Studies on photodissociation of dibromoalkane in UV region

The photodissociation of CH2Br2, 1,2-C2H4Br2 and 1,4-C4H8Br2 near 234 and 267 nm has been studied using resonance-enhanced multiphoton ionization with time-of-flight mass spectrometry. The wavelength dependence of the relative quantum yields ΦBr and ΦBr∗ for both Br(2P3/20) and Br∗(2P1/20) channels was measured. The results indicated that the yields ΦBr of C2H4Br2 is larger than that of CH2Br2. And the quantum yields wavelength dependent of C4H8Br2 shows a different tendency compared to CH2Br2 and C2H4Br2. A likely explanation for the different quantum yields relies on the non-adiabatic transitions and avoided curve crossing mechanism. Additionally, ab initio calculations were performed to get potential energy surface curves of CH2Br2 to elucidate the photodissociation channels in UV region.