Theoretical investigation of the stability of highly charged C60 molecules produced with intense near-infrared laser pulses

Abstract

We theoretically investigated the stability of highly charged ${\mathrm{C}}_{60}^{z+}$ cations produced from ${\mathrm{C}}_{60}$ with an ultrashort intense laser pulse of $\lambda \sim 1800\mathrm{nm}$ . We first calculated the equilibrium structures and vibrational frequencies of ${\mathrm{C}}_{60}^{z+}$ as well as ${\mathrm{C}}_{60}$ . We then calculated key energies relevant to dissociation of ${\mathrm{C}}_{60}^{z+}$ , such as the excess vibrational energy acquired upon sudden tunnel ionization from ${\mathrm{C}}_{60}$ . By comparing the magnitudes of the calculated energies, we found that ${\mathrm{C}}_{60}^{z+}$ cations up to $z\sim 12$ can be produced as a stable or quasistable (microsecond-order lifetime) intact parent cation, in agreement with the recent experimental report by V. R. Bhardwaj et al. [Phys. Rev. Lett. 93, 043001 (2004)] that almost only intact parent ${\mathrm{C}}_{60}^{z+}$ cations up to $z=12$ are detected by a mass spectrometer. The results of Rice-Ramsperger-Kassel-Marcus calculation suggest that the lifetime of ${\mathrm{C}}_{60}^{z+}$ drastically decreases by ten orders of magnitude as $z$ increases from $z=11$ to $z=13$ . Using the time-dependent adiabatic state approach, we also investigated the vibrational excitation of ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{60}^{z+}$ by an intense near-infrared pulse. The results indicate that large-amplitude vibration with energy of $>10\mathrm{eV}$ is induced in the delocalized $h_g\left(1\right)$ -like mode of ${\mathrm{C}}_{60}^{z+}$ .