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

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 (C$_7$H$_5$N) [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_nX (n = 6−9; X = V, Mn)

We present a combined experimental and theoretical investigation of small neutral vanadium and manganese doped silicon clusters SinX (n = 6−9, 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 Si₆B

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, 2A′) 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 für Infrarotspektroskopie

Breitbandig durchstimmbare Infrarotstrahlung im mittleren Wellenlängenbereich von etwa 3 bis 10 μm bzw. 1000 bis3200 Wellenzahlen ist ein hochinteressantes Mittel zur spektroskopischen Untersuchung gasförmiger, flüssiger 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 kohärenter Laserquellen in einem miniaturisierten Aufbau. Als mögliche Anwendungen werden aktuell berührungslose und zerstörungsfreie Echtzeit-Identifikation explosiver Substanzen sowie online und inline Detektion von Öl-Kontaminationen in Wasser untersucht und entwickelt