More Information about the Spectra
During the time that it was operating (May 1985 - February 1998) TFXA recorded 4499 spectra from a huge variety of materials. This has continued with TOSCA - I (May 1998 - March 2000) and TOSCA - II (September 2000 - present) with over 14000 spectra recorded to date. These include biological materials, catalysts, fullerenes, superconductors, hydrogen-in-metal systems, polymers, organic, inorganic and organometallic compounds. Often as part of the work the spectrum of a reference material is required and the spectra on the database comprise some of these spectra. They have been selected on the basis of being well-characterised, pure compounds, recorded at low temperature (generally below 30 K). Because of the design of TFXA and TOSCA, the spectra are generally directly comparable with infrared and Raman spectra. For the future it is intended that as work on TOSCA is published, the INS spectra will be made available on this website.
The distinguishing features of INS spectra are:
There are no selection rules, all modes are allowed.
The scattering intensity depends on the inelastic neutron scattering cross-section, this is large for hydrogen and small for virtually everything else (including deuterium).
The intensity also depends on the amplitude of vibration, so motions that cause hydrogen to undergo large amplitude motions such as torsions and out-of-plane bending modes give stronger scattering. The combined effect of the cross-section and the dependence on the amplitude of vibration is that scattering by hydrogen (if present) dominates the spectrum.
The resolution of TOSCA is ~1.25% of the energy transfer, so the resolution is good below 2000 cm-1 and comparable to routine infrared and Raman spectra below 1000 cm-1.
Spectra of adsorbed species are not presently included as their interpretation requires additional information. However, in a particular case if there was a need for the spectra, please contact Stewart Parker at ISIS. Similarly, if a compound is not present on the database, it is always worth asking!
INS spectroscopy and its some of its applications are discussed in a paper in The Internet Journal
of Vibrational Spectroscopy.