Studies On Dissociative Ionization And Coulomb Explosion Of Halogenated Methane Irradiated By Femtosecond Laser Field

Numerous researches on interaction between molecules and intense laser field have been carried out with the development of ultra-fast intense femtosecond laser technology. Profiting from the ultra-high peak power of the femtosecond laser, many new phenomena have been observed, such as multi-photon dissociative ionization, above threshold ionization, double ionization, field ionization and coulomb explosion. Photolysis of halogenated methane is a hot research area in atmospheric chemistry because the energetic halogen atoms resulting from photolysis of halogenated methane can badly demage the ozonosphere. Moreover, halogenated methane is the simplest halogenated hydrocarbon. It has also become a benchmark for the photoionization and photodissociation of polyatomic molecule because of its relative less atoms. In this paper, we have studied the photoionization, photodissociation and coulomb explosion of halogenated methane in an800nm,1013-1014W/cm2femtosecond laser field with our homebuilt DC sliced imaging system. The specific work is as follows:1. The multi-photon dissociative ionization and coulomb explosion of CH3CI in an800nm femtosecond laser field have been investigated. Special coulomb explosion channel with H3+ejection has been observed. The anisotropy dependency of H3+on the laser intensity is also well discussed and compared with that of the35C1+ejection channel. The competition between the H3+and35C1+ejection processes has been investigated at different laser intensities, and sequential and non-sequential double ionization are found to be responsible for the dependencies of their ion yields on laser intensity.2. The multi-photon dissociative ionization and coulomb explosion of CH2XY (X=C1, Y=Cl, Br, I) in an800nm femtosecond laser field have been investigated. Preferred bond scission between C-X and C-Y bond in multi-photon dissociative ionization and coulomb explosion has been dissicussed. Furthermore, the influence of substituent Y atom on the-competition between cleavage of C-X and C-Y bond is also investigated both in multi-photon dissociative ionization and coulomb explosion.3. The multi-photon dissociative ionization and coulomb explosion of CHCl3and CCl4in an800nm femtosecond laser field have been investigated. Numerous multi-body dissociation and coulomb explosion channels of CHCl3and CCl4have been observed. It is also found that the ion yields of secondary dissociation channels of these two multiple halogenated methanes are very high.