Mass-analyzed velocity map imaging of doubly charged photofragments from C70

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(vib)/2 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 τ. The energy of a Raman active mode is maximized if τ is chosen to equal an integer multiple of T(vib) and it is minimized if τ 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 pentagon/pentagon defects produced by a preceding SWR, which confirms the earliest mechanistic speculations of Smalley et al. [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.

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Mass-Resolved Velocity Map Imaging of Doubly Charged Photofragments from C60

Katayanagi¹,

Mitsuke²

2015

Bulletin of the Chemical Society of Japan

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Mass-resolved velocity map images have been measured for C60−2n2+ and C60−2n3+ (n ≥ 1) produced by photoionization of C60 with synchrotron radiation. A four-element electrostatic compound lens system was substituted for a conventional three-element system. This produced excellent time resolution, i.e., good mass-to-charge resolution, and negligible overlap between neighboring cluster ions. The translational temperatures for the C60−2n2+ ions were estimated from their velocity map images by assuming the Maxwell–Boltzmann distributions. Moreover, the improved resolution allowed observing a two-dimensional (2D) projection of three-dimensional velocity distribution of each fragment. The 2D projection of C582+ results from convolution of a narrow velocity distribution of the C60 molecular beam and a nascent isotropic profile of photodissociated C582+.

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Mass-analyzed velocity map imaging of doubly charged photofragments from C70

Cited by 4 publications

References 36 publications

Simulation of Nuclear Dynamics of C60: From Vibrational Excitation by Near-IR Femtosecond Laser Pulses to Subsequent Nanosecond Rearrangement and Fragmentation

Simulation of Nuclear Dynamics of C60: From Vibrational Excitation by Near-IR Femtosecond Laser Pulses to Subsequent Nanosecond Rearrangement and Fragmentation

Nanosecond simulations of the dynamics of C60 excited by intense near-infrared laser pulses: Impulsive Raman excitation, rearrangement, and fragmentation

Mass-Resolved Velocity Map Imaging of Doubly Charged Photofragments from C60

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