TopModel

TopModel aims at investigating one of the pending question in the field of high resolution molecular spectroscopy in the gas phase: how to model, as accurately as possible, the fingerprint signature of torsional motion(s) in a molecule containing one or several chemical groups undergoing a large amplitude motion. The necessity to answer the question is closely related to the incoming need to observe and characterize the (sub)-millimeter signature of astrophysical and pre-biotic molecules (mainly organic molecules weighting less than 500 amu) containing CH3 rotors, OH, or amino groups. As an application, these molecules are among the new targets that are particularly targeted in the future observations of the radiotelescopes HERSCHEL (Spatial Observatory), ALMA (Atacama Large Millimeter Array) and SOFIA (Stratospheric Observatory for Infrared Astronomy). The PhLAM and LISA laboratories will share their expertise in the field of molecular spectroscopy to be competitive at an international level on both experimental and theoretical challenges. On the experimental side, the project aims at recording the spectral signature of selected targets in the 0.001-2 Thz range using the microwave, millimetre and sub-millimeters PhLAM sources, to be partly updated, and the newly developed Jet-AILES supersonic jet (PhLAM-LADIR-PALMS consortium) to be implemented on the IRTF spectrometer of the AILES beam line (RS Soleil), to benefit of its high expected brilliance in the Thz range. On the theoretical side, the project aims at addressing several important issues related to non-rigidity effects in molecules displaying internal motions of one or several CH3, OH or amino groups. Specifically, internal rotation in molecules with one such group will be examined in the case when the molecule under consideration displays several conformations, or to the description of highly excited torsion-rotation states. Internal rotation in a molecule with two non-equivalent such groups will also be considered. In both cases, the tunneling pattern and the coupling of the large amplitude motion(s) with the overall rotation will be investigated. Target molecules are key astrophysical molecules like ethanol, methyl formate, acetamide, and terpenes. Quantum chemical calculations will be used to predict molecular structures as well as barrier heights. Computer programs will be written and used for the interpretation of the unprecedented high sensitivity and high resolution spectra which will be reach for the first time in a very large spectral domain (from MW to several THz) by the new radio-telescopes mentioned. It is a fundamental research project in physical chemistry with as applications astrophysical or atmospheric databases.