Circularly polarised light

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. 

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

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. 

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 ... 

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-... 

CPL circularly polarised light CSA camphorsulphonic acid IR infrared... 

Ae In circular dichroism, amplitude of the CD maximum difference in molar absorption coefficients for right and left circularly polarised light. May be positive or negative. 

Many biologically interesting chromophores are chiral, or optically active, which means that they absorb right and left circularly polarised light to differing degrees. 

The operation of a GaAs source is shown schematically in fig 2.12. Right-hand (or left-hand) circularly-polarised light is incident on a negative-affinity GaAs crystal. The negative affinity is achieved by coating the... 

The cycloaddition of the allenes (63) to cyclopentenone results in the formation of the two adducts (64) and (65) in a ratio of 4 1. The addition reaction occurs primarily across the less substituted double bond of the aliens. Cycloaddition of acetylene and but-l-yne to the enones (66) can be brought about using left-circularly polarised light. The resultant cyclobutane derivatives are readily converted to the optically active enones (67). The photoaddition of hex-1-yne to the lactone (68) affords the two isomeric adducts... 

More recent experiments by Walker et al. [37] using linearly and circularly polarised light and ion TOP spectroscopy confirmed the existence of the knee but, more importantly, electron-ion and electron-electron coincidence experiments were performed. Using the electron-ion coincidence technique, it was found that the great majority of the Xe ions were produced in a sequential process. Moreover, direct double ionization was not observed in these electron-electron coincidence experiments. Charalambidis et al. [38] considered this long-standing question of direct double ionization in Xe and also concluded that it does not occur. That does not mean that correlated double emission cannot occur under appropriate conditions. 

The phenomenon of differences between the absorption of left- and of right-circularly polarised light is not restricted to the visible and UV wavelength regions, so infrared and Raman CD are likely to yield even more sophisticated information... 

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