Dissociation of methane in intense laser fields

The dissociation of methane in the intense laser field has been investigated experimentally and theoretically. Using an amplified ultrafast Ti:sapphire laser around 800 nm coupled to a TOF mass spectrometer, all the primary and secondary ions were produced and detected at the laser intensities 10(13) to 10(14) W/cm(2). The experimental results show that the dissociation of methane proceeds via a stepwise mechanism by gradually increasing, the laser intensity. The maximum HI yield is formed when the linearly polarized laser field is parallel to the axis of the TOF tube. A quasi-diatomic theoretical model has been proposed and used to interpret the dissociation of polyatomic molecules. The model assumes that only the dissociative bond is considered and the rest of the molecular geometry is fixed during the dissociation. For each step, the profiles of the dressed potential energy surfaces (PESs) along the dissociative bond of the molecule at different laser intensities are calculated. Quasi-classical trajectories on the dressed PESs are calculated, showing that the wave packet is modulated by the sinusoidal laser field. Theoretical dissociation probabilities are thus calculated. The results can fully interpret the overall dissociation processes and the angular dependence of H+ yield.