Time filter

Source Type

Madrid, Spain

Hernandez Vera M.,CNRS Laboratory of Waves and Complex Media | Hernandez Vera M.,Instituto Superior Of Tecnologias Y Ciencias Aplicadas | Lique F.,CNRS Laboratory of Waves and Complex Media | Dumouchel F.,CNRS Laboratory of Waves and Complex Media | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

Modelling molecular abundances in the interstellar medium (ISM) requires accurate moleculardata. Then, accurate determination of collisional rate coefficients is an essential stepin order to estimate the cyanide/isocyanide abundances in interstellar clouds. In addition,cyanides/isocyanides are the most common metal-containing molecules in circumstellar gas.In this work, we have carried out calculations of rate coefficients for the rotational excitationof aluminium cyanide (AlCN), aluminium isocyanide (AlNC), magnesium cyanide (MgCN)and magnesium isocyanide (MgNC) molecules in collision with He. The calculations arebased on new two-dimensional potential energy surfaces obtained from highly correlated abinitio calculations. Coupled states quantum approximation was used to obtain pure rotational(de-)excitation cross-sections of AlCN, AlNC, MgCN and MgNC by He. The fine structuresplitting of MgCN and MgNC was taken into account through a technique based on infiniteordersudden scaling relationship. Rate coefficients for transitions among the first 26 rotationallevels of AlCN and AlNC and among the first 41 fine structure levels ofMgCN andMgNCwerecalculated for the temperature range between 5 and 100 K. Significant differences betweenthe rate coefficients of both isomers were observed. These differences confirm that specificcalculations have to be performed for each isomer in order to obtain the necessary level ofdetail. The new rate coefficients should induce important consequences on the determinationof metal abundance in the ISM. In particular, our work confirms that the AlCN molecule issignificantly less abundant than AlNC in the ISM. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Bizzeti P.G.,University of Florence | De Angelis G.,National Institute of Nuclear Physics, Italy | Lenzi S.M.,University of Padua | Orlandi R.,IEM CSIC
Physical Review C - Nuclear Physics | Year: 2012

The assumption of an exact isospin symmetry would imply equal strengths for mirror E1 transitions (at least, in the long-wavelength limit). Actually, large violations of this symmetry rule have been indicated by a number of experimental results, the last of which is the 67As-67Se doublet investigated at GAMMASPHERE. Here, we examine in detail various possible origins of the observed asymmetry. The coherent effect of Coulomb-induced mixing with the high-lying giant isovector monopole resonance is proposed as the most probable process to produce a large asymmetry in the E1 transitions, with comparatively small effect on the other properties of the parent and daughter levels. © 2012 American Physical Society. Source

Spielfiedel A.,Paris-Sorbonne University | Senent M.L.,IEM CSIC | Kalugina Y.,CNRS Laboratory of Waves and Complex Media | Kalugina Y.,Tomsk State University | And 5 more authors.
Journal of Chemical Physics | Year: 2015

We compute a new potential energy surface (PES) for the study of the inelastic collisions between N2H+ and H2 molecules. A preliminary study of the reactivity of N2H+ with H2 shows that neglecting reactive channels in collisional excitation studies is certainly valid at low temperatures. The four dimensional (4D) N2H+-H2 PES is obtained from electronic structure calculations using the coupled cluster with single, double, and perturbative triple excitation level of theory. The atoms are described by the augmented correlation consistent triple zeta basis set. Both molecules were treated as rigid rotors. The potential energy surface exhibits a well depth of ≃2530 cm-1. Considering this very deep well, it appears that converged scattering calculations that take into account the rotational structure of both N2H+ and H2 should be very difficult to carry out. To overcome this difficulty, the "adiabatic-hindered-rotor" treatment, which allows para-H2(j = 0) to be treated as if it were spherical, was used in order to reduce the scattering calculations to a 2D problem. The validity of this approach is checked and we find that cross sections and rate coefficients computed from the adiabatic reduced surface are in very good agreement with the full 4D calculations. © 2015 AIP Publishing LLC. Source

Moorthi K.,Mitsui Chemicals Inc. | Kamio K.,MC Anac | Ramos J.,IEM CSIC | Theodorou D.N.,National Technical University of Athens
AIP Conference Proceedings | Year: 2013

Atomistic models of short chain branched (SCB) polyethylene melts containing up to 20-40 mol% of comonomer (1-butene, 1-hexene, 1-octene or 1-decene) have been equilibrated at 450 K using a connectivity altering Monte Carlo method, and analyzed for topological constraints using Z1 and CReTA codes. The calculated tube diameters, 〈app〉, of SCB melts are found to scale with the backbone weight fraction, , as 〈a pp〉∼-0.46, close to the scaling predicted by the binary contact model, 〈app〉∼-0.5 and in disagreement with the packing model prediction 〈app〉∼ -1.27. Similar scaling relationships are observed experimentally for polymer solutions, and reproduced by the present methods. © 2013 American Institute of Physics. Source

Senent M.L.,IEM CSIC | Dumouchel F.,University of Le Havre | Lique F.,University of Le Havre
Monthly Notices of the Royal Astronomical Society | Year: 2012

Modelling molecular abundances in the interstellar medium requires accurate molecular data. In this work, structural and spectroscopic properties of a series of metal cyanides/isocyanide species containing Na, Mg, Al and Si are calculated and compared using highly correlated ab initio calculations. The metal substitution effect on molecular properties is discussed. Isomerization pathways and transitions states are detailed. NaCN shows three isomeric structures, one T shaped and two linear forms, whereas the remaining compounds display two linear minimum energy geometries. For the first time, NaCN secondary minima are described. Second-order perturbation theory spectroscopic parameters are determined from an anharmonic RCCSD(T)/aug-cc-pV5Z force field. Very accurate rotational constants are calculated using a complete basis set and taking into account vibrational effects and the structure variation with core electron correlation. For l-SiCN and l-SiNC, spin-orbit parameters are also provided. Present theoretical results are compared with available experimental data attaining a good agreement. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS. Source

Discover hidden collaborations