THERMAL-STABILITY OF FULLERENES - A SHOCK-TUBE STUDY ON THE PYROLYSISOF C-60 AND C-70

The thermal stability of fullerenes C-60 and C-70 dispersed in Ar was studied behind shock waves by following the time-dependent absorption and emission of the proposed decomposition product C-2. The gas-partic le mixtures filled into the shock tube were heated to temperatures 239 0 K less than or equal to T less than or equal to 3450 K at pressures of 1.1 bar less than or similar to p less than or equal to 2.1 bar. Be cause of the relatively high vapour pressure of the fullerenes, they e vaporate in a few microseconds so that both Cao and C-70 are in the ga s phase during most of the observation time. C-2 concentration profile s were measured by a ring dye laser spectrometer at v = 21 393.12 cm(- 1). Simultaneously, the time behaviour of spectrally resolved light em itted from the shock-heated aerosol was recorded by an intensified CCD camera. A simplified reaction mechanism with both Ca formation and co nsumption reactions was proposed and the experimental results were dis cussed in terms of kinetic parameters. Rate coefficients k(1) and k(2) of the initial pyrolysis reactions (R1) and (R2) C-60 --> C-2 + C-58 (R1) k(1) = 4.0 x 10(12) exp(-515 kJ/molRT)s(-1) C-70 --> C-2 + C-68 ( R2) k(2) = 1.4 x 10(11) exp(-414 kJ/mol/RT)(s-1) were determined. Two different models for the further decomposition of fullerene fragments were discussed and compared with computer simulations.