HIGH-TEMPERATURE FLASH PYROLYSIS OF DI-TE RT-BUTYL PEROXIDE IN A JET-COOLED EXPANSION

The mass distribution and time-of-flight (TOF) spectra for the pyrolyt ic fragments of di-tert-butyl peroxide (DTBP) seeded in He or Ar carri er gas have been achieved by using time-resolved mass spectrometric an d high temperature flash pyrolysis techniques. The dependence of DTBP conversion yield on the heated SiC tube temperature (T-s) shows that t he precursor molecule in the carrier gas starts to decompose obviously at 900 K, and reaches complete decomposition at 1 300 K. Two major fr agments CH3COCH3 and CH3 . radical are observed. In a pulsed free jet expansion of 4% mole fraction of DTBP/Ar gas mixture, the TOF spectra of pyrolytic fragments measured at T-s=1 000 K show that there are two peaks for CH3COCH3+ ion (m/e=58) and its fragment ions, CH3CO+ and CH 3+ (m/e=43 and 15). When He or N-2 is used as a carrier gas, however, only one peak is observed in its TOF spectra. This result implies that a fraction of jet-cooled CH3COCH3 (m/e=58) molecules combine with Ar and form the van der Waals molecules CH3COCH3 . Ar-n. Formation of CH3 COCH3 . Ar-n is also suggested via the TOF experiments in which aceton e is used as a precursor seeded in Ar carrier gas. The proposed mechan ism of DTBP flash pyrolysis mainly involves the initial split of the O -O bond of DTBP to generate (CH3)(3)CO . radical, followed by the deco mposition of this radical into CH3COCH3 and CH3 . radical, and the rec ombination or secondary bi-molecular reactions of product radicals are suppressed in the flash pyrolysis of DTBP with a very shot contact ti me.