50 research outputs found
Adsorption von CO2, N2O und D2O an MgO(100)-Einkristallspaltflächen : Polarisations-Infrarotspektroskopie, Beugung langsamer Elektronen, Spektren- und Strukturberechnungen
[no abstract
Infrared action spectroscopy of doubly charged PAHs and their contribution to the aromatic infrared bands
The so-called aromatic infrared bands are attributed to emission of
polycyclic aromatic hydrocarbons. The observed variations toward different
regions in space are believed to be caused by contributions of different
classes of PAH molecules, i.e. with respect to their size, structure, and
charge state. Laboratory spectra of members of these classes are needed to
compare them to observations and to benchmark quantum-chemically computed
spectra of these species. In this paper we present the experimental infrared
spectra of three different PAH dications, naphthalene,
anthracene, and phenanthrene, in the vibrational fingerprint
region 500-1700~cm. The dications were produced by electron impact
ionization of the vapors with 70 eV electrons, and they remained stable against
dissociation and Coulomb explosion. The vibrational spectra were obtained by IR
predissociation of the PAH complexed with neon in a 22-pole cryogenic
ion trap setup coupled to a free-electron infrared laser at the Free-Electron
Lasers for Infrared eXperiments (FELIX) Laboratory. We performed anharmonic
density-functional theory calculations for both singly and doubly charged
states of the three molecules. The experimental band positions showed excellent
agreement with the calculated band positions of the singlet electronic ground
state for all three doubly charged species, indicating its higher stability
over the triplet state. The presence of several strong combination bands and
additional weaker features in the recorded spectra, especially in the
10-15~m region of the mid-IR spectrum, required anharmonic calculations to
understand their effects on the total integrated intensity for the different
charge states. These measurements, in tandem with theoretical calculations,
will help in the identification of this specific class of doubly-charged PAHs
as carriers of AIBs.Comment: Accepted for publication in A&
Terahertz optically pumped silicon lasers
Stimulated terahertz (THz) emission from silicon single crystals doped by group-V donors has been obtained by optical excitation with pulsed infrared lasers. Pumping by a conventional TEA CO2 laser results in lasing on discrete lines between 1.3 and 7 THz (see figure). Laser thresholds can be as low as 10 kW/cm2. They depend on the donors species and the laser mechanism. Intracentre population inversion is realized between particular excited states which are large-spaced due to the chemical shift of the donor binding energy. The lifetime of an electron in an excited state (up to ~70 ps) is determined by the efficiency of phonon-assisted nonradiative relaxation. Optical excitation by the emission of a frequency-tunable free electron laser results in two different types of lasing. At relatively low pump intensities (~1 kW/cm2) the intracentre mechanism of lasing is dominating. At pump intensities above ~100 kW/cm2 stimulated scattering of pump photons on transverse acoustic intervalley phonons can occur in the vicinity of an impurity atom. This results in laser emission in the frequency range from 4.6 to 5.8 THz. In this case the laser frequency can be tuned proportionally to the pump frequency
以書付奉伺候(十五軒程当時相休居候、旅籠取立云々)
Superposition of orbital eigenstates is crucial to quantum technology utilizing atoms, such as
atomic clocks and quantum computers, and control over the interaction between atoms and
their neighbours is an essential ingredient for both gating and readout. The simplest coherent
wavefunction control uses a two-eigenstate admixture, but more control over the spatial
distribution of the wavefunction can be obtained by increasing the number of states in the
wavepacket. Here we demonstrate THz laser pulse control of Si:P orbitals using multiple
orbital state admixtures, observing beat patterns produced by Zeeman splitting. The beats are
an observable signature of the ability to control the path of the electron, which implies we
can now control the strength and duration of the interaction of the atom with different
neighbours. This could simplify surface code networks which require spatially controlled
interaction between atoms, and we propose an architecture that might take advantage of this
The significance of the amorphous potential energy landscape for dictating glassy dynamics and driving solid-state crystallisation.
The fundamental origins surrounding the dynamics of disordered solids near their characteristic glass transitions continue to be fiercely debated, even though a vast number of materials can form amorphous solids, including small-molecule organic, inorganic, covalent, metallic, and even large biological systems. The glass-transition temperature, Tg, can be readily detected by a diverse set of techniques, but given that these measurement modalities probe vastly different processes, there has been significant debate regarding the question of why Tg can be detected across all of them. Here we show clear experimental and computational evidence in support of a theory that proposes that the shape and structure of the potential-energy surface (PES) is the fundamental factor underlying the glass-transition processes, regardless of the frequency that experimental methods probe. Whilst this has been proposed previously, we demonstrate, using ab initio molecular-dynamics (AIMD) simulations, that it is of critical importance to carefully consider the complete PES - both the intra-molecular and inter-molecular features - in order to fully understand the entire range of atomic-dynamical processes in disordered solids. Finally, we show that it is possible to utilise this dependence to directly manipulate and harness amorphous dynamics in order to control the behaviour of such solids by using high-powered terahertz pulses to induce crystallisation and preferential crystal-polymorph growth in glasses. Combined, these findings provide compelling evidence that the PES landscape, and the corresponding energy barriers, are the ultimate controlling feature behind the atomic and molecular dynamics of disordered solids, regardless of the frequency at which they occur
Resonant infrared laser-induced desorption of methane condensed on nacl(100): Isotope mixture experiments
Contains fulltext :
98848.pdf (publisher's version ) (Open Access
Spectroscopy of the low-frequency vibrational modes of CH3+ isotopologues
The low-frequency stretching and bending vibrations of the isotopologues CH2D+,CD2H+ and CH3+ have been recorded at low temperature and low resolution. For this, a cryogenic 22-pole trapping machine coupled to an IR beamline of the FELIX free electron laser facility has been used. To record the overview spectra, the laser induced reactions CDmHn+ + H-2 -> (hv) CDm-1Hn+1+ + HD have been applied for these species. As this scheme is not applicable to CH3+, the latter has been tagged with He and subsequently dissociated by the IR beam. For the resulting CH3+-He spectrum, broad features are observed below 1000 cm(-1) possibly related to vibrational motions involving the He atom. The extracted vibrational band positions for all species are compared to results from high-level quantum-chemical calculations. (C) 2018 Elsevier Inc. All rights reserved
Hidden harmonic quantum states in proteins: Did Davydov get the sign wrong?
Contains fulltext :
176672.pdf (publisher's version ) (Closed access