1,326 research outputs found
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Enabling liquid vapor analysis using synchrotron VUV single photon ionization mass spectrometry with a microfluidic interface.
Vacuum ultraviolet (VUV) single photon ionization mass spectrometry (SPI-MS) is a vacuum-based technique typically used for the analysis of gas phase and solid samples, but not for liquids due to the challenge in introducing volatile liquids in a vacuum. Here we present the first demonstration of in situ liquid analysis by integrating the System for Analysis at the Liquid Vacuum Interface (SALVI) microfluidic reactor into VUV SPI-MS. Four representative volatile organic compound (VOC) solutions were used to illustrate the feasibility of liquid analysis. Our results show the accurate mass identification of the VOC molecules and the reliable determination of appearance energy that is consistent with ionization energy for gaseous species in the literature as reported. This work validates that the vacuum-compatible SALVI microfluidic interface can be utilized at the synchrotron beamline and enable the in situ study of gas-phase molecules evaporating off the surface of a liquid, which holds importance in the study of condensed matter chemistry
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Low-temperature formation of polycyclic aromatic hydrocarbons in Titan’s atmosphere
The detection of benzene in Titan’s atmosphere led to the emergence of polycyclic aromatic hydrocarbons (PAHs) as potential nucleation agents triggering the growth of Titan’s orange-brownish haze layers. However, the fundamental mechanisms leading to the formation of PAHs in Titan’s low-temperature atmosphere have remained elusive. We provide persuasive evidence through laboratory experiments and computations that prototype PAHs like anthracene and phenanthrene (C14H10) are synthesized via barrierless reactions involving naphthyl radicals (C10H7•) with vinylacetylene (CH2=CH–C≡CH) in low-temperature environments. These elementary reactions are rapid, have no entrance barriers, and synthesize anthracene and phenanthrene via van der Waals complexes and submerged barriers. This facile route to anthracene and phenanthrene—potential building blocks to complex PAHs and aerosols in Titan—signifies a critical shift in the perception that PAHs can only be formed under high-temperature conditions, providing a detailed understanding of the chemistry of Titan’s atmosphere by untangling elementary reactions on the most fundamental level
Study of the , , and in the radiative decays
In this paper we present an approach to study the radiative decay modes of
the into a photon and one of the tensor mesons ,
, as well as the scalar ones and .
Especially we compare predictions that emerge from a scheme where the states
appear dynamically in the solution of vector meson--vector meson scattering
amplitudes to those from a (admittedly naive) quark model. We provide evidence
that it might be possible to distinguish amongst the two scenarios, once
improved data are available.Comment: The large Nc argument improved; version published in EPJA
Note: Position dependence of time signals picked off a microchannel plate detector
Citation: Ablikim, U., Zohrabi, M., Jochim, B., Berry, B., Severt, T., Carnes, K. D., & Ben-Itzhak, I. (2015). Note: Position dependence of time signals picked off a microchannel plate detector. Review of Scientific Instruments, 86(1), 3. doi:10.1063/1.4906327Using an ultrafast laser and a precision mask, we demonstrate that time signals picked off directly from a microchannel plate detector depend on the position of the hit. This causes a time spread of about 280 ps, which can affect the quality of imaging measurements using large detectors. (C) 2015 AIP Publishing LLC
Carrier-envelope phase control over pathway interference in strong-field dissociation of H
The dissociation of an H molecular-ion beam by linearly polarized,
carrier-envelope-phase-tagged 5 fs pulses at 4W/cm with a
central wavelength of 730 nm was studied using a coincidence 3D momentum
imaging technique. Carrier-envelope-phase-dependent asymmetries in the emission
direction of H fragments relative to the laser polarization were observed.
These asymmetries are caused by interference of odd and even photon number
pathways, where net-zero photon and 1-photon interference predominantly
contributes at H+H kinetic energy releases of 0.2 -- 0.45 eV, and
net-2-photon and 1-photon interference contributes at 1.65 -- 1.9 eV. These
measurements of the benchmark H molecule offer the distinct advantage
that they can be quantitatively compared with \textit{ab initio} theory to
confirm our understanding of strong-field coherent control via the
carrier-envelope phase
Note: Determining the detection efficiency of excited neutral atoms by a microchannel plate detector
Citation: Berry, B., Zohrabi, M., Hayes, D., Ablikim, U., Jochim, B., Severt, T., . . . Ben-Itzhak, I. (2015). Note: Determining the detection efficiency of excited neutral atoms by a microchannel plate detector. Review of Scientific Instruments, 86(4), 3. doi:10.1063/1.4916953We present a method for determining the detection efficiency of neutral atoms relative to keV ions. Excited D* atoms are produced by D-2 fragmentation in a strong laser field. The fragments are detected by a micro-channel plate detector either directly as neutrals or as keV ions following field ionization and acceleration by a static electric field. Moreover, we propose a new mechanism by which neutrals are detected. We show that the ratio of the yield of neutrals and ions can be related to the relative detection efficiency of these species. (C) 2015 AIP Publishing LLC
Fragmentation of CD+ induced by intense ultrashort laser pulses
Citation: Graham, L., Zohrabi, M., Gaire, B., Ablikim, U., Jochim, B., Berry, B., . . . Ben-Itzhak, I. (2015). Fragmentation of CD+ induced by intense ultrashort laser pulses. Physical Review A, 91(2), 11. doi:10.1103/PhysRevA.91.023414The fragmentation of CD[superscript +] in intense ultrashort laser pulses was investigated using a coincidence three-dimensional momentum imaging technique improved by employing both transverse and longitudinal electric fields. This allowed clear separation of all fragmentation channels and the determination of the kinetic energy release down to nearly zero, for a molecule with significant mass asymmetry. The most probable dissociation pathways for the two lowest dissociation limits, C[superscript +]+D and C+D[superscript +], were identified for both 22-fs, 798-nm and 50-fs, 392-nm pulses. Curiously, the charge asymmetric dissociation of CD[superscript 2+] was not observed for 392-nm photons, even though it was clearly visible for the fundamental 798 nm at the same peak intensity
Identification of absolute geometries of cis and trans molecular isomers by Coulomb Explosion Imaging
Citation: Ablikim, U., Bomme, C., Xiong, H., Savelyev, E., Obaid, R., Kaderiya, B., . . . Rolles, D. (2016). Identification of absolute geometries of cis and trans molecular isomers by Coulomb Explosion Imaging. Scientific Reports, 6, 8. doi:10.1038/srep38202An experimental route to identify and separate geometric isomers by means of coincident Coulomb explosion imaging is presented, allowing isomer-resolved photoionization studies on isomerically mixed samples. We demonstrate the technique on cis/trans 1,2-dibromoethene (C2H2Br2). The momentum correlation between the bromine ions in a three-body fragmentation process induced by bromine 3d inner-shell photoionization is used to identify the cis and trans structures of the isomers. The experimentally determined momentum correlations and the isomer-resolved fragment-ion kinetic energies are matched closely by a classical Coulomb explosion model
Adaptive strong-field control of chemical dynamics guided by three-dimensional momentum imaging.
Shaping ultrafast laser pulses using adaptive feedback can manipulate dynamics in molecular systems, but extracting information from the optimized pulse remains difficult. Experimental time constraints often limit feedback to a single observable, complicating efforts to decipher the underlying mechanisms and parameterize the search process. Here we show, using two strong-field examples, that by rapidly inverting velocity map images of ions to recover the three-dimensional photofragment momentum distribution and incorporating that feedback into the control loop, the specificity of the control objective is markedly increased. First, the complex angular distribution of fragment ions from the nω+C2D4→C2D3++D interaction is manipulated. Second, isomerization of acetylene (nω+C2H2→C2H22+→CH2++C+) is controlled via a barrier-suppression mechanism, a result that is validated by model calculations. Collectively, these experiments comprise a significant advance towards the fundamental goal of actively guiding population to a specified quantum state of a molecule
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