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 Title: AB INITIO CALCULATION APPLIED TO THE STUDY OF ORGANIC NON-RIGID MOLECULES WITH (AT LEAST) THREE INTERACTING TORSIONS. Author(s): Senent, Maria Luisa S Subject(s): Mini-symposium: Large Amplitude Motions Abstract: I present new methodology for the spectroscopic study at very low temperatures of non-rigid organic moleculesdetected in star formation regions of the interstellar medium. As examples of these studies, recent relevant results are shown. The last works on ethylen glycol (EGLY)and on the $C_3 O_6 H_6~$ isomers are detailed. The firts species, ethylen glycol, was astrophysically identified in 2002. Many medium-sized organic molecules present non-rigidity. Torsional motions and, in general, large amplitude motions, intertransform the different conformers that can stabilize by the formation of intramolecular hydrogen bonds. In the low energy regions of the potential energy surface, these hydrogen bonds can determine the symmetry and they can play important roles on the structure and on the low vibrational energy levels. A variational procedure of reduced dimensionality based on CCSD(T)-F12 calculations is applied to understand the far infrared spectrum of cis-gauche-EGLY [1] where three interacting internal rotations intertransform all the minima. The anisotropy of the surface in the gauche region converts the assignment and classification of the torsional levels into a tricky puzzler. The effects of the isotopic substitutions on the spectra are also analysed. Preliminary results for the $C_3 O_6 H_6~$ species obtained using the new the procedure, are shown. Issue Date: 22-Jun-20 Publisher: International Symposium on Molecular Spectroscopy Citation Info: APS Genre: CONFERENCE PAPER/PRESENTATION Type: Text Language: English URI: http://hdl.handle.net/2142/107661 Date Available in IDEALS: 2020-06-26
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