Vibrational spectra and structure of crystalline 1–3 dinitrobenzene

Abstract

The analysis of Raman and infrared spectra of the H and D forms of rn dinitrobenzene in solution and in the crystalline state allows a tentative assignment of most of the observed bands. It gives no evidence for intermolecular dynamical coupling or for hydrogen bonding and favours Archer's structure. No angular dispersion is noticeable, but polaritons are observed.

The revision of intermolecular interactions in 1,3‐dinitrobenzene crystal—the role of nitro groups in optical nonlinearity

“…Out‐of‐plane deformation vibrations of CH groups are located below 1000 cm −1 . The band at 914–915 cm −1 (the most intense for ${\bf{\it{E}}}\vert \vert c$ ) was assigned as ν(1) by Bobrov et al 21 and is in agreement with Katon et al 's assignment 24. The bands at lower wavenumbers are in agreement with previous works as well as with the ones estimated on the basis of OGM.…”

“…The assignment of the bands is given in Table 1 along with the calculated wavenumbers and the values of PED. Letters B and K denote that a given assignment was the same as in works of Bobrov et al 21 and Katon et al 24 The polarized reflectance spectra are presented in Fig. 2.…”

“…In our polarized spectra, the highest wavenumber associated with these modes was at 1468 cm −1 (${\bf{\it{E}}}\vert \vert a$ ). This band was assigned as ν(19) (benzene ring vibration according to Wilson notation) by Bobrov et al 21 and as a combination of νCC + δCH by Katon et al 24 The band at 1438 cm −1 (${\bf{\it{E}}}\vert \vert b$ ) was not observed by Bobrov et al 21 but is in accordance with Katon et al 24 There is another band in this region—at 1419 cm −1 present in all three polarizations of comparable intensity—which did not appear in Bobrov et al 's spectra21 and was ascribed by Katon et al 24 to a combination mode of benzene ring. We decided to assign it to δCH as it was believed to couple with νCH(1) creating a combination mode in NIR (see Section on Anharmonicity).…”

“…The matter of intermolecular contacts has remained unclear also from the point of view of spectroscopy of the title crystal. There are several works devoted to spectroscopic investigations of this crystal,21–27 sometimes contradicting each other. The discrepancies mainly concern the assignment of nitro group vibrations as well as the strength of intermolecular interactions.…”

“…LO‐TO splitting is the frequency difference between these two modes. In the case of the title crystal, there were two papers dealing with the presence of polaritons 21, 22. Because organic materials can exhibit comparable or even better properties than their inorganic ‘precursors’, it is advisable to search for and/or study them.…”