15min:

Z.-D. SUN, Department of Physics, Toyama University, 930-8555, Japan;; K. TAKAGI, S. YAMADA, H. TANAKA AND F. MATSUSHIMA, Department of Physics, Yantai University, 264005, P. R. China.

The separation and conversion of nuclear spin isomers with A_g, B_1g, B_2u, and B_3u symmetry of normal ethylene (C₂H₄) have been investigated by a newly assembled experimental setup in the first case studied so far for a planar, asymmetric-top polyatomic molecule that has four nuclear spin isomers with the D_2h symmetry group. One of the nuclear spin isomers of C₂H₄ is first separated using the 10P44 CO₂ laser line in the method of Light-Induced Drift\footnoteF.Kh.~Gelmukhanov, and A.M.~shalagin, JETP~Lett. 29, 711 (1979).. The equilibration decay curves of the spin isomers are then measured using a second probe CO₂ laser to monitor absorption spectral line intensities as a function of time. The conversion rates between isomers have been determined by fitting these decay curves to an exponential function. The experimental results and their interpretations will be presented.