Neutron Spectroscopy of Naphthalene Crystal Internal Phonon Modes

Abstract Spectra of the incoherent inelastic neutron scattering from naphthalene crystals in the region of internal phonon modes (170 to 1300 cm −1 ) are studied at the temperatures 296, 80, and 4.7 K. The spectra obtained are quantitatively processed by means of a direct spectral procedure. The ambiguity present before in the frequency spectrum of the internal phonon modes of the crystal in the region from 170 to 1300 cm −1 is eliminated basing on these experimental results together with results on Kaman‐Mandelstam scattering spectra and infrared absorption. The a u mode frequencies inactive in optical spectra are determined. The possibility is indicated to use the displacement amplitude of the free molekule hydrogen atoms in order to describe the investigated phonon modes in the crystal.

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