Librational Amplitudes: Raman and Nuclear Quadrupole Resonance Spectra of p-Dichlorobenzene and p-Dichlorobenzene-d4

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Abstract
Mean‐squared angular amplitudes of vibration are calculated for a one‐dimensional crystal model with torsional nearest‐neighbor interaction. Vibrational modes with nonzero wave vector are all included in the averaging, and the effect is shown to be amplification of amplitude of magnitude dependent on the extent of interaction. Raman spectra for the 0–100‐cm−1 region of crystalline p‐dichlorobenzene and p‐dichlorobenzene‐d4 are reported and an assignment suggested for these librational fundamentals. Raman frequencies so assigned are used in an approximate calculation of the temperature dependence of nuclear quadrupole resonance frequencies of p‐dichlorobenzene and the results compared with experiment. An interpretation is given of the result of Dinesh and Narasimhan for the nuclear quadrupole resonance frequency of HgCl2.