EXCITATION COLLISIONNELLE DES ATOMES ET DES MOLÉCULES DANS LE MILIEU INTERSTELLAIRE (ASPECT THÉORIQUE)

Récemment, des progrès ont été accomplis dans la détermination théorique de l'excitation collisionnelle des transitions de structure fine et des transitions de rotation pour les molécules d'intérêt astrophysique. Les surfaces d'énergie potentielle des systèmes comportant peu d'électrons sont accessibles aux méthodes ab initio et le calcul de la collision peut être envisagé par les méthodes quantiques, pour des énergies basses et des systèmes légers

Ultracold collisions between Li atoms and Li2 diatoms in high vibrational states

International audienceWe have performed a quantum-dynamical study of vibrational deexcitation and elastic scattering at ultralow collision energies for the bosonic system Li7+Li27 and for the fermionic system Li6+Li26 with diatomic molecules in high vibrational states. Inelastic rates show a strong and irregular dependence on the vibrational state of the diatomic molecule. For the highest vibrational state which lies near the dissociation limit, vibrational deexcitation processes are not suppressed, but rather depleted, for both bosonic and fermionic systems

Full dimension Rb2He ground triplet potential energy surface and quantum scattering calculations

International audienceWe have developed a three-dimensional potential energy surface for the lowest triplet state of the Rb2He complex. A global analytic fit is provided as in the supplementary material [see supplementary material at http://dx.doi.org/10.1063/1.4709433E-JCPSA6-136-034218 for the corresponding Fortran code]. This surface is used to perform quantum scattering calculations of 4He and 3He colliding with 87Rb2 in the partial wave J = 0 at low and ultralow energies. For the heavier helium isotope, the computed vibrational relaxation probabilities show a broad and strong shape resonance for a collisional energy of 0.15 K and a narrow Feshbach resonance at about 17 K for all initial Rb2 vibrational states studied. The broad resonance corresponds to an efficient relaxation mechanism that does not occur when 3He is the colliding partner. The Feshbach resonance observed at higher collisional energy is robust with respect to the isotopic substitution. However, its effect on the vibrational relaxation mechanism is faint for both isotopes

Ultracold collisions involving heteronuclear alkali metal dimers

We have carried out the first quantum dynamics calculations on ultracold atom-diatom collisions in isotopic mixtures. The systems studied are spin-polarized 7Li + 6Li7Li, 7Li + 6Li2, 6Li + 6Li7Li and 6Li + 7Li2. Reactive scattering can occur for the first two systems even when the molecules are in their ground rovibrational states, but is slower than vibrational relaxation in homonuclear systems. Implications for sympathetic cooling of heteronuclear molecules are discussed.Comment: 4 pages, 3 figure

Polar molecule reactive collisions in quasi-1D systems

We study polar molecule scattering in quasi-one-dimensional geometries. Elastic and reactive collision rates are computed as a function of collision energy and electric dipole moment for different confinement strengths. The numerical results are interpreted in terms of first order scattering and of adiabatic models. Universal dipolar scattering is also discussed. Our results are relevant to experiments where control of the collision dynamics through one dimensional confinement and an applied electric field is envisioned.Comment: 25 pages, 13 figure

Feshbach resonances in ultracold atom-molecule collisions

We investigate the presence of Feshbach resonances in ultracold alkali-dialkali reactive collisions. Quantum scattering calculations are performed on a new Na_3 quartet potential energy surface. An analysis of scattering features is performed through a systematic variation of the nonadditive three-body interaction potential. Our results should provide useful information for interpreting future atom-molecule collision experiments.Comment: 7 pages, 6 figure

A detailed quantum mechanical and quasiclassical trajectory study on the dynamics of the H(+) + H2 --> H2 + H(+) exchange reaction

13 pages, 11 figures.-- PACS nrs.: 82.30.Hk; 82.30.Nr.The H(+) + H2 exchange reaction has been studied theoretically by means of a different variety of methods as an exact time independent quantum mechanical, approximate quantum wave packet, statistical quantum, and quasiclassical trajectory approaches. Total and state-to-state reaction probabilities in terms of the collision energy for different values of the total angular momentum obtained with these methods are compared. The dynamics of the reaction is extensively studied at the collision energy of E(coll) = 0.44 eV. Integral and differential cross sections and opacity functions at this collision energy have been calculated. In particular, the fairly good description of the exact quantum results provided by the statistical quantum method suggests that the dynamics of the process is governed by an insertion mechanism with the formation of a long-lived collision complex.Two of the authors (O.R. and T.G.L.) thank the Spanish Ministry of Education (MEC) for financial support through Grants Nos. FIS2004-02461 and CTQ2004-02415. One of the authors (T.G.L.) would like to acknowledge support from the program Ramón y Cajal of Spanish MEC and EU Grant No. MERG-CT-2004-513600. Two other authors (F.J.A. and L.B.) acknowledge financial support through MEC Grant No. CTQ2005-08493-C02-01 and Universidad Complutense- Comunidad de Madrid Grant No. 910729. Another author (N.B.) thanks a postdoctoral fellowship by Spanish MEC under the program "Estancias de jóvenes doctores y tecnólogos extranjeros en España". One of the authors (F.J.A.) thanks the financial support by the programme of "Sabáticos Complutenses" of the Universidad Complutense de Madrid. The EQM calculations were performed on a NEC-SX5 vector supercomputer, through a grant from the "Institut du Développement des Ressources en Informatique Scientifique" (IDRIS-CNRS) in Orsay (France).Peer reviewe