No abstract

Mixing of powdered (؊)-and (؉)-enantiomer crystals in the solid state gives crystals of the racemic compound. This racemic crystal formation was followed by IR spectral measurement of a 1 : 1 mixture of (؊)-and (؉)-enantiomer crystals as a Nujol mull. As the formation of racemic crystals proceeds, the OH absorptions of the enantiomer disappear gradually and new OH absorptions due to the racemic compound appear. The formation of racemic crystals from enantiomer crystals has been studied for various kinds of chiral compounds: 2,2Ј-dihydroxy-1,1Ј-binaphthyl (1) and its derivatives, 10,10Ј-dihydroxy-9,9Ј-biphenanthryl (4), 2,2Ј-dihydroxy-4,4Ј,6,6Ј-tetramethylbiphenyl (5)

We report that the optical polarization in the afterglow of GRB 091208B is measured at t = 149 − 706 s after the burst trigger, and the polarization degree is P = 10.4% ± 2.5%. The optical light curve at this time shows a power-law decay with index −0.75 ± 0.02, which is interpreted as the forward shock synchrotron emission, and thus this is the first detection of the early-time optical polarization in the forward shock (rather than that in the reverse shock reported by (Steele et al. 2009)). This detection disfavors the afterglow model in which the magnetic fields in the emission region are random on the plasma skin depth scales, such as amplified by the plasma instabilities, e.g., Weibel instability. We suggest that the fields are amplified by the magnetohydrodynamic instabilities, which would be tested by future observations of the temporal changes of the polarization degrees and angles for other bursts.

Noncentrosymmetic and chiral cocrystals were prepared from 2-amino-3-nitropyridine (2A3NP) and achiral benzenesulfonic acids (Ar-SO 3 H), which were designed for second-order nonlinear optical materials. Both components are commonly crystallized in 1:1 ionic forms of 2A3NPH + ‚Ar-SO 3 -. The molecular packings of cocrystals are controlled by the aromatic-aromatic interactions as well as multidirectional ionic and hydrogen bonds between the 2A3NPH + cations and the sulfonate anions. The crystal of 2A3NP with p-toluenesulfonic acid belongs to acentric space group Pna2 1 , in which 2A3NPH + cations and anions are alternately stacked with some dihedral angle due to the large sulfonate anions to form two independent column structures in a perpendicular direction to each other. The crystal of 2A3NP with p-nitrobenzenesulfonic acid crystallizes into chiral space group P2 1 2 1 2 1 . The 2A3NPH + cations and the anions are also alternately stacked to give herringbone network of 2A3NPH + cations. The crystal of 2A3NP with 2,5-dimethylbenzenesulfonic acid belongs to acentric space group Pn, in which two independent stacking structures are formed in perpendicular directions. Second-harmonic generation (SHG) power measured with an evanescent wave technique revealed the relatively high SHG efficiency of cocrystal of 2A3NP with p-toluenesulfonic acid, 2-fold larger than that of well-known m-nitroaniline.

We presented optical and near-infrared multi-band linear polarimetry of the highly reddened Type Ia SN 2014J appeared in M82. SN 2014J exhibits large polarization at shorter wavelengths, e.g., 4.8% in B band, and the polarization decreases rapidly at longer wavelengths, with the position angle of the polarization remaining at approximately 40 • over the observed wavelength range. These polarimetric properties suggest that the observed polarization is likely to be caused predominantly by the interstellar dust within M82. Further analysis shows that the polarization peaks at a wavelengths much shorter than those obtained for the Galactic dust. The wavelength dependence of the polarization can be better described by an inverse power law rather than by Serkowski law for Galactic interstellar polarization. These suggests that the nature of the dust in M82 may be different from that in our Galaxy, with polarizing dust grains having a mean radius of < 0.1 µm .