title: Nuclear Spin Conversion in CH4: A Multichannel Relaxation Mechanism.
abstract: Experiments on nuclear spin interconversion of ortho, para, and meta nuclear spin isomers of the methane molecule have been undertaken in gas phase and cryomatrices. Only the latter environment has led to the observation of the nuclear spin conversion. In this study, a quantitative explanation is given for the first time by considering the coupling of three relaxation paths: meta ⇔ para, meta ⇔ ortho, and ortho ⇔ para. The global evolution of the three populations of spin isomers is thus described by two characteristic times, which have been calculated using the best values of the energy levels for the vibrational ground state, of the intramolecular magnetic interactions, and of the collisional relaxation rates, and for different pressure and temperature conditions. Such calculations also provide an indication for the proper choice of reliable scenarios for experimental separation of the spin isomers of methane.
authors.affiliation: Univ. Lille , CNRS, UMR 8523 - PhLAM - Physique des Lasers Atomes et Molécules, F-59000 Lille, France.
authors.forename: Patrice
authors.initials: P
authors.lastname: Cacciani
authors.affiliation: Univ. Lille , CNRS, UMR 8523 - PhLAM - Physique des Lasers Atomes et Molécules, F-59000 Lille, France.
authors.forename: Jean
authors.initials: J
authors.lastname: Cosléou
authors.affiliation: Univ. Lille , CNRS, UMR 8523 - PhLAM - Physique des Lasers Atomes et Molécules, F-59000 Lille, France.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Khelkhal
authors.affiliation: Department of Experimental Physics, Faculty of Mathematics, Physics and Informatics, Comenius University , Mlynská dolina, 842 48 Bratislava, Slovakia.
authors.forename: Peter
authors.initials: P
authors.lastname: Čermák
authors.affiliation: Dipartimento di Chimica "Giacomo Ciamician", Università di Bologna , via Selmi 2, 40126 Bologna, Italy.
authors.forename: Cristina
authors.initials: C
authors.lastname: Puzzarini