101 research outputs found
A new ab initio potential energy surface for the collisional excitation of N2H(+) by H2
10 pags.; 14 figs.© 2015 AIP Publishing LLC. 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+âH2 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 â2530 cmâ1. 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 âadiabatic-hindered-rotorâ 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 calculationsThis research was supported by the CNRS national program
âPhysique et Chimie du Milieu Interstellaire.â F.L. and
Y.K. also thank the Agence Nationale de la Recherche
(ANR-HYDRIDES), contract No. ANR-12-BS05-0011-01.
We acknowledge Laurent Pagani for stimulating this work.Peer Reviewe
The radiative lifetime of metastable CO ()
We present a combined experimental and theoretical study on the radiative
lifetime of CO in the state. CO molecules in a beam are
prepared in selected rotational levels of this metastable state,
Stark-decelerated and electrostatically trapped. From the phosphorescence decay
in the trap, the radiative lifetime is measured to be ms for the
level. From spin-orbit coupling between the and
the state a 20% longer radiative lifetime of 3.16 ms is calculated for
this level. It is concluded that coupling to other states contributes
to the observed phosphorescence rate of metastable CO.Comment: replaced with final version, added journal referenc
On inelastic hydrogen atom collisions in stellar atmospheres
The influence of inelastic hydrogen atom collisions on non-LTE spectral line
formation has been, and remains to be, a significant source of uncertainty for
stellar abundance analyses, due to the difficulty in obtaining accurate data
for low-energy atomic collisions either experimentally or theoretically. For
lack of a better alternative, the classical "Drawin formula" is often used.
Over recent decades, our understanding of these collisions has improved
markedly, predominantly through a number of detailed quantum mechanical
calculations. In this paper, the Drawin formula is compared with the quantum
mechanical calculations both in terms of the underlying physics and the
resulting rate coefficients. It is shown that the Drawin formula does not
contain the essential physics behind direct excitation by H atom collisions,
the important physical mechanism being quantum mechanical in character.
Quantitatively, the Drawin formula compares poorly with the results of the
available quantum mechanical calculations, usually significantly overestimating
the collision rates by amounts that vary markedly between transitions.Comment: 9 pages, 6 figures, accepted for A&
Molecular excitation in the Interstellar Medium: recent advances in collisional, radiative and chemical processes
We review the different excitation processes in the interstellar mediumComment: Accepted in Chem. Re
BASECOL2012: A collisional database repository and web service within the Virtual Atomic and Molecular Data Centre (VAMDC)
The BASECOL2012 database is a repository of collisional data and a web service within the Virtual Atomic and Molecular Data Centre (VAMDC, http://www.vamdc.eu). It contains rate coefficients for the collisional excitation of rotational, ro-vibrational, vibrational, fine, and hyperfine levels of molecules by atoms, molecules, and electrons, as well as fine-structure excitation of some atoms that are relevant to interstellar and circumstellar astrophysical applications. Submissions of new published collisional rate coefficients sets are welcome, and they will be critically evaluated before inclusion in the database. In addition, BASECOL2012 provides spectroscopic data queried dynamically from various spectroscopic databases using the VAMDC technology. These spectroscopic data are conveniently matched to the in-house collisional excitation rate coefficients using the SPECTCOL sofware package (http:// vamdc.eu/software), and the combined sets of data can be downloaded from the BASECOL2012 website. As a partner of the VAMDC, BASECOL2012 is accessible from the general VAMDC portal (http://portal.vamdc.eu) and from user tools such as SPECTCOL
Ro-vibrational excitation of CS by He
International audienc
Rotational excitation of carbon monosulfide by collisions with helium
International audienc
Relaxation of diatomic molecules by isotropic collisions: application to depolarizing collisions of CS by He atoms
International audienc
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