32,528 research outputs found
Conserved Vibrational Coherence in the Ultrafast Rearrangement of 2-Nitrotoluene Radical Cation
2-Nitrotoluene (2-NT) is a good model for both photolabile protecting groups for organic synthesis and the military explosive 2,4,6-trinitrotoluene (TNT). In addition to the direct CâNO2 bond-cleavage reaction that initiates detonation in TNT, 2-NT undergoes an H atom attack reaction common to the photolabile 2-nitrobenzyl group, which forms the aci-nitro tautomer. In this work, femtosecond pumpâprobe measure- ments with mass spectrometric detection and density functional theory (DFT) calculations demonstrate that the initially prepared vibrational coherence in the 2-NT radical cation (2- NT+) is preserved following H atom attack. Strong-field adiabatic ionization is used to prepare 2-NT+, which can overcome a modest 0.76 eV energy barrier to H atom attack to form the aci-nitro tautomer as soon as âŒ20â60 fs after ionization. Once formed, the aci-nitro tautomer spontaneously loses âOH to form C7H6NO+, which exhibits distinctly faster oscillations in its ion yield (290 fs period) as compared to the 2-NT+ ion (380 fs period). The fast oscillations are attributed to the coherent torsional motion of the aci-nitro tautomer, which has a significantly faster computed torsional frequency (86.9 cmâ1) than the 2- NT+ ion (47.9 cmâ1). Additional DFT calculations identify reaction pathways leading to the formation of the dissociation products C7H6NO+, C7H7+, and C6H6N+. Collectively, these results reveal a rich picture of coherently and incoherently driven dissociation pathways in 2-NT+
Threshold behavior in metastable dissociation of multi-photon ionized thymine and uracil
Microsecond-timescale HNCO loss has been observed from single-color multi-photon ionized pyrimidine nucleobases in the gas phase. Photon energy thresholds for the metastable channels have been measured at 5.55 ± 0.02 eV for thymine and 5.57 ± 0.02 eV for uracil. We argue that these results can be attributed to accessing the moleculesâ S1 states with additional vibrational energy matching the threshold energy for HNCO loss from the radical cation. Combined with previous photoionization energies, this enables the S1 adiabatic energies to be deduced: 3.67 ± 0.07 eV for thymine and 3.77 ± 0.07 eV for uracil. These values are consistent with recent calculations
Thermal, electric and spin transport in superconductor/ferromagnetic-insulator structures
A ferromagnetic insulator (FI) attached to a conventional superconductor (S)
changes drastically the properties of the latter. Specifically, the exchange
field at the FI/S interface leads to a splitting of the superconducting density
of states. If S is a superconducting film, thinner than the superconducting
coherence length, the modification of the density of states occurs over the
whole sample. The co-existence of the exchange splitting and superconducting
correlations in S/FI structures leads to striking transport phenomena that are
of interest for applications in thermoelectricity, superconducting spintronics
and radiation sensors. Here we review the most recent progress in understanding
the transport properties of FI/S structures by presenting a complete
theoretical framework based on the quasiclassical kinetic equations. We discuss
the coupling between the electronic degrees of freedom, charge, spin and
energy, under non-equilibrium conditions and its manifestation in
thermoelectricity and spin-dependent transport.Comment: 117 pages, 33 figures. arXiv admin note: substantial text overlap
with arXiv:1706.0824
Observation of Spin Hall Effect in Weyl Semimetal WTe2 at Room Temperature
Discovery of topological Weyl semimetals has revealed the opportunities to
realize several extraordinary physical phenomena in condensed matter physics.
Specifically, these semimetals with strong spin-orbit coupling, broken
inversion symmetry and novel spin texture are predicted to exhibit a large spin
Hall effect that can efficiently convert the charge current to a spin current.
Here we report the direct experimental observation of a large spin Hall and
inverse spin Hall effects in Weyl semimetal WTe2 at room temperature obeying
Onsager reciprocity relation. We demonstrate the detection of the pure spin
current generated by spin Hall phenomenon in WTe2 by making van der Waals
heterostructures with graphene, taking advantage of its long spin coherence
length and spin transmission at the heterostructure interface. These
experimental findings well supported by ab initio calculations show a large
charge-spin conversion efficiency in WTe2; which can pave the way for
utilization of spin-orbit induced phenomena in spintronic memory and logic
circuit architectures
Proceedings of the Thirteenth International Conference on Time-Resolved Vibrational Spectroscopy
The thirteenth meeting in a long-standing series of âTime-Resolved Vibrational Spectroscopyâ (TRVS) conferences was held May 19th to 25th at the Kardinal Döpfner Haus in Freising, Germany, organized by the two Munich Universities - Ludwig-Maximilians-UniversitĂ€t and Technische UniversitĂ€t MĂŒnchen. This international conference continues the illustrious tradition of the original in 1982, which took place in Lake Placid, NY. The series of meetings was initiated by leading, world-renowned experts in the field of ultrafast laser spectroscopy, and is still guided by its founder, Prof. George Atkinson (University of Arizona and Science and Technology Advisor to the Secretary of State). In its current format, the conference contributes to traditional areas of time resolved vibrational spectroscopies including infrared, Raman and related laser methods. It combines them with the most recent developments to gain new information for research and novel technical applications. The scientific program addressed basic science, applied research and advancing novel commercial applications.
The thirteenth conference on Time Resolved Vibrational Spectroscopy promoted science in the areas of physics, chemistry and biology with a strong focus on biochemistry and material science. Vibrational spectra are molecule- and bond-specific. Thus, time-resolved vibrational studies provide detailed structural and kinetic information about primary dynamical processes on the picometer length scale. From this perspective, the goal of achieving a complete understanding of complex chemical and physical processes on the molecular level is well pursued by the recent progress in experimental and theoretical vibrational studies.
These proceedings collect research papers presented at the TRVS XIII in Freising, German
In-situ acoustic-based analysis system for physical and chemical properties of the lower Martian atmosphere
The Environmental Acoustic Reconnaissance and Sounding experiment (EARS), is
composed of two parts: the Environmental Acoustic Reconnaissance (EAR)
instrument and the Environmental Acoustic Sounding Experiment (EASE). They are
distinct, but have the common objective of characterizing the acoustic
environment of Mars. The principal goal of the EAR instrument is "listening" to
Mars. This could be a most significant experiment if one thinks of everyday
life experience where hearing is possibly the most important sense after sight.
Not only will this contribute to opening up this important area of planetary
exploration, which has been essentially ignored up until now, but will also
bring the general public closer in contact with our most proximate planet. EASE
is directed at characterizing acoustic propagation parameters, specifically
sound velocity and absorption, and will provide information regarding important
physical and chemical parameters of the lower Martian atmosphere; in
particular, water vapor content, specific heat capacity, heat conductivity and
shear viscosity, which will provide specific constraints in determining its
composition. This would enable one to gain a deeper understanding of Mars and
its analogues on Earth. Furthermore, the knowledge of the physical and chemical
parameters of the Martian atmosphere, which influence its circulation, will
improve the comprehension of its climate now and in the past, so as to gain
insight on the possibility of the past presence of life on Mars. These aspect
are considered strategic in the contest of its exploration, as is clearly
indicated in NASA's four main objectives on "Long Term Mars Exploration
Program" (http://marsweb.jpl.nasa.gov/mer/science).Comment: 16 pages including figure
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