Abstract book - Prof. Per Jensen, Ph.D. - Bergische Universität ...

Poster session, H26 139Nuclear Spin Conversion in MethanePatrice Cacciani 1 , Peter Čermak 1 , Jean Cosléou 1 , Mohamed Khelkhal 1 , CristinaPuzzarini 21 Laboratoire de Physique des Lasers, Atomes et Molécules, UMR CNRS 8523,Université Lille 1 Sciences et Technologies, 59655 Villeneuve d'Ascq Cedex, France,Patrice.Cacciani@univ-lille1.fr; 2 Dipartimento di Chimica "G. Ciamician", Universita' diBologna, Via F. Selmi, 2 40126 Bologna, Italy, cristina.puzzarini@unibo.itCacciani P.Cermak P.Cosleau J.Khelkhal M.Puzzarini C.Molecules having equivalent atoms with non zero nuclear spin exist as isomers, whichdiffer by the value I of the total nuclear spin of these atoms. For example, CH 4 is ofmeta (I = 2), ortho (I = 1) or para (I = 0) species. The well known consequence of thespin modifications is the intensity alternation of rovibrational lines.The mechanism of conversion from one CH 4 spin modification to another has beenstudied in the framework of the Quantum Relaxation Model 1 . This model shows thatnuclear spin conversion is governed by intramolecular spin-spin and spin-rotationmagnetic interactions and by collisions. Interactions couple energetically closed levelsof different spin symmetry, for example ortho and para levels, and this mixing isinterrupted by a collision that makes the molecule leave the mixed state and puts it in apure state, for example ortho or para, with a non zero probability for both modifications.Calculations have been performed with :• new relevant ab initio spin-spin and spin rotation parameters,• identification of ortho and para interacting levels,• ground state line broadening parameters,Spin conversion rates have been estimated for different environments.References[1] P. L. Chapovsky, Phys. Rev. A, 43, 3624, 1991