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Magnetic Raman optical activity of gases provides unique information about their electric and magnetic properties.M agnetic Raman optical activity has recently been observed in ap aramagnetic gas (Angew.C hem. Int. Ed. 2012,5 1, 11058;A ngew.C hem. 2012,1 24, 11220). In diamagnetic molecules,i th as been considered too weak to be measurable.However,inchlorine,bromine and iodine vapors, we could detect asignificant signal as well. Zeeman splitting of electronic ground-state energy levels cannot rationalizet he observed circular intensity difference (CID) values of about 10 À4 .T hese are explicable by participation of paramagnetic excited electronic states.T hen as imple model including one electronic excited state provides reasonable spectral intensities. The results suggest that this kind of scattering by diamagnetic molecules is ag eneral event observable under resonance conditions.T he phenomenon sheds new light on the role of excited states in the Raman scattering, and mayb eu sed to probe molecular geometry and electronic structure.Different interaction of molecules with left and right circularly polarized light (CPL) in the presence of magnetic field can be explored in optical devices and provides unique information about geometry and electronic structure of molecules.T he Faraday effect, for example,i sw idely used in analytical chemistry,optical instrumentation, and laser and communication appliances. [1] Likewise,t he magnetic circular dichroism spectroscopy matured into au seful tool to probe geometry and electronic states in aw ide range of systems including new fullerene materials. [2] CPL components in the interstellar space,p ossibly caused by supernova magnetic fields, [3] have even been suggested to be responsible for the chirality encountered in living organisms. [4] Recently,w er eported observation of another phenomenon, paramagnetic Raman optical activity (ROA) of gasphase NO 2 . [5] TheR OA spectrometer measures at iny intensity difference in scattering of the right and left CPL (I R ÀI L ). Forthe nitrogen dioxide the observation was possible due to the presence of afree electron lending it its magnetic moment of the order of the Bohr magneton (ca. 9.27 10 À24 JT À1 ). In addition, anear resonance of the incident laser light with NO 2 electronic states increased the Raman cross-section and made the observation easier.T he effect was explained on the basis of ground-state rotational energy levels split in the external magnetic field, which also provided selection rules for the observed transitions.F or example,a bsorption of left or right CPL can occur only when the magnetic quantum number changes by aunity. [6] Such ground-state splitting would not allow for as imilar detectable event in the diamagnetic gases,where the magnetic moment is close to the nuclear magneton (5.05 10 À27 JT À1 ), that is,1 840 times smaller than in the paramagnetic case.T o our great surprise,however, the Cl 2 ,Br 2 and I 2 halogen gases or vapors,when kept in the magnetic field, exhibited astrong ROAs ignal as w...
Magnetic Raman optical activity of gases provides unique information about their electric and magnetic properties.M agnetic Raman optical activity has recently been observed in ap aramagnetic gas (Angew.C hem. Int. Ed. 2012,5 1, 11058;A ngew.C hem. 2012,1 24, 11220). In diamagnetic molecules,i th as been considered too weak to be measurable.However,inchlorine,bromine and iodine vapors, we could detect asignificant signal as well. Zeeman splitting of electronic ground-state energy levels cannot rationalizet he observed circular intensity difference (CID) values of about 10 À4 .T hese are explicable by participation of paramagnetic excited electronic states.T hen as imple model including one electronic excited state provides reasonable spectral intensities. The results suggest that this kind of scattering by diamagnetic molecules is ag eneral event observable under resonance conditions.T he phenomenon sheds new light on the role of excited states in the Raman scattering, and mayb eu sed to probe molecular geometry and electronic structure.Different interaction of molecules with left and right circularly polarized light (CPL) in the presence of magnetic field can be explored in optical devices and provides unique information about geometry and electronic structure of molecules.T he Faraday effect, for example,i sw idely used in analytical chemistry,optical instrumentation, and laser and communication appliances. [1] Likewise,t he magnetic circular dichroism spectroscopy matured into au seful tool to probe geometry and electronic states in aw ide range of systems including new fullerene materials. [2] CPL components in the interstellar space,p ossibly caused by supernova magnetic fields, [3] have even been suggested to be responsible for the chirality encountered in living organisms. [4] Recently,w er eported observation of another phenomenon, paramagnetic Raman optical activity (ROA) of gasphase NO 2 . [5] TheR OA spectrometer measures at iny intensity difference in scattering of the right and left CPL (I R ÀI L ). Forthe nitrogen dioxide the observation was possible due to the presence of afree electron lending it its magnetic moment of the order of the Bohr magneton (ca. 9.27 10 À24 JT À1 ). In addition, anear resonance of the incident laser light with NO 2 electronic states increased the Raman cross-section and made the observation easier.T he effect was explained on the basis of ground-state rotational energy levels split in the external magnetic field, which also provided selection rules for the observed transitions.F or example,a bsorption of left or right CPL can occur only when the magnetic quantum number changes by aunity. [6] Such ground-state splitting would not allow for as imilar detectable event in the diamagnetic gases,where the magnetic moment is close to the nuclear magneton (5.05 10 À27 JT À1 ), that is,1 840 times smaller than in the paramagnetic case.T o our great surprise,however, the Cl 2 ,Br 2 and I 2 halogen gases or vapors,when kept in the magnetic field, exhibited astrong ROAs ignal as w...
Previously, we and other laboratories have reported an unusual and strong Raman optical activity (ROA) induced in solvents by chiral dyes. Various theories of the phenomenon appeared, but they were not capable of explaining fully the observed ROA band signs and intensities. In this work, an analysis based both on the light scattering theory and dedicated experiments provides a more complete understanding. For example, double‐cell magnetic circular dichroism and magnetic ROA experiments with copper‐porphyrin complex show that the induced chirality is observed without any contact of the solvents with the complex. The results thus indicate that a combination of electronic circular dichroism (ECD) with the polarized Raman scattering is responsible for the effect. The degree of circularity of solvent vibrational bands is a principal molecular property participating in the event. The insight and the possibility to predict the chirality transfer promise future applications in spectroscopy, chemical analysis and polarized imaging.
Resonance Raman optical activity (RROA) possesses all aspects of a sensitive tool for molecular detection, but its measurement remains challenging. We demonstrate that reliable recording of RROA of chiral colorful compounds is possible, but only after considering the effect of the electronic circular dichroism (ECD) on the ROA spectra induced by the dissolved chiral compound. We show RROA for a number of model vitamin B 12 derivatives that are chemically similar but exhibit distinctively different spectroscopic behavior. The ECD/ROA effect is proportional to the concentration and dependent on the optical pathlength of the light propagating through the sample. It can severely alter relative band intensities and signs in the natural RROA spectra. The spectra analyses are supported by computational modeling based on density functional theory. Neglecting the ECD effect during ROA measurement can lead to misinterpretation of the recorded spectra and erroneous conclusions about the molecular structure.
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