongly increases with increasing vibrational
state.Comment: 7 pages, 5 figure
Vibrationally Resolved Inner-Shell Photoexcitation of the Molecular Anion C
Carbon core-hole excitation of the molecular anion C has been
experimentally studied at high resolution by employing the photon-ion
merged-beams technique at a synchrotron light source. The experimental cross
section for photo--double-detachment shows a pronounced vibrational structure
associated with and core
excitations of the C ground level and first excited level, respectively.
A detailed Franck-Condon analysis reveals a strong contraction of the C
molecular anion by 0.2~\AA\ upon this core photoexcitation. The associated
change of the molecule's moment of inertia leads to a noticeable rotational
broadening of the observed vibrational spectral features. This broadening is
accounted for in the present analysis which provides the spectroscopic
parameters of the C and
core-excited levels.Comment: 8 pages, 5 figures, 1 table, accepted for publication in ChemPhysChe
Ion impact induced Interatomic Coulombic Decay in neon and argon dimers
We investigate the contribution of Interatomic Coulombic Decay induced by ion
impact in neon and argon dimers (Ne and Ar) to the production of low
energy electrons. Our experiments cover a broad range of perturbation strengths
and reaction channels. We use 11.37 MeV/u S, 0.125 MeV/u He,
0.1625 MeV/u He and 0.150 MeV/u He as projectiles and study
ionization, single and double electron transfer to the projectile as well as
projectile electron loss processes. The application of a COLTRIMS reaction
microscope enables us to retrieve the three-dimensional momentum vectors of the
ion pairs of the fragmenting dimer into Ne/Ne and
Ar/Ar (q = 1, 2, 3) in coincidence with at least one emitted
electron
X-Ray Photoabsorption of Density-sensitive Metastable States in Ne VII, Fe XXII, and Fe XXIII
Metastable states of ions can be sufficiently populated in absorbing and emitting astrophysical media, enabling spectroscopic plasma-density diagnostics. Long-lived states appear in many isoelectronic sequences with an even number of electrons, and can be fed at large rates by various photonic and electronic mechanisms. Here, we experimentally investigate beryllium-like and carbon-like ions of neon and iron that have been predicted to exhibit detectable features in astrophysical soft X-ray absorption spectra. An ion population generated and excited by electron impact is subjected to highly monochromatic X-rays from a synchrotron beamline, allowing us to identify Kα transitions from metastable states. We compare their energies and natural line widths with state-of-the-art theory and benchmark level population calculations at electron densities of 1010.5 cm-3
Influence of the emission site on the photoelectron circular dichroism in trifluoromethyloxirane
We report a joint experimental and theoretical study of the differential photoelectron circular dichroism (PECD) in inner-shell photoionization of uniaxially oriented trifluoromethyloxirane. By adjusting the photon energy of the circularly polarized synchrotron radiation, we address 1s-photoionization of the oxygen, different carbon, and all fluorine atoms. The photon energies were chosen such that in all cases electrons with a similar kinetic energy of about 11 eV are emitted. Employing coincident detection of electrons and fragment ions, we concentrate on identical molecular fragmentation channels for all of the electron-emitter scenarios. Thereby, we systematically examine the influence of the emission site of the photoelectron wave on the differential PECD. We observe large differences in the PECD signals. The present experimental results are supported by corresponding relaxed-core Hartree–Fock calculations. This article is part of the themed collection: Festschrift Ivan Powis: Advances in Molecular Photoelectron Spectroscopy: Fundamentals & Applicatio
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