Laser-induced trapping of chlorine molecules with pico- and femtosecond pulses

We have studied the multielectron dissociative ionization of Cl₂ with intense 130-fs laser pulses at 395, 610, and 790 nm, and 2-ps pulses at 610 nm. The kinetic-energy releases and the fragmentation branching ratios are found to be essentially independent of the laser wavelength and of the pulse duration. Moreover, for all fragmentation channels up to Cl₂⁸⁺→Cl⁴⁺+Cl⁴⁺, the measured energy releases are systematically 70% of those expected from a simple Coulomb explosion of the molecule at its neutral ground-state equilibrium internuclear distance. This constant-energy ratio is even more surprising in the picosecond regime, where the pulse duration largely exceeds the molecular ground-state vibrational period by a factor of 30 so that the molecular motions cannot be considered as frozen during interaction. The results are tentatively explained in terms of laser-induced stabilization of the transient molecular species via charge-resonance or charge-transfer couplings. In this picture, the electron removal occurs at the end of the laser pulse, leading only then to the explosion of the multicharged ions.