Raman Spectroscopy Studies On Non-coincidence Effect And Aggregation Structures Of The Molecular Containing Polar Bond

Intermolecular interactions are called weak interaction, is a very important force. It is always one of the very active research fields in chemical science. In this paper, non-coincidence effect and aggregation structures of the molecular containing polar bond have been studied by matrix isolation micro-Raman spectroscopy with the aid of density functional theory(DFT).Concentration effect, non-coincidence(NCE) effect and solvent effects of acetone have been investigated by the frequency shift of C=O stretching modes. Similarly, three other systems, ie,C=S stretching modes of ethylene trithiocarbonate(ET) and 1,3-Dithiole-2-thione(DT) and N=C=S stretching modes of methyl isothiocyanate, are also included in this thesis. This study shed new light on the understanding of the intermolecular interactions and solution organization style:(1) The micro-Raman spectrum in series of volume fractions of acetone in carbon tetrachloride solvent have been collected, as well as isotropic and anisotropic micro-Raman spectra. With the dilution of acetone in carbon tetrachloride solvent, the peak frequency of C=O stretching mode was observed to be blue-shift and the value of noncoincidence effect(NCE) was decreasing. The micro-Raman spectra of acetone isolated in an argon matrix in low-temperature were collected to further investigate those phenomena. It was found that the Raman mode ofυC=O is a single peak at 6 K, whereas it have been divided into two peaks after annealing at 16 K;the isotropic and anisotropic Raman spectra bands of υC=O completely overlapped at 6 K. At the same time, the B3LYP/6-311++G(d, p) were performed to calculate monomer, dimer of acetone and trimer of acetone. The calculation can well explain the experimental phenomena. The calculation shown that acetone molecules can form face to face, head-to-tail parallel dimeric form through strong intermolecular interaction. This dimeric structure may well explain NCE phenomenon.(2) The micro-Raman spectrum、isotropic and anisotropic micro-Raman spectra of ET and DT in different concentration have been collected respectivly. The NCE phenomenon of ET and DT firstly have been discoved as far as we known. For ET molecules,with the dilution of ET in chloroform solvent, the peak frequency of C=S stretching mode was observed to blue-shift,while the value of noncoincidence effect(NCE) was decline. In neat ET, the experimentallymeasured value of noncoincidence Δυnc is ～4.6 cm-1 for C=S stretching modes, which reduce to 1.30 cm-1, at the concentration of ET in mole fraction, χm(ET)=0.10. For DT molecules,these two phenomena are not obviously for C=S stretching modes. The absolute Raman cross section of C=S stretching was also measured and their behavior was unusual(first increasing and then decreasing with the decrease of concentration). At the same time, the B3LYP/6-311++G(d, p)were carried out geometry optimization for ET and DT monomer and dimer structure respectivly.It is discovered that they can form self-association completely different dimer structures by intermolecular interaction. The strong antiparallel head-to-tail vibrational coupling of the C=S oscillators in neighboring molecules accounts for the frequency shifts of the C=S stretching for ET molecules, while the DT molecules are no order. In short, the ET and DT dimeric structures may well explain their experimental phenomena respectively.(3) The micro-Raman spectra of methyl isothiocyanate isolated in an argon matrix in low-temperature were collected. It is found the Raman mode of υN=C=S is a single peak at 6k,however it have been split into two peaks after annealing at 25 K, which values are 656.6 cm-1and630.7 cm-1. With the annealing temperature increased from 25 K to 35 K, the intensity of υN=C=S tranform from 656.6 cm-1 to 630.7 cm-1 cm-1. The higher the annealing temperature, the more closer to the 298 K Raman spectra patterns. Finally, the B3LYP/6-311++G(d, p) were performed to calculate monomer, dimer of methyl isothiocyanate. The calculation results is accord with experimental phenomena. Methyl isothiocyanate molecules can form face to face, head-to-tail parallel dimer structure by intermolecular interactions.