Nanosecond simulations of the dynamics of C ₆₀ excited by intense near-infrared laser pulses: Impulsive Raman excitation, rearrangement, and fragmentation

Impulsive Raman excitation of C ₆₀ by single or double pulses of near-infrared wavelength λ 1800 nm was investigated by using a time-dependent adiabatic state approach combined with the density functional theory method. We confirmed that the vibrational energy stored in a Raman active mode of C ₆₀ is maximized when T _p ∼ T _vib2 in the case of a single pulse, where T _p is the pulse length and T _vib is the vibrational period of the mode. In the case of a double pulse, mode selective excitation can be achieved by adjusting the pulse interval . The energy of a Raman active mode is maximized if is chosen to equal an integer multiple of T _vib and it is minimized if is equal to a half-integer multiple of T _vib. We also investigated the subsequent picosecond or nanosecond dynamics of Stone-Wales rearrangement (SWR) and fragmentation by using the density-functional based tight-binding semiempirical method. We present how SWRs are caused by the flow of vibrational kinetic energy on the carbon bond network of C ₆₀. In the case where the h _g(1) prolate-oblate mode is initially excited, the number of SWRs before fragmentation is larger than in the case of a _g(1) mode excitation for the same excess vibrational energy. Fragmentation by C ₂ ejection C ₆₀ → C ₅₈ C ₂ is found to occur from strained, fused pentagonpentagon defects produced by a preceding SWR, which confirms the earliest mechanistic speculations of Smalley J. Chem. Phys. 88, 220 (1988). The fragmentation rate of C ₂ ejection in the case of h _g(1) mode excitation does not follow a statistical description as employed for instance in the Rice-Ramsperger-Kassel (RRK) theory, whereas the rate for a _g(1) mode excitation does follow the prediction by RRK. We also found for the h _g(1) mode excitation that the nonstatistical nature affects the distribution of barycentric velocities of fragments C ₅₈ and C ₂. This result suggests that it is possible to control rearrangement and subsequent bond breaking in a nonstatistical way by initial selective mode excitation.