12 research outputs found
Directional States of Symmetric-Top Molecules Produced by Combined Static and Radiative Electric Fields
We show that combined electrostatic and radiative fields can greatly amplify
the directional properties, such as axis orientation and alignment, of
symmetric top molecules. In our computational study, we consider all four
symmetry combinations of the prolate and oblate inertia and polarizability
tensors, as well as the collinear and perpendicular (or tilted) geometries of
the two fields. In, respectively, the collinear or perpendicular fields, the
oblate or prolate polarizability interaction due to the radiative field forces
the permanent dipole into alignment with the static field. Two mechanisms are
found to be responsible for the amplification of the molecules' orientation,
which ensues once the static field is turned on: (a) permanent-dipole coupling
of the opposite-parity tunneling doublets created by the oblate polarizability
interaction in collinear static and radiative fields; (b) hybridization of the
opposite parity states via the polarizability interaction and their coupling by
the permanent dipole interaction to the collinear or perpendicular static
field. In perpendicular fields, the oblate polarizability interaction, along
with the loss of cylindrical symmetry, is found to preclude the wrong-way
orientation, causing all states to become high-field seeking with respect to
the static field. The adiabatic labels of the states in the tilted fields
depend on the adiabatic path taken through the parameter space comprised of the
permanent and induced-dipole interaction parameters and the tilt angle between
the two field vectors
Uncertainties in mechanics and materials research. Application in the field of materials research
Theoretical description of adiabatic laser alignment and mixed-field orientation: the need for a non-adiabatic model
We present a theoretical study of recent laser-alignment and
mixed-field-orientation experiments of asymmetric top molecules. In these
experiments, pendular states were created using linearly polarized strong ac
electric fields from pulsed lasers in combination with weak electrostatic
fields. We compare the outcome of our calculations with experimental results
obtained for the prototypical large molecule benzonitrile (CHN) [J.L.
Hansen et al, Phys. Rev. A, 83, 023406 (2011)] and explore the directional
properties of the molecular ensemble for several field configurations, i.e.,
for various field strengths and angles between ac and dc fields. For
perpendicular fields one obtains pure alignment, which is well reproduced by
the simulations. For tilted fields, we show that a fully adiabatic description
of the process does not reproduce the experimentally observed orientation, and
it is mandatory to use a diabatic model for population transfer between
rotational states. We develop such a model and compare its outcome to the
experimental data confirming the importance of non-adiabatic processes in the
field-dressed molecular dynamics.Comment: 11 pages, 9 figure
The structures of neutral transition metal doped silicon clusters, Si<sub>n</sub>X (n = 6â9; X = V, Mn)
We present a combined experimental and theoretical investigation of small neutral vanadium and manganese doped silicon clusters SinX (n = 6â9, X = V, Mn). These species are studied by infrared multiple photon dissociation and mass spectrometry. Structural identification is achieved by comparison of the experimental data with computed infrared spectra of low-lying isomers using density functional theory at the B3P86/6-311+G(d) level. The assigned structures of the neutral vanadium and manganese doped silicon clusters are compared with their cationic counterparts. In general, the neutral and cationic SinV0,+ and SinMn0,+ clusters have similar structures, although the position of the capping atoms depends for certain sizes on the charge state. The influence of the charge state on the electronic properties of the clusters is also investigated by analysis of the density of states, the shapes of the molecular orbitals, and NBO charge analysis of the dopant atom
Characterization of neutral boron-silicon clusters using infrared spectroscopy: The case of Si<sub>6</sub>B
Nano-size clusters are of great interest for understanding of fundamental properties and processes relevant for applied materials science such as heterogeneous catalysis. In this study, we present a newly developed dual-target dual-laser ablation source, suitable for the production of binary clusters and their spectroscopic characterization. With the current design, an almost arbitrary mixing ratio can be achieved by altering different parameters such as the laser fluences. Boron and silicon targets are chosen for cluster production, illustrating the possibility to control the outcome ranging from pure boron over mixed SinBm to pure silicon clusters. As a test system, Si6B clusters are characterized by means of infrared-ultraviolet two-color ionization (IR-UV2CI) spectroscopy, combined with quantum chemical simulations. The most stable structure of Si6B (Cs, 2AâČ) predicted in our previous work is confirmed by the present experiment. Doping of Si7 with a single B atom has a drastic impact on the geometric, vibrational, and electronic properties
Miniaturisierte Laserlichtquelle fĂŒr Infrarotspektroskopie
Breitbandig durchstimmbare Infrarotstrahlung im mittleren WellenlĂ€ngenbereich von etwa 3 bis 10 ÎŒm bzw. 1000 bis3200 Wellenzahlen ist ein hochinteressantes Mittel zur spektroskopischen Untersuchung gasförmiger, flĂŒssiger oderfester Stoffe und Gemische. In diesem Beitrag wird eine weit durchstimmbare Infrarotlichtquelle auf Basis eines Quantenkaskadenlasers(QCL) und eines mikro-opto-elektro-mechanischen (MOEMS) Gitters vorgestellt. Dieses Konzeptvereint Vorteile breitbandiger Quellen mit Vorteilen kohĂ€renter Laserquellen in einem miniaturisierten Aufbau. Als mögliche Anwendungen werden aktuell berĂŒhrungslose und zerstörungsfreie Echtzeit-Identifikation explosiver Substanzen sowie online und inline Detektion von Ăl-Kontaminationen in Wasser untersucht und entwickelt