An experimental and theoretical study of the dissociative ionization of CCl₄, CHCl₃ and CH₂Cl₂ by an intense laser field

Abstract

The dissociative ionization of polyatomic molecules CCl₄ (tetrachloromethane), CHCl₃ (trichloromethane) and CH₂Cl₂ (dichloromethane) by intense, 532 nm, 35 ps, 10^L3 W cm^-2 linearly polarized, laser fields is explored. The laser-induced fragmentation pattern is found to be substantially different from that obtained using 70 eV electrons. Attempts are made to rationalize these differences in terms of distortions of the molecular electron density distributions caused by the intense laser field. Such distorted charge-cloud distributions are computed in an approximate fashion by ab initio quantum-chemical techniques. Angular distributions of various fragment ions have also been measured. A pronounced anisotropy is exhibited in many (but not all) cases, with the ion signal being detected mainly along the direction of the laser's polarization axis.