Polarisation circular

Magneto-optical activity results from the asymmetry in the indices of refraction for the left (—) and right (+) hand polarised circular components of a light wave induced in a medium by a longitudinal B field. It subdivides as shown in table 4.2. 

The question also arises as to where the chiral molecules came from. Were the L-amino acids or the D-sugars selected on the primeval Earth, or are exuaterresuial sources responsible for the homochirality This second possibility is dealt with by hypotheses on the effect of circularly polarised light, of extraterrestrial origin, on chiral molecules in the molecular clouds from which the solar system was formed. One such hypothesis was proposed by Rubenstein et al. (1983) and developed further by others, particularly A. W. Bonner (Bonner and Rubenstein, 1987) both scientists worked at Stanford University. The authors believe that the actual radiation source was synchrotron radiation from supernovae. The excess of one enantiomeric form generated by this irradiation process would have needed to be transported to Earth by comets and meteorites, probably during the bombardment phase around 4.2-3.8 billion years ago. 

This hypothesis has shared the same fate as many others on the biogenesis problem it is still in dispute Not only is the origin of the circularly polarised (CP)... 

Laboratory data from two groups (see Sect. 3.2.4) indicate that chiral amino acid structures can be formed in simulations of the conditions present in interstellar space. The experimental results support the assumption that important asymmetrical reactions could have taken place on interstellar ice particles irradiated with circularly polarised UV light. The question as to whether such material was ever transported to the young Earth remains open. But the Rosetta mission may provide important answers on the problem of asymmetric syntheses of biomolecules under cosmic conditions (Meierhenrich and Thiemann, 2004). 

For the dichroic photolysis mechanism to be successful, amino acids must be synthesised and destroyed in an intense circularly polarised radiation field. Daylight shows little or no excess but recent observations at 2.2 /rm of the Orion reflection nebula OMC-1 shows polarisations in excess of 17 per cent, although... 

A particular case is "absolute asymmetric induction" which requires a chiral physical force-such as circularly polarised light- rather than a chiral chemical reagent. 

The spectmm from an undulator is very different, and numerous peaks result from interference effects within the undulator. When the electron acceleration is confined to the orbit plane and the emission angle very low, the radiation is strongly elliptically polarised and, in the orbit plane itself, it is to within a few per cent linearly polarised. Use of a sequence of permanent magnets with magnetisation arranged in a spiral sequence enables circularly polarised radiation to be extracted from such a helical undulator and this radiation is particularly important for magnetic studies. 

Linear dichroism data with DNA oriented by an electric field [53, 54] or a linear flow [55, 56], under linearly polarised light, lead to determinations of the angle between the absorbing transition dipole moment of the chromophore in the molecule and the DNA helix axis conclusions concerning intercalation may thus be drawn from this technique. Finally, with chiral compounds, circular dichroism is also an attractive method to determine the enantioselectivity in the binding of the molecule [48, 57,58]. 

Chiral molecules possess the unique property of interacting differentially with left and right circularly polarised light. A differential absorption is known as... 

Note 3 Chiral nematic mesophases exhibit Bragg scattering of circularly polarised light at a wavelength proportional to the pitch P (Xr = P, where is the mean refractive index). 

Note 4 A BP is optically isotropic and exhibits a Bragg reflection of circularly polarised light. 

If the incoming light is polarised, any chiral features of the molecule that absorbs will be highlighted—in particular changes in such chiral features, e.g. when the protein is unfolding, these features will stand out. The secondary stmctural elements of proteins are chiral in their nature. This phenomenon can be followed with the so-called circular dichroism (CD). ... 

Gadsden, M., P. Rothwell, and M. J. Taylor, 1979. Detection of circularly polarised light from noctilucent clouds, Nature, 278, 628-629. 

The origin of the n2 measured using the 10 ns pulses could be electronic or molecular rotation. These can be distinguished by measuring the ratio of the critical power for self-focusing for linear and circular polarised light. The observed ratio of 2.1 is consistent with a molecular rotation (11-13.161 and relates to the anisotropic polarisability of the molecule. The rotational relaxation time, calculated from the Debye formula (H), is about 0.5-2 ns, consistent with these results. 

The superscripts, 1 and c, in Table I identify linear and circular polarised light respectively. Since the nanosecond measurements were dominated by molecular rotation in the dithiolene complexes, degenerate four wave mixing measurement were carried out using 100 ps pulses to measure the electronic contribution directly. 

The extent of rotation is proportional to the difference of the refractive indices for the right and left circularly polarised light ... 

Unlike ORD, circular dichroism (CD) depends upon the differential absorption of the two circularly polarised part-beams of incident light by an optically active compound. The combined action of anomalous ORD and CD is summarised as the Cotton effect. Therefore Cotton effects can be determined both... 

In right- or left circularly polarised light, the tip of the electrical field vectors describes a helix in a clockwise or anticlockwise sense, respectively. 

Linearly polarised light can be understood as the superposition of two circularly polarised light rays of the same frequency, velocity, and amplitude (inten-... 

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