The Revision Of Intermolecular Interactions In 1,3-Dinitrobenzene Crystal - The Role Of Nitro Groups In Optical Nonlinearity

Polarized Fourier transform-infrared (FT-IR) reflectance spectra and powder Raman spectra have been measured for 1,3-dinitrobenzene crystal in order to revise the assignments of bands by means of the oriented gas model reinforced with quantum chemical [density functional theory (OFT)] calculations. Longitudinal optical/transverse optical (LO-TO) splitting of some bands is observed indicating medium strong, long-range, dipole-dipole interactions. The analysis of overtones in the polarized FT-NIR spectra has allowed us to estimate the anharmonicity of vibrations in the crystal. The molecular motions of the nitro groups are analyzed on the basis of temperature-dependent polycrystalline IR spectra. Based on the values of the energy difference (Delta nu(el)) between the forbidden A(1g) -> B-2u transition in the benzene molecule in the gas phase and the first electronic transition in 1,3-dinitrobenzene, it has been concluded that the intermolecular interactions are medium strong. The nitro group interactions are proposed to play the main role in the optical nonlinearity. Copyright (C) 2010 John Wiley & Sons, Ltd.