Strong-field photoionization of vibrational ground-stateH2+andD2+molecules

We report on the observation of a high-energy “shoulder” in the kinetic-energy distribution of ${\mathrm{H}}^{+}$ and ${\mathrm{D}}^{+}$ ions formed in the interaction of ${\mathrm{H}}_2$ and ${\mathrm{D}}_2$ with ultrashort light pulses of an intensity higher than approximately ${10}^{15}\hspace{0.5em}{\mathrm{W}/\mathrm{c}\mathrm{m}}^2.$ It extends up to a kinetic energy of $\approx 8\hspace{0.5em}\mathrm{eV}.$ The “shoulder” ions are formed by Coulomb explosion after photoionization of the respective molecular ion. The shape of the “shoulder” indicates that photoionization of ${\mathrm{H}}_2^{+}$ in the vibrational ground state $v=0\mathrm{}$ and of ${\mathrm{D}}_2^{+}$ in $v=0,1\mathrm{}$ is the mechanism for atomic ion formation near the “shoulder” cutoff.