ISIS Neutron and Muon Source Data Journal

Rotational recoil of methyl groups in the inelastic neutronic scattering spectra: a constant-Q quantitative study

Abstract: Methyl (-CH3) rotational tunnelling is a well-known phenomenon and is being accurately investigated by quasi-elastic neutron scattering for decades. In a recent paper, we investigated the vibrational dynamics of -phase crystalline methanol and its three isotopic substitutes by inelastic neutron scattering (INS) on TOSCA, classical molecular dynamics, and ab initio DFT lattice dynamics. A good quantitative match between INS and simulated spectra was possible only with the inclusion of a large heuristic background to the simulated data. After a careful study of the problem, it turned out that such a background was present both in conjunction with -CH3 and -CD3, although in the former case it was in percentage more intense than in the latter. In addition, this extra-signal appeared to be completely unrelated to either multiple scattering contaminations or multiphonon contributions, and for these reasons it was interpreted as an exclusive effect of the methyl rotational recoil. However, some doubts still remain, since INS experimental data on formic acid, which does not contains methyl groups, also show the existence of some background. We propose, then, to collect INS spectra of CH3OH and HCOOH in three different scattering conditions each, in order to have an experimental control over the multiple scattering contaminations, and we expect to provide some direct insight to the nature of this background.

Principal Investigator: Dr Simone De Panfilis
Experimenter: Dr Ferdinando Formisano
Experimenter: Dr Daniele Colognesi
Local Contact: Dr Duc Le
Experimenter: Dr Miguel Angel Gonzalez

DOI: 10.5286/ISIS.E.RB2610016

ISIS Experiment Number: RB2610016

Publisher: STFC ISIS Neutron and Muon Source

Data format: RAW/Nexus
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Data Citation

The recommended format for citing this dataset in a research publication is as:
[author], [date], [title], [publisher], [doi]

For Example:
Dr Simone De Panfilis et al; (2026): Rotational recoil of methyl groups in the inelastic neutronic scattering spectra: a constant-Q quantitative study, STFC ISIS Neutron and Muon Source, https://doi.org/10.5286/ISIS.E.RB2610016

Data is released under the CC-BY-4.0 license.