Intramolecular vibronic dynamics in molecular solids: ${\mathrm{C}}_{60}$

Intramolecular vibronic dynamics in molecular solids: $C_{60}$

L. Kjeldgaard, T. Käämbre, J. Schiessling, I. Marenne, J. N. O’Shea, J. Schnadt, C. J. Glover, M. Nagasono, D. Nordlund, M. G. Garnier, L. Qian, J.-E. Rubensson, P. Rudolf, N. Mårtensson, J. Nordgren, and P. A. Brühwiler

Phys. Rev. B 72, 205414 – Published 9 November 2005

Abstract

Vibronic coupling in solid $C_{60}$ has been investigated with a combination of resonant photoemission spectroscopy (RPES) and resonant inelastic x-ray scattering (RIXS). Excitation as a function of energy within the lowest unoccupied molecular orbital resonance yielded strong oscillations in intensity and dispersion in RPES, and a strong inelastic component in RIXS. Reconciling these two observations establishes that vibronic coupling in this core hole excitation leads to predominantly inelastic scattering and localization of the excited vibrations on the molecule on a femtosecond time scale. The coupling extends throughout the widths of the frontier valence bands.

Received 9 June 2005

DOI:https://doi.org/10.1103/PhysRevB.72.205414

Authors & Affiliations

L. Kjeldgaard^1,*, T. Käämbre^1,†, J. Schiessling^1,‡, I. Marenne², J. N. O’Shea^1,§, J. Schnadt^1,∥, C. J. Glover^3,¶, M. Nagasono^3,**, D. Nordlund³, M. G. Garnier^3,††, L. Qian¹, J.-E. Rubensson¹, P. Rudolf^4,2, N. Mårtensson^1,3, J. Nordgren¹, and P. A. Brühwiler^1,5,‡‡

¹Department of Physics, Uppsala University, Box 530, SE-751 21 Uppsala, Sweden
²LISE, Facultès Universitaires Notre Dame de la Paix, Rue de Bruxelles 61, B-5000 Namur, Belgium
³MAX-lab, University of Lund, Box 118, SE-221 00 Lund, Sweden
⁴Materials Science Centre, University of Groningen, Nijenborgh 4, NL-9747 AG Groningen, The Netherlands
⁵Empa, Materials Science and Technology, Lerchenfeldstrasse 5, CH-9014 St. Gallen, Switzerland

^*Present address: MAX-lab, University of Lund, Box 118, SE-221 00 Lund, Sweden.
^†Present address: Institute of Physics, Tartu University, Riia 142, EE-51014 Tartu, Estonia.
^‡Corresponding author. Email address: joachim.schiessling@fysik.uu.se; Present address: MAX-lab, University of Lund, Box 118, SE-221 00 Lund, Sweden.
^§Present address: School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD, United Kingdom.
^∥Present address: Department of Physics and Astronomy, University of Aarhus, Ny Munkegade, 8000 Aarhus C, Denmark.
^¶Present address: Department of Electronic Materials Engineering, Research School of Physical Sciences and Engineering, Australian National University Canberra, Australia.
^**Present address: Universität Hamburg, Luruper Chausee 149, 22761 Hamburg, Germany.
^††Present address: Institut de Physique, Université de Neuchâtel rue Breguet 1, 2000 Neuchâtel, Switzerland.
^‡‡Corresponding author. Email address: paul.bruehwiler@empa.ch

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Vol. 72, Iss. 20 — 15 November 2005

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Figure 1
(Color online) (a) A schematic of the spectroscopies employed, showing the relationships between the intermediate and final electronic states. Photoemission (PES) and resonant photoemission (RPES) have the same final state, whereas resonant inelastic soft-x-ray emission (RIXS) leaves the molecule in its ground state. (b) (left) A simplified Franck-Condon diagram shows vibrational potentials for the ground, valence-hole $5 h_{u}^{- 1}$ , and $1 s$ excited $1 s^{- 1} 3 t_{u}^{+ 1}$ states. The transitions depicted in (a) are indicated by solid arrows in the corresponding colors; dashed arrows suggest the role of energy dissipation in the intermediate state. (b) (right) The LUMO-derived resonance is located in the fundamental gap formed by the solid-state HOMO- and LUMO-derived-bands (Ref. 20). The simulation in terms of vibrational excitation, cf. Fig. 2, suggests a plausible distribution of the observed spectral linewidth.Reuse & Permissions
Figure 2
(Color online) (a) RPES and direct PES data for solid $C_{60}$ , taken at the indicated photon energies. For each RPES spectrum the direct PES contribution shown has been subtracted from raw RPES data. The molecular levels are labeled; uppercase indices indicate the valence-hole final state. (b) Simulation and XAS data taken at the LUMO-derived resonance. The (0,0) line of the simulation is rescaled by 0.12 for better comparison. The variation of the RPES signal is plotted by symbols on the curve. The value of each symbol corresponds to the peak areas of the respective valence band spectrum shown in (a). See the text for more details.Reuse & Permissions
Figure 3
(Color online) (a) The spectra from Fig. 2 normalized to the area of the HOMO-2 structure as explained in the text, plotted on a kinetic energy scale. Two line shapes of the HOMO from direct photoemission, rescaled to match the extremal intensities of RPES and separated by 0.19 eV, are shown for comparison of line shape and energy separation for the two extreme cases in RPES. (b) Evolution of the peak areas of the three valence structures while exciting across the LUMO-derived resonance. Direct PES (RPES) is shown as open (filled) circles. Within the interval 284 to 285 eV, the contribution from direct photoemission has been subtracted from the raw RPES signal.Reuse & Permissions
Figure 4
(Color online) RIXS data (dotted lines) taken at photon energies similar to the RPES data. The position of the elastic peak is indicated by a Gaussian (solid lines) centered at the incident photon energy. In the lowest three spectra the intensity of the elastic peak is estimated by the constraint that the result of subtracting the elastic peak should not induce structures not already apparent in the raw data.Reuse & Permissions

Physical Review B

covering condensed matter and materials physics

Intramolecular vibronic dynamics in molecular solids: $C_{60}$

L. Kjeldgaard, T. Käämbre, J. Schiessling, I. Marenne, J. N. O’Shea, J. Schnadt, C. J. Glover, M. Nagasono, D. Nordlund, M. G. Garnier, L. Qian, J.-E. Rubensson, P. Rudolf, N. Mårtensson, J. Nordgren, and P. A. Brühwiler

Phys. Rev. B 72, 205414 – Published 9 November 2005

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Physical Review B

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Intramolecular vibronic dynamics in molecular solids: C60

L. Kjeldgaard, T. Käämbre, J. Schiessling, I. Marenne, J. N. O’Shea, J. Schnadt, C. J. Glover, M. Nagasono, D. Nordlund, M. G. Garnier, L. Qian, J.-E. Rubensson, P. Rudolf, N. Mårtensson, J. Nordgren, and P. A. Brühwiler

Phys. Rev. B 72, 205414 – Published 9 November 2005

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Intramolecular vibronic dynamics in molecular solids: $C_{60}$