36 research outputs found
Improved Potential Energy Surface of Ozone Constructed Using the Fitting by Permutationally Invariant Polynomial Function
New global potential energy surface for the ground electronic state of ozone is constructed at the complete basis set level of the multireference configuration interaction theory. A method of fitting the data points by analytical permutationally invariant polynomial function is adopted. A small set of 500 points is preoptimized using the old surface of ozone. In this procedure the positions of points in the configuration space are chosen such that the RMS deviation of the fit is minimized. New ab initio calculations are carried out at these points and are used to build new surface. Additional points are added to the vicinity of the minimum energy path in order to improve accuracy of the fit, particularly in the region where the surface of ozone exhibits a shallow van der Waals well. New surface can be used to study formation of ozone at thermal energies and its spectroscopy near the dissociation threshold
Formation of H by radiative association of H and H in the interstellar medium
We develop the theory of radiative association of an atom and a diatomic
molecule within a close-coupling framework. We apply it to the formation of
H after the low energy collision (below 0.5 eV) of H with H.
Using recently obtained potential energy and permanent dipole moment surfaces
of H, we calculate the lowest rovibrational levels of the H
electronic ground state, and the cross section for the formation of H by
radiative association between H and ortho- and para-H. We discuss the
possibility for the H ion to be formed and observed in the cold and dense
interstellar medium in an environment with a high ionization rate. Such an
observation would be a probe for the presence of H in the interstellar
medium
Heat and moisture diffusion in spruce and wood panels computed from 3-D morphologies using the Lattice Boltzmann method
International audienceIn this paper, the Lattice Boltzmann method is used to simulate heat and mass diffusion in bio-based building materials. The numerical method is presented and the methodology developed to reduce the calculation time is described. The 3-D morphologies of spruce and wood fibers are obtained using synchrotron X-ray micro-to-mography. Equivalent macroscopic properties (heat conductivity and mass diffusivity) are therefore determined from the real micro-structure of the materials. The results reveal the anisotropy of the studied materials. The computed equivalent heat conductivity varies from − − 0.036 W m K 1 1 to − − 0.52 W m K 1 1 and the computed di-mensionless mass diffusivity varies from 0.0088 to 0.78 depending on the materials and on the diffusion directions. Using these results, morphology families are identified and simple expressions are proposed to predict the equivalent properties as a function of phase properties and solid fraction
Potential energy and dipole moment surfaces of H3- molecule
A new potential energy surface for the electronic ground state of the
simplest triatomic anion H3- is determined for a large number of geometries.
Its accuracy is improved at short and large distances compared to previous
studies. The permanent dipole moment surface of the state is also computed for
the first time. Nine vibrational levels of H3- and fourteen levels of D3- are
obtained, bound by at most ~70 cm^{-1} and ~ 126 cm^{-1} respectively. These
results should guide the spectroscopic search of the H3- ion in cold gases
(below 100K) of molecular hydrogen in the presence of H3- ions
Cross sections and rate coefficients for vibrational excitation of h<inf>2</inf>o by electron impact
Cross-sections and thermally averaged rate coefficients for vibration (de-)excitation of a water molecule by electron impact are computed; one and two quanta excitations are considered for all three normal modes. The calculations use a theoretical approach that combines the normal mode approximation for vibrational states of water, a vibrational frame transformation employed to evaluate the scattering matrix for vibrational transitions and the UK molecular R-matrix code. The interval of applicability of the rate coefficients is from 10 to 10,000 K. A comprehensive set of calculations is performed to assess uncertainty of the obtained data. The results should help in modelling non-LTE spectra of water in various astrophysical environments
Formation of H-3(-) by radiative association of H-2 and H- in the interstellar medium
We develop the theory of radiative association of an atom and a diatomic molecule within a close-coupling framework. We apply it to the formation of H-3(-) after the low-energy collision (below 0.5 eV) of H-2 with H-. Using recently obtained potential energy and permanent dipole moment surfaces of H-3(-), we calculate the lowest rovibrational levels of the H-3(-) electronic ground state and the cross section for the formation of H-3(-) by radiative association between H- and ortho- and para-H-2. We discuss the possibility for the H-3(-) ion to be formed and observed in the cold and dense interstellar medium in an environment with a high ionization rate. Such an observation could be a probe for the presence of H- in the interstellar medium
Reactive collisions between electrons and BeH+ above dissociation threshold
Our previous studies of dissociative recombination, and vibrational
excitation/de-excitation of the BeH ion, based on the multichannel quantum
defect theory, are extended to collision energies above the dissociation
threshold, taking into account the vibrational continua of the BeH ion and,
consequently, its dissociative excitation. We have also significantly increased
the number of dissociative states of , and
symmetry included in our cross section calculations, generating the most
excited-ones by using appropriate scaling laws. Our results are suitable for
modeling the kinetics of BeH+ in edge fusion plasmas for collision energies up
to 12 eV.Comment: 9 pages, 9 figures
Potential energy and dipole moment surfaces of HCO- for the search of H- in the interstellar medium
Potential energy and permanent dipole moment surfaces of the electronic ground state of formyl negative ion HCO- are determined for a large number of geometries using the coupled-cluster theory with single and double and perturbative treatment of triple excitations ab initio method with a large basis set. The obtained data are used to construct interpolated surfaces, which are extended analytically to the region of large separations between CO and H- with the multipole expansion approach. We have calculated the energy of the lowest rovibrational levels of HCO- that should guide the spectroscopic characterization of HCO- in laboratory experiments. The study can also help to detect HCO- in the cold and dense regions of the interstellar medium where the anion could be formed through the association of abundant CO with still unobserved H-
Dissociative recombination of NH: A revisited study
Dissociative recombination of NH is explored in a two-step
theoretical study. In a first step, a diatomic (1D) rough model with frozen NN
bond and frozen angles is adopted, in the framework of the multichannel quantum
defect theory (MQDT). The importance of the indirect mechanism and of the
bending mode is revealed, in spite of the disagreement between our cross
section and the experimental one. In a second step, we use our recently
elaborated 3D approach based on the normal mode approximation combined with
R-matrix theory and MQDT. This approach results in satisfactory agreement with
storage-ring measurements, significantly better at very low energy than the
former calculations.Comment: 9 pages, 5 figures, 1 tabl