Molecular interactions with photons

Determining Structure by Molecular Interactions with Photons ... 

Organic molecules have useful optical and electronic functions that can be easily controlled by the structure, substituent, or external fields. Molecular interactions and organized molecular assemblies also can afford much higher functions than isolated or randomly distributed molecules. Photons have many superior properties such as wavelength, polarization, phase, ultrashort pulse, or parallel processability. Through interactions of molecules or molecular assemblies with photons, many properties of photons can be directly converted to changes in physical properties of materials such as fluorescence, absorption,... 

Given the ability of nanochemistry to provide functional materials of practical utility in the near future, the elaborative quantum-chemical calculations of clusters are of significant value because interesting individual molecules or small clusters can be developed as viable functional materials and devices. The prediction of properties of nanomaterials, from a nanoscopic determination of the properties of individual atoms, molecules, or clusters, is based on molecular interactions (with ion/atom/molecule/ electron/photon) and the resulting molecular structures (clustering/aggregation by self-assembly and self-synthesis process). In this context, we have carried out detailed... 

The interactions of photons with molecules are described by molecular cross-sections. For IR spectroscopy the cross-section is some two orders of magnitude smaller with respect to UV or fluorescence spectroscopy but about 10 orders of magnitude bigger than for Raman scattering. The peaks in IR spectra represent the excitation of vibrational modes of the molecules in the sample and thus are associated with the various chemical bonds and functional groups present in the molecules. The frequencies of the characteristic absorption bands lie within a relatively narrow range, almost independent of the composition of the rest of the molecule. The relative constancy of these group frequencies allows determination of the characteristic... 

As molecular dipoles vibrate, they emit photons which excite vibrations in nearby molecules. In turn, these molecules emit photons which interact with the initiating molecule. In this way, the molecules interact by exchanging photons. Again there are two modes. In one case, the vibrations of the molecules occur in phase with one another. In the second case, they interact out of phase. The energy of the system is lower when the vibrations are in phase, so this case creates attractions between the molecules, while the out-of-phase case creates repulsions. Since the energy of the in phase case is lower, the net effect is attraction. 

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