Ionization and fragmentation of endohedral fullerenes Ho$_{3}$N@C$_{80}$ in an intense femtosecond laser field*

Gas phase endohedral fullerenes Ho$_{3}$N@C$_{80}$ have been studied by excitation with intense femtosecond laser pulses at 800nm. Multiple charge states were found after the laser excitation. The highest charge state of the mother molecules was found to be Ho$_{3}$N@C$_{80}^{4+}$. The molecules absorb multiple photons during the excitation, and may release extra energy by evaporating multiple C$_{2}$ dimers from the carbon cage. Ho$_{3}$N@C$_{70}^{\mathrm{n+}}$ and Ho$_{3}$N@C$_{50}^{\mathrm{n+}}$ were found to be more stable than other fullerene productions. The molecules may also fragment into Ho$^{+}$, HoC$_{2}^{+}$ and HoCN$^{+}$ fragments. The yields of different fragments dependence on laser intensity will be compared to understand the fragmentation pathways.