Abstract

All molecules having equivalent identical nuclei with non-zero spin occur in different spin modifications (for example ortho and para H₂). As is well known, the or-tho-para conversion in gaseous H₂ is extremely slow. For nuclear spin modifications of larger molecules, like CH₃F, conversion times are also believed to be very long. Until recently this could not be verified experimentally since no separation method for polyatomic molecules existed. Laser technique based on Light Induced Drift (LID) opened up new possibilities in this field, providing an efficient way to separate nuclear spin modifications. This can be seen as follows. Since certain spin states combine with certain rotational states only, different nuclear spin species can be spectroscopically distinguished (see Fig. 1 as an example). Moreover, since the kinetic cross section changes upon excitation, the two species can now be separated by means of LID.¹

© 1994 IEEE