Kinetic Isotope Effects on the Photolysis of C₆₀H₁₈ and C₆₀D₁₈

Abstract

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 245 nm from a low pressure mercury lamp under He. It was found that at 212 nm the photolysis rate constant of C₆₀H₁₈ molecule ^Hk₂₁₂  =  8.68 × 10⁻⁴ s⁻¹ was significantly higher than that of its deuterated analogous C₆₀D₁₈: ^Dk₂₁₂  =  5.93 × 10⁻⁴ s⁻¹. Similarly, at 256 nm it was confirmed the result that C₆₀D₁₈ was photolyzed more slowly than C₆₀H₁₈. Also in this case, ^Hk₂₅₆  =  6.83 × 10⁻⁴ s⁻¹ is significantly higher than that of its deuterated analogous C₆₀D₁₈: ^Dk₂₁₂  =  3.74 × 10⁻⁴ s⁻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 C_3ν 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 C_3ν ‐ 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 C_3ν ‐C₆₀H₁₈ is k₂₁₇  =  4.04 × 10⁻⁴ s⁻¹ and k₂₅₅  =  2.25 × 10⁻⁴ s⁻¹.

Keywords:

• C₆₀H₁₈
• Decomposition kinetics
• Fullerene
• Photolysis
• Photolysis rate constant
• UV irradiation

ACKNOWLEDGMENTS

The present research has been supported by grant AYA2007‐64748 of the Spanish Ministerio de Ciencia e Innovacion. Many thanks to Alexandr Talyzin from the Department of Experimental Physics Umeå University, Sweden, for the donation of a sample of C₆₀H₁₈ prepared under high hydrogen pressure.