CCl2(Ã 1B1) radical formation in VUV photolyses of CCl4 and CBrCl3

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Abstract
In vacuum ultraviolet photolyses of CCl4 and CBrCl3 a diffuse emission band was observed in the region of 410–750 nm by Ar i resonance and H Lyman‐α line irradiation. The band was attributed to a CCl2(Ã 1B1 → X̃ 1A1) transition from the measurements of the appearance energies of the emitters produced from photodissociative excitation of both CCl4 and CBrCl3 using synchrotron radiation. The fluorescence decay of the CCl2(Ã → X̃) transition showed a superposition of two lifetime components of 2.17±0.26 and 4.0±0.12 μs at pressures from 10 to 140 mTorr. The pressure dependence of the amplitudes for the two lifetimes suggests the occurrence of collision‐induced intersystem crossing between 1B1 and 3B1 states of CCl2 radicals. The absorption cross section of CBrCl3 was measured for the first time in the 106–200 nm wavelength region and tentative assignments of Rydberg transitions are presented.