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Photoinduced reaction dynamics of nanocarbons

Date : Wednesday, February 21st, 2018 13:30 - 14:30 Place : Seminar Room 5 (A615), 6th Floor, ISSP Lecturer : Dr. Kaoru Yamazaki Affiliation : Institute for Materials Research, Tohoku University, Sendai, Japan Committee Chair : Taisuke OZAKI (63285)

Nanocarbons such as fullerene, carbon nanotube, and graphene are the fundamental materials for carbon-based nanotechnologies. Their optical and electronic properties heavily depend on their size and shape. In order to realize single-molecule scale structural engineering of nanocarbons using laser irradiation, we quantum-chemically investigated the mechanism of the photoinduced reaction dynamics of nanocarbons both in energy and time domains.

We first investigated the reaction paths of Stone–Wales rearrangement (SWR), i.e., π/2 rotation of two carbon atoms with respect to the midpoint of the bond, in graphene and carbon nanotube at the MS-CASPT2//SA-CASSCF level of multi-reference molecular orbital theory [1]. We found that the vibronic (electron-phonon) coupling play a crucial role to reduce the effective reaction barriers of the photoinduced defect formation of nanographene.

We next investigated that the fragmentation dynamics of the highly charged fullerene cation C60q+ (q = 20-60) produced by the irradiation of x-ray free electron laser pulse using on-the-fly classical trajectory calculations combined with density functional based tight-binding theory. We found that a two-step explosion mechanism governs the fragmentation dynamics [2]: C60q+ firstly ejects singly and multiply charged fast atomic cations Cz+ (z ≥ 1) to reduce its strong intramolecular Coulomb repulsion on a timescale of 10 fs. Thermal (statistical) evaporations of slow atomic and molecular fragments from the remaining core cluster subsequently occur on a timescale of 100 fs to 1 ps.

I will also briefly discuss our recent results on the real-time imaging of the near-/mid-IR induced coherent vibration of C60, which is considered as the initial step of the photoinduced fragmentation of C60 [3]

[1] K. Yamazaki et al., J. Phys. Chem. A 116, 11441 (2012).
[2] K. Yamazaki et al., J. Chem. Phys. 141, 121105 (2014).
[3] K. Yamazaki et al., to be submitted.

(Published on: Friday February 16th, 2018)