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.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry