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Assignment of the Internal Vibrational Modes of C70 by Inelastic Neutron Scattering Spectroscopy and Periodic-DFT.

Refson K, Parker SF - ChemistryOpen (2015)

Bottom Line: Unfortunately, many of the modes are either forbidden or have very low infrared or Raman intensity, even if allowed.We have obtained a new INS spectrum from a large sample recorded at the highest resolution available.We demonstrate that all previous assignments are incorrect in at least some respects and propose a new assignment based on periodic density functional theory (DFT) that successfully reproduces the INS, infrared, and Raman spectra.

View Article: PubMed Central - PubMed

Affiliation: ISIS Facility, Science and Technology Facilities Council (STFC), Rutherford Appleton Laboratory Chilton, Didcot, OX11 0QX, UK ; Department of Physics, Royal Holloway, University of London Egham, TW20 0EX, UK.

ABSTRACT
The fullerene C70 may be considered as the shortest possible nanotube capped by a hemisphere of C60 at each end. Vibrational spectroscopy is a key tool in characterising fullerenes, and C70 has been studied several times and spectral assignments proposed. Unfortunately, many of the modes are either forbidden or have very low infrared or Raman intensity, even if allowed. Inelastic neutron scattering (INS) spectroscopy is not subject to selection rules, and all the modes are allowed. We have obtained a new INS spectrum from a large sample recorded at the highest resolution available. An advantage of INS spectroscopy is that it is straightforward to calculate the spectral intensity from a model. We demonstrate that all previous assignments are incorrect in at least some respects and propose a new assignment based on periodic density functional theory (DFT) that successfully reproduces the INS, infrared, and Raman spectra.

No MeSH data available.


Comparison of the a) TOSCA INS spectrum of C70 at 7 K with spectra simulated using literature assignments: b) for the gas phase by GAUSSIAN 98 (D5h symmetry)19 and c) by an ab initio molecular dynamics simulation.26
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fig04: Comparison of the a) TOSCA INS spectrum of C70 at 7 K with spectra simulated using literature assignments: b) for the gas phase by GAUSSIAN 98 (D5h symmetry)19 and c) by an ab initio molecular dynamics simulation.26

Mentions: The need for a new assignment is demonstrated in Figure 4, which compares our new INS spectrum (Figure 4 a) with the INS spectra predicted by literature results assuming an isolated (gas phase) molecule19 (Figure 4 b) and by an ab initio molecular dynamics simulation26 (Figure 4 c). It can be seen that while the overall profile is approximately correct, both simulated spectra are wrong in detail, particularly in the 450–800 cm−1 region. For the present work, we have chosen to model the system with ab initio lattice dynamics (as implemented in the DFT code, CASTEP), that was successfully used for C60.27


Assignment of the Internal Vibrational Modes of C70 by Inelastic Neutron Scattering Spectroscopy and Periodic-DFT.

Refson K, Parker SF - ChemistryOpen (2015)

Comparison of the a) TOSCA INS spectrum of C70 at 7 K with spectra simulated using literature assignments: b) for the gas phase by GAUSSIAN 98 (D5h symmetry)19 and c) by an ab initio molecular dynamics simulation.26
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4608530&req=5

fig04: Comparison of the a) TOSCA INS spectrum of C70 at 7 K with spectra simulated using literature assignments: b) for the gas phase by GAUSSIAN 98 (D5h symmetry)19 and c) by an ab initio molecular dynamics simulation.26
Mentions: The need for a new assignment is demonstrated in Figure 4, which compares our new INS spectrum (Figure 4 a) with the INS spectra predicted by literature results assuming an isolated (gas phase) molecule19 (Figure 4 b) and by an ab initio molecular dynamics simulation26 (Figure 4 c). It can be seen that while the overall profile is approximately correct, both simulated spectra are wrong in detail, particularly in the 450–800 cm−1 region. For the present work, we have chosen to model the system with ab initio lattice dynamics (as implemented in the DFT code, CASTEP), that was successfully used for C60.27

Bottom Line: Unfortunately, many of the modes are either forbidden or have very low infrared or Raman intensity, even if allowed.We have obtained a new INS spectrum from a large sample recorded at the highest resolution available.We demonstrate that all previous assignments are incorrect in at least some respects and propose a new assignment based on periodic density functional theory (DFT) that successfully reproduces the INS, infrared, and Raman spectra.

View Article: PubMed Central - PubMed

Affiliation: ISIS Facility, Science and Technology Facilities Council (STFC), Rutherford Appleton Laboratory Chilton, Didcot, OX11 0QX, UK ; Department of Physics, Royal Holloway, University of London Egham, TW20 0EX, UK.

ABSTRACT
The fullerene C70 may be considered as the shortest possible nanotube capped by a hemisphere of C60 at each end. Vibrational spectroscopy is a key tool in characterising fullerenes, and C70 has been studied several times and spectral assignments proposed. Unfortunately, many of the modes are either forbidden or have very low infrared or Raman intensity, even if allowed. Inelastic neutron scattering (INS) spectroscopy is not subject to selection rules, and all the modes are allowed. We have obtained a new INS spectrum from a large sample recorded at the highest resolution available. An advantage of INS spectroscopy is that it is straightforward to calculate the spectral intensity from a model. We demonstrate that all previous assignments are incorrect in at least some respects and propose a new assignment based on periodic density functional theory (DFT) that successfully reproduces the INS, infrared, and Raman spectra.

No MeSH data available.