Untitled - Laboratoire d'Astrophysique de l'Observatoire de Grenoble

Table shows not only the volume of the observational activity, but also the trend in the use of the telescopes. It
is worth noting the positive gradient in the use of the CSO and JCMT submillimeter bands, and the net increase
of the use of the IRAM interferometer PdB. Both trends shows how very naturally Astromol is preparing itself
at the best exploitation of the two future big international projects: Herschel and ALMA.
2.3 Development of astrophysical models
Two classes of models have been developed within the Astromol team:
i) Radiative transfer models (CC) that compute the line emission from the collapsing envelopes, for several
molecules (H2O, CO : Ceccarelli et al. 1996, 2003; CH3OH : Maret et al. 2005; SO and SO2 : Wakelam
et al. in prep; HDO : Parise et al. 2005). Astromol (CC, BL) also developed a simple LVG code for the
first level of analysis in more general conditions (like for example outflows). Some results of these models
are made publicly available at the WEB site:
http://www-laog.obs.ujf-grenoble.fr/∼ceccarel/mepew/mepew.html.
ii) Chemical models of star forming regions (CC). We have developed codes specialized in the Sulphur chem-
istry (Wakelam et al. 2004, 2005), in the molecular deuteration due to grain surface (Parise et al. 2005),
and deuterium chemistry of the ion H + 3 in protostellar disks (Ceccarelli & Dominik 2005).
In addition, Astromol members (LW, AF, CC, BL, PV) have undertaken recently a systematic theoretical and
observational survey of the cyanopolyyne family of rod-like molecules, of general formula HC2n+1N. It should
serve as a prelude to several new lines of observations and theories for larger molecules (notably organic complex
molecules) in several types of astrophysical environments.
2.4 Molecular physics: theories and codes
Several classes of new theoretical and algorithmic tools to solve molecular physics problems relevant to astrophysics
are currently developed and used in the Astromol team. They can be regrouped in the following
classes:
i) A quantum chemistry code that takes into account explicitely the correlation cusp between each electron
pair. The fulfillment of this mathematical condition permits to approach the infinite basis set limit at the
coupled cluster level of theory and to achieve an accuracy in the cm −1 range for the interaction of small
non-reactive molecules.
ii) A generalization of the so-called Transition State Theory for inelastic processes. This new method provides
a geometrical view of the problem, and it promises to simplify the computation of the molecular collisional
cross-sections.
iii) A new strategy for computing inter-molecular potential surfaces which includes the intra-molecular motion
(i.e. the motion of the nuclei in each interacting molecule). The problem here is the sampling of the
surface, which has several dimensions (≥ 4). For this, we implemented an optimized sampling, based on
the high-accuracy vibrational wavefunctions.
iv) A new strategy for computing inter-molecular potential surfaces of long rod-like molecules, like HC3N with
He or H2. In these systems, the surface is highly anysotropic and, therefore, the fitting in the angular
coordinates is particularly difficult, and this is known as “steric hindrance problem”.
v) A quasi-classical scattering code, based on a canonical Monte-Carlo strategy, to directly compute the
collisional rates (with no need to integrate the cross-sections over the Boltzman velocity distribution).
The computations briefly described above are very CPU-time consuming and require a large amount of time of
high-performance computers, like the IDRIS and CINES supercomputers. For this reason, Astromol members
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