Despite their broad implications for phenomena such as molecular bonding or chemical reac tions, our knowledge of multi electron dynamics is limited and their theoretical modelling remains a most difficult task. From the experimental side, it is highly desirable to study the dynamical evolution and interaction of the electrons over the relevant timescales, which extend into the attosecond regime. Here we use near single cycle laser pulses with well defined electric field evolution to confine the double ionization of argon atoms to a single laser cycle. The measured two electron momentum spectra, which substantially differ from spectra recorded in all previous experiments using longer pulses, allow us to trace the correlated emission of the two electrons on sub femtosecond timescales. The experimental results, which are discussed in terms of a semiclassical model, provide strong constraints for the development of theories and lead us to revise common assumptions about the mechanism that governs double ionization.

Carrier-envelope phase difference effects in the dissociation of the HD+ molecular ion in the field of an intense, linearly polarized, ultrashort laser pulse are studied in the framework of the time-dependent Schrödinger equation. We consider a reduced-dimensionality model in which the nuclei are free to vibrate along the field polarization and the electrons move in two dimensions. The laser has a central wavelength of 790 nm and a pulse length of 10 fs with intensities in the range 6x10(14) to 9x10(14) W/cm(2). We find that the angular distribution of dissociation to p+D and H+d can be controlled by varying the phase difference, generating differences between the dissociation channels of more than a factor of 2. Moreover, the asymmetry is nearly as large for H+2 dissociation.

A technique for storage of fast-ion beams ͑keV͒ using only electrostatic fields is presented. The fast-ion trap is designed like an optical resonator, whose electrode configuration allows for a very large field-free region, easy access into the trap by various probes, a simple ion loading technique, and a broad acceptance range for the initial kinetic energies of the ions. Such a fast-ion storage device opens up many experimental possibilities, a few of which are presented. ͓S1050-2947͑97͒50803-1͔

Roaming mechanisms, involving the brief generation of a neutral atom or molecule that stays in the vicinity before reacting with the remaining atoms of the precursor, are providing valuable insights into previously unexplained chemical reactions. Here, the mechanistic details and femtosecond time-resolved dynamics of H3+ formation from a series of alcohols with varying primary carbon chain lengths are obtained through a combination of strong-field laser excitation studies and ab initio molecular dynamics calculations. For small alcohols, four distinct pathways involving hydrogen migration and H2 roaming prior to H3+ formation are uncovered. Despite the increased number of hydrogens and possible combinations leading to H3+ formation, the yield decreases as the carbon chain length increases. The fundamental mechanistic findings presented here explore the formation of H3+, the most important ion in interstellar chemistry, through H2 roaming occurring in ionic species.

Strong-field laser-matter interactions often lead to exotic chemical reactions. Trihydrogen cation formation from organic molecules is one such case that requires multiple bonds to break and form. We present evidence for the existence of two different reaction pathways for H3 + formation from organic molecules irradiated by a strong-field laser. Assignment of the two pathways was accomplished through analysis of femtosecond time-resolved strong-field ionization and photoion-photoion coincidence measurements carried out on methanol isotopomers, ethylene glycol, and acetone. Ab initio molecular dynamics simulations suggest the formation occurs via two steps: the initial formation of a neutral hydrogen molecule, followed by the abstraction of a proton from the remaining CHOH2+ fragment by the roaming H2 molecule. This reaction has similarities to the H2 + H2 + mechanism leading to formation of H3 + in the universe. These exotic chemical reaction mechanisms, involving roaming H2 molecules, are found to occur in the ~100 fs timescale. Roaming molecule reactions may help to explain unlikely chemical processes, involving dissociation and formation of multiple chemical bonds, occurring under strong laser fields.