Search results for "diatom"
showing 10 items of 156 documents
Quantum chemical simulations of hole self-trapping in semi-ionic crystals
1994
A novel formalism is presented for reliable calculations of the energetics of hole self-trapping in semi-ionic solids with mixed valence bands. Unlike previous model-Hamiltonian-type approaches, it is based on self-consistent quantum chemical INDO simulations of the atomistic and electronic structure of a self-trapped hole, making no a priori assumptions about a particular form of its localization (if any). This formalism is applied to the problem of hole self-trapping in corundum crystals (a -A1203). The hole self-trapping is found to be energetically favorable in the form of a diatomic 02 molecule with strong covalent bonding quite similar to the self-trapped hole (VK-center) in alkali ha…
Purely long-range polar molecules composed of identical lanthanide atoms
2019
International audience; Doubly polar molecules, possessing an electric dipole moment and a magnetic dipole moment, can strongly couple to both an external electric field and a magnetic field, providing unique opportunities to exert full control of the system quantum state at ultracold temperatures. We propose a method for creating a purely long-range doubly polar homonuclear molecule from a pair of strongly magnetic lanthanide atoms, one atom being in its ground level and the other in a superposition of quasi-degenerate opposite-parity excited levels [Phys. Rev. Lett. 121, 063201 (2018)]. The electric dipole moment is induced by coupling the excited levels with an external electric field. W…
Field-free molecular alignment for measuring ionization probability
2007
International audience; We have shown in a recent letter (Loriot et al 2006 Opt. Lett. 31 2897) the possibility of determining the ionization probability of linear molecules by using an all-optical technique that takes advantage of post-pulse molecular alignment. To that end, we have implemented a ‘cross-defocusing' technique producing a signal sensitive to both alignment and ionization. The analysis of the signal provides a quantitative measurement of the ionization probability calibrated with molecular alignment. In the present work, the method is discussed in more detail and applied to the measurement of the ionization probability of N2 as well as to the determination of the ionization r…
Direct theoretical evidence of nuclear motion in H+2by means of high harmonic generation
2007
The numerical solution of the time-dependent Schro ̈dinger equation for vibrating hydrogen molecular ions in many-cycle laser pulses shows that high- order harmonic generation is sensitive to laser-induced molecular vibrations. In particular, the odd harmonic lines in the emitted spectra are surrounded by additional regular peaks whose spacing is given by the vibrational frequency of the nuclei motion. Analytical theory relates these satellite peaks to the molecular vibrations in terms of an approximated effective potentials. These results are not affected by the dimensionality of the system.
Control of the high harmonic generation spectra by changing the molecule-laser field relative orientation
2010
The time dependent Schrodinger equation of a homonuclear diatomic molecule in the presence of a linearly polarized laser field is numerically solved by means of a split-operator parallel code. The calculations are carried out by assuming a single active electron model with fixed nuclei; a simplified two-dimensional model of the system is used. The highly nonlinear response of the electron wave function to the laser electric field stimulates the molecule to emit electromagnetic radiation consisting of a wide plateau of odd harmonics of the laser field. It is shown that the emitted spectrum can be finely controlled by changing the angle between the laser electric field and the molecular axis;…
Potential construction of the B (1) 1 Π state in KCs based on Fourier-Transform spectroscopy data
2015
Abstract The paper presents an empirical pointwise potential energy curve (PEC) of the extensively perturbed B ( 1 ) 1 Π state of the KCs molecule constructed by applying an Inverted Perturbation Approach routine. The experimental term values in the energy range E ( v ′ , J ′ ) ∈ [ 14071 ; 15502 ] cm − 1 involved in the fit were based on Fourier-Transform spectroscopy data obtained with 0.01 cm−1 accuracy from laser-induced B ( 1 ) 1 Π → X 1 Σ + fluorescence spectra in the present work (654 term values) combined with 520 term values from Birzniece et al. (2012) . The data set included vibrational v ′ ∈ [ 0 , 35 ] and rotational J ′ ∈ [ 7 , 233 ] quantum numbers covering about 85% of the pot…
Multiple-stressor effects on river biofilms under different hydrological conditions
2016
Summary We studied the relative importance of environmental factors (river flow, nutrients, dissolved organic matter) and organic micro-pollutants [herbicides, insecticides, industrial organic compounds, personal care products, antibiotics and pharmaceuticals, (PhCs)] to the structure and function of epilithic biofilms under various hydrological conditions and land uses. Biofilms from four river basins in the Iberian Peninsula (Llobregat, Ebro, Jucar and Guadalquivir) were analysed in summer–autumn during a wet period and base-flow conditions. The sites experienced different levels of pollution. We used variance partitioning (Redundancy Detrended Analysis, RDA) to link environmental stresso…
Environmental history of an urban lake: a palaeolimnological study of Lake Jyväsjärvi, Finland
2003
Sedimentary diatom frustules and chironomid remains, in addition to the chemical stratigraphy of 32 elements and organic pollutants such as resin acids, PCB, DDT and its metabolites, were studied from core samples taken from Lake Jyvasjarvi in Central Finland (64° 14′ N, 25° 47′ E). The sediment profile covered over 200 years, with the oldest samples representing a period of very low human interference. The town of Jyvaskyla was established on the lake shore in 1837, and the lake received untreated municipal wastewater from the town up until, 1977. A paper mill started operations in 1872 and began discharging effluent into Lake Jyvasjarvi. In recent years this effluent loading has been redu…
Spontaneous lifetimes and relaxation cross-sections of the D1Π state of NaRb
2003
Abstract The time-resolved intensity of dispersed laser induced fluorescence following the Ar + -laser D 1 Π←X 1 Σ + excitation was measured for both 23 Na 85 Rb and 23 Na 87 Rb isotopomers in a thermal cell. Spontaneous radiative lifetime values determined for v ′ ( J ′ ) rovibronic levels of the D 1 Π state in the v ′ range from 0 to 17 and J ′ from 8 to 131 varied from 22.5 to 17.3 ns. Averaged collisional quenching cross-section values of (3–6)×10 −14 cm 2 were obtained for NaRb (D 1 Π, v ′ , J ′ ) + Rb collisions from the Stern–Volmer plots.
Molecular dynamics studies of 3D quasicrystals
1993
Abstract The thermodynamic behaviour of monatomic and diatomic models of three-dimensional icosahedral quasicrystals has been studied in NVT and NPT ensembles using molecular dynamics simulations with atoms interacting via Lennard-Jones potentials. We also report on a microcanonical MD simulation of decagonal Al 65 Cu 20 Co 15 quasicrystals where an experimentally determined binary model has been used. To obtain stability in this latter case it is necessary to endow the atoms with effective pair potentials. No transitions to crystalline or amorphous phases were found for diatomic models. Monatomic models, however, display a certain stability only in the low-temperature region. In the range …