The carrier–envelope phase (CEP) dependence of the dissociation of H+2 is studied with special emphasis on the role of the nuclear mass. We find that the total dissociation probability displays a CEP effect that grows with increasing mass, while the difference between dissociating to p+H and H+p displays an effect that shrinks. Insight into the physical processes involved is given by an analytic description that casts CEP effects as interferences between pathways requiring different numbers of photons.

High-order (three-photon or more) above-threshold dissociation (ATD) of H(2)(+) has generally not been observed using 800 nm light. We demonstrate a strong enhancement of its probability using intense 7 fs laser pulses interacting with beams of H(2)(+), HD(+), and D(2)(+) ions. The mechanism invokes a dynamic control of the dissociation pathway. These measurements are supported by theory that additionally reveals, for the first time, an unexpectedly large contribution to ATD from highly excited electronic states.

The temporal evolution of the dissociation probabilities for various vibrational levels of H 2 + is observed in terms of shifts in the kinetic energy release dissociation spectra, induced by linearly chirped intense laser pulses. In contrast to previous observations, in which no dependence on the chirp sign was observed, the energy spectrum reported here shows peak shifts, up for negative chirp and down for positive chirp. For some vibrational levels, dissociation takes place early on in the pulse; hence, care must be taken while interpreting the effect of pulse duration in photodissociation studies. This interpretation is supported by numerical solutions of the time-dependent Schrödinger equation.

In a recent Letter, Manschwetus et al. [Phys. Rev. Lett. 102, 113002 (2009)] reported evidence of electron recapture during strong-field fragmentation of H 2 -explained using a frustrated tunneling ionization model. Unusually, the signature of this process was detection of excited H * atoms. We report here an extensive study of this process in D 2 . Our measurements encompass a study of the pulse duration, intensity, ellipticity, and angular distribution dependence of D * formation. While we find that the mechanism suggested by Manschwetus et al. is consistent with our experimental data, our theoretical work shows that electron recollision excitation cannot be completely ruled out as an alternative mechanism for D * production.

The multiphoton dissociation branching ratios for H 2 + and D 2 + as a function of laser peak intensity and pulse length are investigated by solving the time-dependent Schrödinger equation in the Born-Oppenheimer approximation, neglecting nuclear rotation. An 800 nm laser pulse with peak intensities from 8 ϫ 10 9 W / cm 2 to 10 14 W / cm 2 and pulse lengths from 5 to 7.5 fs is used. We also investigate the viability of identifying zero-, one-, two-, and three-photon processes based only on the nuclear kinetic energy release spectrum, and check these identifications with a rigorous Floquet-like method.

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Synopsis We explore very slow laser-induced dissociation processes of molecular ion beams employing an upgraded coincidence 3D momentum imaging technique. A selection of our studies, focused on zero-photon dissociation of H 2 + , two-body breakup of D 3 + , and vibrational structure in O 2 + dissociation, will be presented.

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