64 research outputs found
Collisional excitation of water by hydrogen atoms
We present quantum dynamical calculations that describe the rotational
excitation of HO due to collisions with H atoms. We used a recent, high
accuracy potential energy surface, and solved the collisional dynamics with the
close-coupling formalism, for total energies up to 12 000 cm. From these
calculations, we obtained collisional rate coefficients for the first 45 energy
levels of both ortho- and para-HO and for temperatures in the range T =
5-1500 K. These rate coefficients are subsequently compared to the values
previously published for the HO / He and HO / H collisional
systems. It is shown that no simple relation exists between the three systems
and that specific calculations are thus mandatory
Hyperfine collisional excitation of ammonia by molecular hydrogen
Ammonia is one of the most widely observed molecules in space, and many
observations are able to resolve the hyperfine structure due to the electric
quadrupole moment of the nitrogen nucleus. The observed spectra often display
anomalies in the satellite components of the lines, which indicate substantial
deviations from the local thermodynamic equilibrium. The interpretation of the
spectra thus requires the knowledge of the rate coefficients for the hyperfine
excitation of NH induced by collisions with H molecules, the dominant
collider in the cold interstellar medium. In this paper we present the first
such calculations using a recoupling approach. The rate coefficients are
obtained for all hyperfine levels within rotation-inversion levels up to
and temperatures up to 100 K by means of quantum scattering close-coupling
calculations on an accurate, five-dimensional, potential energy surface. We
show that the rate coefficients depart significantly from those obtained with
the statistical approach and that they do not conform to any simple propensity
rules. Finally, we perform radiative transfer calculations to illustrate the
impact of our new rate coefficients by modelling the hyperfine line intensities
of the inversion transition in ground state para-NH () and of the
rotational transition in ortho-NH
Collisional Excitation and Non-LTE Modeling of Interstellar Chiral Propylene Oxide
The first set of theoretical rotational cross sections for propylene oxide (CH3CHCH2O) colliding with cold He atoms has been obtained at the full quantum level using a high-accuracy potential energy surface. By scaling the collision reduced mass, rotational rate coefficients for collisions with para-H2 are deduced in the temperature range 5-30 K. These collisional coefficients are combined with radiative data in a non-LTE radiative transfer model in order to reproduce observations of propylene oxide made toward the Sagittarius B2(N) molecular cloud with the Green Bank and Parkes radio telescopes. The three detected absorption lines are found to probe the cold (∼10 K) and translucent (nH ∼2000 cm-3) gas in the outer edges of the extended Sgr B2(N) envelope. The derived column density for propylene oxide is Ntot ∼3 x 1012 cm-2, corresponding to a fractional abundance relative to total hydrogen of ∼2.5 x 10-11. The present results are expected to help our understanding of the chemistry of propylene oxide, including a potential enantiomeric excess, in the cold interstellar medium
Collisional Excitation and Non-LTE Modeling of Interstellar Chiral Propylene Oxide
The first set of theoretical rotational cross sections for propylene oxide (CH3CHCH2O) colliding with cold He atoms has been obtained at the full quantum level using a high-accuracy potential energy surface. By scaling the collision reduced mass, rotational rate coefficients for collisions with para-H2 are deduced in the temperature range 5-30 K. These collisional coefficients are combined with radiative data in a non-LTE radiative transfer model in order to reproduce observations of propylene oxide made toward the Sagittarius B2(N) molecular cloud with the Green Bank and Parkes radio telescopes. The three detected absorption lines are found to probe the cold (∼10 K) and translucent (nH ∼2000 cm-3) gas in the outer edges of the extended Sgr B2(N) envelope. The derived column density for propylene oxide is N tot ∼3 x 1012 cm-2, corresponding to a fractional abundance relative to total hydrogen of ∼2.5 x 10-11. The present results are expected to help our understanding of the chemistry of propylene oxide, including a potential enantiomeric excess, in the cold interstellar medium
The Bioperl toolkit: Perl modules for the life sciences
The Bioperl project is an international open-source collaboration of biologists, bioinformaticians, and computer scientists that has evolved over the past 7 yr into the most comprehensive library of Perl modules available for managing and manipulating life-science information. Bioperl provides an easy-to-use, stable, and consistent programming interface for bioinformatics application programmers. The Bioperl modules have been successfully and repeatedly used to reduce otherwise complex tasks to only a few lines of code. The Bioperl object model has been proven to be flexible enough to support enterprise-level applications such as EnsEMBL, while maintaining an easy learning curve for novice Perl programmers. Bioperl is capable of executing analyses and processing results from programs such as BLAST, ClustalW, or the EMBOSS suite. Interoperation with modules written in Python and Java is supported through the evolving BioCORBA bridge. Bioperl provides access to data stores such as GenBank and SwissProt via a flexible series of sequence input/output modules, and to the emerging common sequence data storage format of the Open Bioinformatics Database Access project. This study describes the overall architecture of the toolkit, the problem domains that it addresses, and gives specific examples of how the toolkit can be used to solve common life-sciences problems. We conclude with a discussion of how the open-source nature of the project has contributed to the development effort
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
The state dependence of the interaction of metastable rare gas atoms Rg*(ms3 P 2,3 P 0) (Rg=Ne, Ar, Kr, Xe) with ground state sodium atoms
Collisional excitation of CH2 rotational/fine-structure levels by helium
International audienc
- …