Presentation on theme: "The microwave spectrum of partially deuterated species of dimethyl ether D. Lauvergnat, a L. Margulès, b R. A. Motyenko, b J.-C. Guillemin, c and L. H."— Presentation transcript:
The microwave spectrum of partially deuterated species of dimethyl ether D. Lauvergnat, a L. Margulès, b R. A. Motyenko, b J.-C. Guillemin, c and L. H. Coudert d a LCP, CNRS/Université Paris-Sud, Orsay, France b PhLAM, CNRS/Université des Sciences et Technologies de Lille 1 Villeneuve d'Ascq, France c Sciences Chimiques de Rennes, Rennes, France d LISA, CNRS/Universités Paris Est et Denis Diderot, Créteil, France
Why are we interested in deuterated species? A large number of unidentified lines in the ISM may be due to partially deuterated species. Measuring partially deuterated species provides astronomers with a tool to measure the [D]/[H] ratio. In this talk the microwave spectrum of the partially deuterated species of dimethyl ether CH 2 DOCH 3 will be investigated theoretically.
Outline Torsional energy levels of the normal species Torsional energy levels of the deuterated species Torsional Hamiltonian Potential energy surface Torsional functions Nature of the torsional energy levels Microwave spectrum of the deuterated species
Torsional coordinates The torsional angles 1 and 2 are used
PES of the normal species with: 1. Durig, Li, and Groner, JMS 62 (1976) 159. 2. MP2 with cc-PVTZ basis set.
Torsional energy levels: normal species 4 tunneling sublevels G 36
Torsional function: normal species ( 1, 2 ) A 1 sublevel
What happens when the molecule is deuterated? The kinetic energy part of the torsional Hamiltonian is modified because of the mass change. The effective potential energy function for the torsion is changed due to zero-point energy effects.
Torsional energy levels: deuterated species 9 tunneling sublevels 3 nondegenerate 3 doubly degenerate
Torsional function of the 1 st A-type sublevel D-in plane
Torsional function of the 2 nd A-type sublevel D-out of plane
Torsional function of the 3 rd A-type sublevel D-out of plane
Torsional energy levels D-in plane Torsional function centered around Internal rotation of the other methyl group D-out of plane Tunneling between and Internal rotation of the other methyl group
The microwave spectrum Two sets of transitions. Set I Set II
The next steps Overall rotation will be taken into account. Rotational dependence of the various tunneling splittings will be determined using the water dimer formalism. 1 The energy difference between the two sublevel sets should be calculated accurately. We can begin analyzing the microwave spectrum. 1. Hougen, JMS 114 (1985) 395 and Coudert and Hougen, JMS 139 (1990) 259.
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