Raman Scattering Tensors for Single Crystals of Naphthalene

Abstract

The Raman scattering tensor for each gerade vibrational mode of crystalline naphthalene is evaluated from polarized Raman spectra of oriented single crystals. For molecular crystals, where the intermolecular interactions are weak, the form of the tensors is determined by the properties and symmetry of the molecule rather than the crystal; consequently, the symmetries of the gerade vibrations are readily identified. A comparison of these data with the phosphorescence and fluorescence spectra allows the fundamental vibrational frequencies to be assigned empirically. Except for one b2g mode and one b3g mode, the empirical assignments support those in the literature made on the basis of force field calculations. It is found that crystal effects on the gerade vibrations are small: frequency shifts are 2–4 cm−1, exciton splittings are less than 1 cm−1, and intensities are described qualitatively by the oriented gas model, although an unambiguous example of crystal-induced Fermi resonance is evident. Disagreement between the observed exciton splittings and some calculated splittings by N. Rich and D. Dows [Mol. Cryst. Liquid Cryst. 5, 111 (1968)] based on an atom–atom potential model may indicate that some finer features of the intermolecular potential are not well represented by such a model. The temperature dependence of the Raman linewidth and line shape is documented.

Method of Heavily Doped Isotopic Mixed Crystal for Determination of Exciton Splittings and Normal Modes: Raman Spectra of Naphthalene

“…Stenman 3 agrees with the interpretation of Hanson and Gee. 2 In addition he sees a doublet near 466 (465 and 470 em-I). He assigns the new mode seen at 470 cm-I as a combination of the 392 cml fundamental and a lattice vibration.…”

“…In: the neat crystal of naphthalene-hg we see doublets at frequencies 933.5, 937.5 and 947, 951 cm-I • In the 50% naphthalene-hg mixed crystal the doublet features of both these bands are replaced by broad bands with peaks at 935 and 949.5 cml • It is interesting to compare our results with those obtained by Hanson and Gee. 2 In the region of 390 cm-I they see two modes, of frequencies 388 and 392 cm-l at room temperature, and assign them as b 2g and bIg fundamentals, respectively. They see only one mode near 466 cm-1 at room temperature and assign this as a b2g mode.…”

Resonance Raman Spectroelectrochemistry of Tetracyanoquinodimethane Dianion and Tetrathiofulvalene Monocation

“…Although both nontotally symmetric and totally symmetric modes can be observed in NR spectroscopy, it is a general rule that the totally symmetric vibrations are more intense (26). Although both nontotally symmetric and totally symmetric modes can be observed in NR spectroscopy, it is a general rule that the totally symmetric vibrations are more intense (26).…”

“…Searching the cyanocarbon literature for oxygen containing compounds related to TCNQ, it was discovered that a carbanion [~, a-dicyano-p-toluoyl cyanide (DCTC-)] has an absorption maximum at 480 nm (26). The sodium salt of this carbanion can be prepared by the reaction of TCNQ neutral and NaNO2 (25).…”

Resolution Enhancement of Raman Spectra of Solids Using True Linear Prediction and Deconvolution

“…3±6 However, the exciton structure of the crystal levels is still largely unexplained. With respect to earlier investigations, those of Hanson and Gee 7 and Stenman 8 report observed exciton splittings, although their observations were mostly based on directly observed ® ne structure. Prasad and Kopelman used mixed isotopic crystals of protonated and deuterated naphthalene to study line separations as a function of mixing ratio and in that way detected several cases of splittings interpretable as true exciton splittings.…”