Slow protons as a signature of zero-photon dissociation of H2+ in intense laser fields

We have observed protons with near-zero kinetic energy that originate from the interaction of a frequency tripled (λ = 266 nm), 250 fs intense Ti:sapphire laser with H2 molecules. These protons are tentatively ascribed to zero-photon dissociation (ZPD) of H2+. Earlier quantum mechanical calculations show that such a process should occur due to the partial escape of the vibrational wavepacket that is trapped in the laser-induced, adiabatic well above the one-photon crossing of dressed Floquet states. The fact that slow protons are also observed at the second harmonic (λ = 400 nm), but to a lesser extent, is consistent with the ZPD explanation.