Eur. Phys. J. D 22, 199-207 (2003)
https://doi.org/10.1140/epjd/e2003-00013-1

Experimental determination of spin-rotation and spin-spin magnetic interactions in ¹³CH₃F by nuclear spin conversion

Laboratoire de Physique des Lasers, Atomes et Molécules, CERLA, Centre Lasers et Applications, Université des Sciences et Technologies de Lille, 59655 Villeneuve d'Ascq Cedex, France

Corresponding author: ^a Patrice.Cacciani@univ-lille1.fr

Received: 23 May 2002
Revised: 18 September 2002
Published online: 21 January 2003

Abstract

When a gas sample of ¹³CH₃F is prepared with a population of isomers (ortho and para forms) far from the equilibrium given by nuclear spin statistics, it relaxes towards this equilibrium with an exponential decay rate. This phenomenon called nuclear spin conversion is mainly governed by intramolecular spin-spin and spin-rotation interactions. In the quantum relaxation model [P.L. Chapovsky, Phys. Rev. A 43, 3624 (1991)], two pairs of ortho-para levels (J=9, K=3; J'=11, K'=1) and (J=20, K=3; J'=21, K'=1) are principally responsible for the conversion. The levels of the second pair are coupled by both spin-spin and spin-rotation interactions. The application of an electric field (up to 10 kV/cm) induces a crossing of the Stark components of this pair, which is observed for the first time. A specific experimental set-up based on an electric field of alternating triangular shape is used, which allows the determination of the strength of both interactions via the measurement of the spin conversion decay rates. This work yields the first experimental value for the electronic contribution to the spin-rotation interaction in ¹³CH₃F.