Kinetic Isotope Effects on the Photolysis of C60H18 and C60D18

Fullerane C60H18 and its deuterated analogous C60D18 were synthesized in n-hexane solution by a reduction reaction of C60 under the action of HCl or DCl on Zn dust. The resulting solutions were subjected to UV irradiation at 245nm from a low pressure mercury lamp under He. It was found that at 212nm the photolysis rate constant of C60H18 molecule Hk212 = 8.68 x 10-4s-1 was significantly higher than that of its deuterated analogous C60D18: Dk212 = 5.93 x 10-4s-1. Similarly, at 256nm it was confirmed the result that C60D18 was photolyzed more slowly than C60H18. Also in this case, Hk256 = 6.83 x 10-4s-1 is significantly higher than that of its deuterated analogous C60D18: Dk212 = 3.74 x 10-4s-1. Kinetic isotope effect involving the C-H and C-D bond activation has been advocated to explain the differences in photodecomposition speed of C60H18 in comparison to C60D18. On the basis of solubility in alkanes and unique electronic absorption spectrum C60H18 with C3 symmetry prepared under high hydrogen pressure can be easily distinguished from the C60H18 and its deuterated analogous C60D18 synthesized in n-hexane from Zn/HCl or Zn/DCl. The C3 - C60H18 displayed also a different evolution of the electronic absorption spectrum under photolysis in comparison to C60H18 and its deuterated analogous C60D18. The pseudofirst rate constant of C3 -C60H18 is k217 = 4.04 x 10-4s-1 and k255 = 2.25 x 10-4s-1.