24 research outputs found
Solution of the Time-Dependent Schrödinger Equation for Highly Symmetric Potentials
The method of symmetry adapted wavepackets (SAWP) to solve the time-dependent Schrödinger equation for a highly symmetric potential energy surface is introduced. The angular dependence of a quantum-mechanical wavepacket is expanded in spherical harmonics where the number of close-coupled equations for the corresponding radial functions can be efficiently reduced by symmetry adaption of the rotational basis using the SAWP approach. Various techniques to generate symmetry adapted spherical harmonics (SASHs) for the point groups of highest symmetry (octahedral, icosahedral) are discussed. The standard projection operator technique involves the use of Wigner rotation matrices. Two methods to circumvent numerical instabilities occuring for large azimuthal quantum numbers are suggested. The first is based on a numerical scheme which employs Gaussian integrations yielding exact and stable results. The second is a recursive algorithm to generate higher order SASHs accurately and efficiently from lower order ones. The paper gives a complete set of ``seed functions'' generated by projection techniques which can be used to obtain SASHs for all irreducible representations of the octahedral and icosahedral point groups recursively
Complex time method for quantum dynamics when an exceptional point is encircled in the parameter space
We revisit the complex time method for the application to quantum dynamics as
an exceptional point is encircled in the parameter space of the Hamiltonian.
The basic idea of the complex time method is using complex contour integration
to perform the first-order adiabatic perturbation integral. In this way, the
quantum dynamical problem is transformed to a study of singularities in the
complex time plane -- transition points -- which represent complex degeneracies
of the adiabatic Hamiltonian as the time-dependent parameters defining the
encircling contour are analytically continued to complex plane. As an
underlying illustration of the approach we discuss a switch between Rabi
oscillations and rapid adiabatic passage which occurs upon the encircling of an
exceptional point in a special time-symmetric case.Comment: My paper includes 71 pages and 24 figures out of which 21 pages and 4
figures are Appendixe
Photolysis of Hydrogen Chloride Embedded in the First Argon Solvation Shell: Rotational Control and Quantum Dynamics of Photofragments
Under standard conditions reaction yields are connected with terms like free energy differences and thermal distributions. However, many modern experimental techniques, such as supersonic beam expansion or matrix isolation, deal with cryogenic temperatures and isolated reactants in inert clusters or solid matrices. Under these conditions the photochemical reaction mechanism is in many cases strongly dependent on the shape of delocalized initial vibrational or rotational wavefunctions of the reactants which can be employed for an efficient reaction yield control. Here, we apply, using quantum molecular dynamics simulations,such a scheme to the rotational control of photolysis of the HCl molecule embedded in an icosahedral Ar12cluster. First, the HCl molecule is preexcited into a specific low lying rotational level. Depending on the rotational state, the hydrogen probability is enhanced in different directions within the cluster. In a second step, the HCl molecule is photolyzed by a UV pulse. The rapidly dissociating hydrogen atom reaches then primarily either the holes in the solvent shell or the argon atoms, depending on the rotational preexcitation. Starting either from the ground or from the first totally symmetric excited rotational states, the direct dissociation and the delayed process accompanied with a temporary trapping of the hydrogen atom have very different relative yields. As a consequence, differences up to a factor of five in the temporary population of the hydrogen atom inside the cluster after the first hydrogen - cage collision are observed. In the energy domain a significant difference in the structure of the kinetic energy distribution spectra, connected with the existence of short-lived vibrational resonances of the hydrogen atom, is predicted
Librational control of photochemical reactions in small clusters
A novel approach to the control of photochemical reaction yield in hydrogen containing clusters is outlined and applied to the process of the Cl2 molecule formation from a UV photolyzed Cl...HCl species. The control mechanism consists in a far-IR preexcitation of the large amplitude hydrogenic bending (librational) mode prior to the HCl photodissociation, leading to more than a factor of two enhancement of the Cl2 yield both in the parent and deuterated cluster
A high-resolution infrared spectroscopic investigation of the halogen atom-HCN entrance channel complexes solvated in superfluid helium droplets
Rotationally resolved infrared spectra are reported for the X-HCN (X = Cl,
Br, I) binary complexes solvated in helium nanodroplets. These results are
directly compared with that obtained previously for the corresponding X-HF
complexes [J. M. Merritt, J. K\"upper, and R. E. Miller, PCCP, 7, 67 (2005)].
For bromine and iodine atoms complexed with HCN, two linear structures are
observed and assigned to the and ground
electronic states of the nitrogen and hydrogen bound geometries, respectively.
Experiments for HCN + chlorine atoms give rise to only a single band which is
attributed to the nitrogen bound isomer. That the hydrogen bound isomer is not
stabilized is rationalized in terms of a lowering of the isomerization barrier
by spin-orbit coupling. Theoretical calculations with and without spin-orbit
coupling have also been performed and are compared with our experimental
results. The possibility of stabilizing high-energy structures containing
multiple radicals is discussed, motivated by preliminary spectroscopic evidence
for the di-radical Br-HCCCN-Br complex. Spectra for the corresponding molecular
halogen HCN-X complexes are also presented.Comment: 20 pages, 15 figures, 6 tables, RevTe
Entrance Channel X-HF (X=Cl, Br, and I) Complexes studied by High-Resolution Infrared Laser Spectroscopy in Helium Nanodroplets
Rotationally resolved infrared spectra are reported for halogen atom - HF
free radical complexes formed in helium nanodroplets. An effusive pyrolysis
source is used to dope helium droplets with Cl, Br and I atoms, formed by
thermal dissociation of Cl, Br and I. A single hydrogen fluoride
molecule is then added to the droplets, resulting in the formation of the X-HF
complexes of interest. Analysis of the resulting spectra confirms that the
observed species have ground electronic states, consistent with
the linear hydrogen bound structures predicted from theory. Stark spectra are
also reported for these species, from which the permanent electric dipole
moments are determined.Comment: 41 pages, 16 figures, 5 table
Trueness and precision of the real-time RT-PCR method for quantifying the chronic bee paralysis virus genome in bee homogenates evaluated by a comparative inter-laboratory study
The Chronic bee paralysis virus (CBPV) is the aetiological agent of chronic bee paralysis, a contagious disease associated with nervous disorders in adult honeybees leading to massive mortalities in front of the hives. Some of the clinical signs frequently reported, such as trembling, may be confused with intoxication syndromes. Therefore, laboratory diagnosis using real-time PCR to quantify CBPV loads is used to confirm disease. Clinical signs of chronic paralysis are usually associated with viral loads higher than 108 copies of CBPV genome copies per bee (8 log(10) CBPV/bee). This threshold is used by the European Union Reference Laboratory for Bee Health to diagnose the disease. In 2015, the accuracy of measurements of three CBPV loads (5, 8 and 9 log(10) CBPV/bee) was assessed through an inter-laboratory study. Twenty-one participants, including 16 European National Reference Laboratories, received 13 homogenates of CBPV-infected bees adjusted to the three loads. Participants were requested to use the method usually employed for routine diagnosis. The quantitative results (n = 270) were analysed according to international standards NF ISO 13528 (2015) and NF ISO 5725-2 (1994). The standard deviations of measurement reproducibility (S-R) were 0.83, 1.06 and 1.16 at viral loads 5, 8 and 9 log(10) CBPV/bee, respectively. The inter-laboratory confidence of viral quantification (+/- 1.96 S-R) at the diagnostic threshold (8 log(10) CBPV/bee) was +/- 2.08 log(10) CBPV/bee. These results highlight the need to take into account the confidence of measurements in epidemiological studies using results from different laboratories. Considering this confidence, viral loads over 6 log(10) CBPV/bee may be considered to indicate probable cases of chronic paralysis
A pan-European epidemiological study reveals honey bee colony survival depends on beekeeper education and disease control
Reports of honey bee population decline has spurred many national efforts to understand the extent of the problem and to identify causative or associated factors. However, our collective understanding of the factors has been hampered by a lack of joined up trans-national effort. Moreover, the impacts of beekeeper knowledge and beekeeping management practices have often been overlooked, despite honey bees being a managed pollinator. Here, we established a standardised active monitoring network for 5 798 apiaries over two consecutive years to quantify honey bee colony mortality across 17 European countries. Our data demonstrate that overwinter losses ranged between 2% and 32%, and that high summer losses were likely to follow high winter losses. Multivariate Poisson regression models revealed that hobbyist beekeepers with small apiaries and little experience in beekeeping had double the winter mortality rate when compared to professional beekeepers. Furthermore, honey bees kept by professional beekeepers never showed signs of disease, unlike apiaries from hobbyist beekeepers that had symptoms of bacterial infection and heavy Varroa infestation. Our data highlight beekeeper background and apicultural practices as major drivers of honey bee colony losses. The benefits of conducting trans-national monitoring schemes and improving beekeeper training are discussed