Raman Spectroscopy Studies On Non-coincidence Effect Of Several Different Types Of Molecules

Intermolecular weak interaction plays key important role in life science and catalysis fields and recently have been intensively investigated.Vibrational spectroscopy is a sensitive tool for investigation the solute structure and the solution environment changes.By monitoring the frequencies of the vibrational bands,structural changes can be observed.Non-coincidence(NCE)effect is a very important vibrational spectrum phenomenon that connected with intermolecular interactions.In this paper non-coincidence effects of several molecules have been studied by Raman spectroscopy with the aid of matrix isolation techonology and density functional theory.Concentration effect,non-coincidence(NCE)phenomenon and solvent effects of deuterated acetone,acetophenone and tetrahydrofuran have been investigated by the frequency shift of C=O stretching modes or C-H stretching modes respectively.In a word,this study shed new light on the understanding of the intermolecular interactions and solute aggregation structures changes in solution:(1)In this paper the NCE effect phenomenon and concentration effect of C-H stretching vibration modes of THF molecules have been intensively studied in the water and carbon tetrachloride solution respectively.The polarized and depolarized Raman spectra of C-H stretching modes of THF were recorded in water and carbon tetrachloride separately with the concentration ranging from 10% to 100%.The Raman frequencies of C-H stretching modes show a red shifting with the increase concentration of THF in water,and the value of non-coincidence effect(NCE)was increased accordingly.While the Raman frequencies of C-H stretching modes keeps constant with the increase concentration of THF in carbon tetrachloride and furthermore,the frequency of anisotropic and isotropic parts of C-H stretching vibration modes shows coincidence in all the range of concentration,no NCE phenomenon observed.In the meantime,the M?ller-Plesset(MP2)were performed to calculate monomer,dimer structure of THF to explain the above vibrational spectra behavior.The theoretical calculation showed in good agreement with our experimental data.In brief,the strong coupling of THF dimeric structure in water may well explain NCE phenomenon,while the weak coupling of THF in carbon tetrachloride shows no NCE phenomenon.(2)The Raman spectrum,isotropic and anisotropic Raman spectra of acetophenone in carbon tetrachloride with different concentration have been collected.With the dilution of acetophenone in carbon tetrachloride,the frequency of C=O stretching modes was observed to blue-shift,while the value of noncoincidence effect(NCE)was decline.At the same time,the B3LYP/6-311++G(d,p)were performed to calculate monomer,dimer of acetophenone.The theoretical calculations are in good agreement with the experimental data.(3)To have a clear cut idea about the non-coincidence effect of deuterated acetone,the Raman spectra of C=O stretching modes,as well as isotropic and anisotropic Raman spectra of deuterated acetone were recorded in carbon tetrachloride with solute concentration ranging from 30% to 100%.The Raman peak frequencies of C=O show a red shifting with the increase of solute concentrations in carbon tetrachloride.With the dilution of deuterium acetone in carbon tetrachloride,the value of non-coincidence effect(NCE)was decreasing.The micro-Raman spectra of deuterated acetone isolated in an argon matrix in low-temperature were collected.We found that the Raman mode of C=O is a single peak at 8K,but the single peak divided into two peaks after annealing at 25 K.At the same time,the M?ller-Plesset(MP2)were performed to calculate monomer,dimer of deuterium acetone.The calculation shows that deuterium acetone molecules may present head-to-tail parallel dimeric form through strong intermolecular interaction.The theoretical calculation are in good agreement with our experimental data.In short,the dimeric structure of deuterium acetone in carbon tetrachloride may well explain NCE phenomenon.