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

We theoretically investigated the stability of highly charged C60 z+ cations produced from C60 with an ultrashort intense laser pulse of λ∼1800 nm. We first calculated the equilibrium structures and vibrational frequencies of C60 z+ as well as C60. We then calculated key energies relevant to dissociation of C60 z+, such as the excess vibrational energy acquired upon sudden tunnel ionization from C60. By comparing the magnitudes of the calculated energies, we found that C60 z+ cations up to z∼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 [Phys. Rev. Lett. 93, 043001 (2004)] that almost only intact parent C60 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 C60 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 C60 and C60 z+ by an intense near-infrared pulse. The results indicate that large-amplitude vibration with energy of >10 eV is induced in the delocalized hg (1) -like mode of C60 z+.