Magnetic Raman Optical Activity Research Articles

Diamagnetic Raman Optical Activity of Chlorine, Bromine, and Iodine Gases

AbstractMagnetic Raman optical activity of gases provides unique information about their electric and magnetic properties. Magnetic Raman optical activity has recently been observed in a paramagnetic gas (Angew. Chem. Int. Ed. 2012, 51, 11058; Angew. Chem. 2012, 124, 11220). In diamagnetic molecules, it has been considered too weak to be measurable. However, in chlorine, bromine and iodine vapors, we could detect a significant signal as well. Zeeman splitting of electronic ground‐state energy levels cannot rationalize the observed circular intensity difference (CID) values of about 10−4. These are explicable by participation of paramagnetic excited electronic states. Then a simple model including one electronic excited state provides reasonable spectral intensities. The results suggest that this kind of scattering by diamagnetic molecules is a general event observable under resonance conditions. The phenomenon sheds new light on the role of excited states in the Raman scattering, and may be used to probe molecular geometry and electronic structure.

Diamagnetic Raman Optical Activity of Chlorine, Bromine, and Iodine Gases.

Magnetic Raman optical activity of gases provides unique information about their electric and magnetic properties. Magnetic Raman optical activity has recently been observed in a paramagnetic gas (Angew. Chem. Int. Ed. 2012, 51, 11058; Angew. Chem. 2012, 124, 11220). In diamagnetic molecules, it has been considered too weak to be measurable. However, in chlorine, bromine and iodine vapors, we could detect a significant signal as well. Zeeman splitting of electronic ground-state energy levels cannot rationalize the observed circular intensity difference (CID) values of about 10(-4). These are explicable by participation of paramagnetic excited electronic states. Then a simple model including one electronic excited state provides reasonable spectral intensities. The results suggest that this kind of scattering by diamagnetic molecules is a general event observable under resonance conditions. The phenomenon sheds new light on the role of excited states in the Raman scattering, and may be used to probe molecular geometry and electronic structure.

Exploring Raman optical activity for transition metals: From coordination compounds to solids

We briefly review the field of Raman optical activity (ROA) for transition-metal containing systems with a focus on coordination compounds and solids. In contrast to ROA measurements for optically active solids, ROA for chiral metal complexes is a relatively novel field with only a few measurements and calculations published yet. Their results indicate a great sensitivity of ROA for the elucidation of such compounds, even in case of structurally very similar geometrical isomers, and the differentiation of several types of chirality. Resonance with one or more electronic transitions can lead to intensity enhancement in the ROA spectrum, which provides additional advantages such as shorter measurement times, lower sample amounts and valuable information about involved excited electronic states. A widely unknown variant is magnetic ROA where an external magnetic field is applied. This form is applicable to both chiral and achiral systems and has, among others, been employed to probe Zeeman splittings and sign of g factors. This review shows that ROA is a very promising field for in-depth study and design of transition-metal containing compounds and materials. It is still in its infancy and possible next steps for future research, with an emphasis on computational developments, are outlined.

Magnetic Raman optical activity in FeF 2

Raman optical activity (ROA) of magnons and phonons in antiferromagnetic FeF 2 ( T N=78 K) has been studied as a function of temperature and in applied magnetic field. For exciting light incident along the rutile-structure c-axis, ROA is observed for magnons but not phonons. In zero field, the small anisotropy-induced splitting (0.09 cm −1) of the two acoustic-magnon branches is observed by light scattering for the first time. The splitting in applied magnetic field is found to reduce with increasing temperature in accordance with theory. No ROA was detected for two-magnon excitations.

Instrument for natural and magnetic Raman optical activity studies in right‐angle scattering

AbstractA simple computer‐controlled instrument for natural and magnetic incident circular polarization Raman optical activity (ICP ROA) measurements in right‐angle scattering is described. The key spectral elements consist of a fast single‐stage monochromator equipped with a holographic notch filter, a highly efficient holographic diffraction grating and a thinned back‐illuminated, thermoelectrically cooled charge‐coupled device (CCD) detector. A temperature‐stabilized longitudinal electro‐optic modulator is employed to switch between orthogonal circular polarization states in the incident laser radiation. A polaroid film together with a mica half‐wave retardation plate are used to select particular linear polarization states in the Raman scattered radiation with the same instrumental response. High‐quality depolarized and polarized Stokes and depolarized anti‐Stokes ICP ROA spectra of (R)‐(−) and (S)‐(+)‐phenyloxirane and depolarized magnetic resonance ICP ROA spectra of copper(II) tetrabromide are presented as typical examples of the excellent performane characteristics.

Magnetic Raman optical activity and Raman electron paramagnetic resonance

Abstract

On the theory of the dominant artefacts in natural and magnetic Raman optical activity

AbstractThe molecular theory of the scattering of polarized light is applied to the problem of the artefacts that frequently arise in Raman circular intensity difference measurements. By including the effect of the finite solid angle in the cone of collected light, a detailed understanding of the major sources of artefacts in polarized and depolarized measurements, and their dependence on the polarization characteristics of the Raman band, is obtained. Inclusion of both antisymmetric and symmetric scattering contributions reveals why magnetic are usually less susceptible to artefacts than natural Raman optical activity spectra.

Magnetic electronic Raman optical activity of osmium (IV) hexabromide, iridium (IV) hexachloride and uranocene

AbstractMagnetic optical activity is reported in electronic resonance Raman transitions of OsBr, IrCl and U(C8H8)2 in solution. All the effects are observed in the form of couplets which originate in separate Raman transitions between magnetic components of the initial and final levels. These can give detailed information about the magnetic structure of the ground and low‐lying electronic states, particularly the sign of the g‐factor and the ordering of magnetic sub‐states in general. For example, effects in the 466 cm−1 electronic Raman band of U(C8H8)2 confirm that the MJ = ±4 level lies below the MJ = ±3 level. We also use the magnetic Raman optical activity to identify a very weak U(C8H8)2 Raman band at 675 cm−1 with a vibrational‐electronic combination transition.

Anti-stokes magnetic Raman optical activity and time reversal

Anti-stokes magnetic Raman optical activity and time reversal

Anti-stokes magnetic Raman optical activity and time reversal

Time-reversal arguments are used to relate the sign of the magnetic Raman optical activity in corresponding Stokes and anti-Stokes bands in the two distinct cases of a system with an odd and an even number of electrons. Observations on IrCl 2− 6 are reported which confirm some of the predictions.

Sign of theg-value in IrCl62−using magnetic circular dichroism data A correction of the suggestion by Barronet al

It is explicitly shown that the sign of the ground state g-value of IrCl6 2− was correctly calculated in earlier MCD work and that the sign recently deduced from magnetic Raman optical activity measurements agrees with this calculation. This refutesa recent suggestion by Barron et al. that a considerable body of spectroscopic assignments are thrown into doubt because this sign was incorrectly assumed in the earlier work. It is also shown that the MCD pattern in IrCl6 2− permits a correct dectuction of the sign of the ground state g-value.

Magnetic vibrational optical activity in the resonance Raman spectrum of ferrocytochrome c

The first observations of magnetic Raman optical activity are reported. Using a field of about 0.7T, Raman circular intensity differentials up to ±4×10−3 are induced in resonance Raman bands of ferrocytochrome c.