Clear evidence of zero-photon dissociation of H$_{2}^{+}$ in intense few cycle laser pulses*

Evidence of net zero-photon dissociation is elusive, since the low kinetic energy release, which is the signature of this process, can also be due to resonance enhanced multi-photon ionization (REMPI) of H$_{2}$ [Posthumus \textit{et al}., Phys. Rev. Lett. \textbf{101}, 233004 (2008)]. To eliminate the competing REMPI process we have studied an H$_{2}^{+}$ beam target. Explicitly, we measured very low kinetic energy release (down to 0 eV) upon dissociation of H$_{2}^{+}$ using a coincidence three dimensional momentum imaging technique. Our experimental findings are supported by the solutions of the time-dependent Schr\"{o}dinger equation for the conditions used in the experiment. Our results suggest that the zero-photon dissociation mechanism, most visible at $\sim $10$^{13}$ W/cm$^{2}$, is enhanced for short laser pulses ($\le $10 fs).