Inelastic Scattering of Thermal Neutrons by Some Benzene Derivatives

Thermal neutron scattering in phenol, hydroquinone and pyrogallol in the liquid state was investigated. The E0 energy of incident neutrons was varied between 15 and 50 m e V and the scattering angles between 5° and 108°. The quasi-elastic maximum width of scattered neutron spectra were determined for (0 .1 Å-2 < K2 < 9 Å-2). The obtained and computed values were compared by the LarssoniBergstedt method. Very good agreement wasobtained between theexperimental and theoretical data for τ0 = 10-12 sec; ℓ = 0.76 Å. Theresult obtained can be explained by the contribution at the quasi-elastic maximum of neutron interactions with rotational oscillatory motion around an axis contained within a molecular plane. This interpretation can be justified by comparing our results with those obtained in the i.r. spectrum of benzene. The transition corresponding to a wave number of approximately 60 cm-1 was observed in the quasi-elastic scattered neutron spectra of all substances studied and it was ascribed to molecular rotational oscillation around an axis contained within the molecule plane. The observed maxima in the three spectra corresponding to the wave numbers, 434 cm-1 (phenol), 412 cm-1 (hydroquinone) and 463 cm-1 (pyrogallol), are ascribed to superposing of the OH group vibration motions and benzenic ring deformation. A third maximum can be observed for hydroquinone and pyrogallol, corresponding to a wave number 150 cm-1, characteristic for the hydrogen bond. (author)