The vibrational spectrum of indole: An inelastic neutron scattering study

We have obtained the first inelastic neutron scattering spectra of indole, a fundamental component of many important bio-molecular systems, including the amino acid tryptophan. Spectra of the powder, aligned crystals, and 1,3-dideuteroindole are given. This has provided the first clear comparison with ab initio frequency calculations of indole in the vapour and crystal phases. Details are extracted and assignment schemes given. The use of these indole assignments as a basis for understanding the spectra of substituted indoles is demonstrated by the assignment of the inelastic neutron scattering spectra of the 5- and 6-fluoroindoles.