Laser‐Induced Crystallization and Crystal Growth

Recent streams of laser studies on crystallization and crystal growth are summarized and reviewed. Femtosecond multiphoton excitation of solutions leads to their ablation at the focal point, inducing local bubble formation, shockwave propagation, and convection flow. This phenomenon, called “laser micro tsunami” makes it possible to trigger crystallization of molecules and proteins from their supersaturated solutions. Femtosecond laser ablation of a urea crystal in solution triggers the additional growth of a single daughter crystal. Intense continuous wave (CW) near infrared laser irradiation at the air/solution interface of heavy‐water amino acid solutions results in trapping of the clusters and evolves to crystallization. A single crystal is always prepared in a spatially and temporally controlled manner, and the crystal polymorph of glycine depends on laser power, polarization, and solution concentration. Upon irradiation at the glass/solution interface, a millimeter‐sized droplet is formed, and a single crystal is formed by shifting the irradiation position to the surface. Directional and selective crystal growth is also possible with laser trapping. Finally, characteristics of laser‐induced crystallization and crystal growth are summarized.     

Excitation wavelength dependent surface-enhanced Raman spectra of a dipping film of azobenzene-containing long-chain fatty acid on a silver mirror

Surface-enhanced Raman scattering (SERS) of dipping films of azobenzene-containing long-chain fatty acids, nAmH (n=8, 12, m=3, 5), on silver mirrors measured with a wide range of excitation wavelengths in the 457.9-1064 nm region is reported. The obtained Raman spectra show great SERS effect even with the 1064 nm excitation, and the excitation with 457.9, 476.5, and 488.0 nm gives surface-enhanced resonance Raman scattering (SERRS) due to the resonance effect of the symmetry-forbidden n-pi* transition of the azo group. Of particular note in the present study is that the SERS spectra with the excitation in the 532-1064 nm region yield Raman bands whose frequencies are almost identical to those bands in Raman spectra of nAmH in solid state while the SERRS spectra with the excitation in the 457.9-514.5 nm region show not only a set of bands which correspond to those of nAmH in the solid state but also a set of bands whose frequencies show a significant shift from those of the bands of nAmH in the solid state. These observations lead us to conclude that there are two kinds of molecular aggregates in the dipping films of azobenzene-containing long-chain fatty acid in which azobenzene moieties are condensed to form small bundles.     

Characterizing Higgs portal dark matter models at the ILC

We study the dark matter (DM) discovery prospect and its spin discrimination in the theoretical framework of gauge invariant and renormalizable Higgs portal DM models at the ILC with \(\sqrt{s} = 500\) GeV. In such models, the DM pair is produced in association with a Z boson. In the case of the singlet scalar DM, the mediator is just the SM Higgs boson, whereas for the fermion or vector DM there is an additional singlet scalar mediator that mixes with the SM Higgs boson, which produces significant observable differences. After careful investigation of the signal and backgrounds both at parton level and at detector level, we find the signal with hadronically decaying Z boson provides a better search sensitivity than the signal with leptonically decaying Z boson. Taking the fermion DM model as a benchmark scenario, when the DM-mediator coupling \(g_\chi \) is relatively small, the DM signals are discoverable only for benchmark points with relatively light scalar mediator \(H_2\). The spin discriminating from scalar DM is always promising, while it is difficult to discriminate from vector DM. As for \(g_\chi \) approaching the perturbative limit, benchmark points with the mediator \(H_2\) in the full mass region of interest are discoverable. The spin discriminating aspects from both the scalar and the fermion DM are quite promising.     

Determining the dark matter relic density in the minimal supergravity stau-neutralino coannihilation region at the Large Hadron Collider

We examine the stau-neutralino coannihilation (CA) mechanism of the early Universe. We use the minimal supergravity (mSUGRA) model and show that from measurements at the CERN Large Hadron Collider one can predict the dark matter relic density with an uncertainty of 6% with 30 fb(-1) of data, which is comparable to the direct measurement by the Wilkinson Microwave Anisotropy Probe. This is done by measuring four mSUGRA parameters m(0), m(1/2), A(0), and tanbeta without requiring direct measurements of the top squark and bottom squark masses. We also provide precision measurements of the gaugino, squark, and lighter stau masses in this CA region without assuming gaugino universality.     

Radical polymerization of 4-methylene-4H-1,3-benzodioxin-2-ones: Cyclic α-substituted styrenes

4-Methylene-4H-1,3-benzodioxin-2-one (MBDOON), an α-substituted cyclic styrene derivative, was synthesized and polymerized readily with 2,2′-azobis(isobutyronitrile) (AIBN) as an initiator in solution. The kinetics of the MBDOON homopolymerization with AIBN was investigated in N-methyl-2-pyrrolidone (NMP). The rate of polymerization, R_p, can be expressed by R_p ? k[AIBN]^0.52[MBDOON]^1.1 and the overall activation energy has been calcualted to be 75.7 kJ/mol. Monomer reactivity ratios in copolymerization of MBDOON (M₂) with styrene (M₁) are r₁ = 0.31 and r₂ = 3.20, from which Q and e values of MBDOON can be calculated as 3.0 and ?0.7, respectively. Ring-substituted MBDOON monomers such as 6-chloro, 6-methyl, and 7-methoxy derivatives were synthesized and polymerized with AIBN. The 6-substituted MBDOON's readily underwent radical polymerization while the 7-methoxy-MBDOON was slower to polymerize. Poly(MBDOON) is predominantly heterotactic. (rr = 35, mr = 46, and mm = 19%). The polymer releases carbon dioxide at about 200°C and is converted with some depolymerization to poly[(o-hydroxyphenyl)acetylene]. The thermolysis temperature is very much affected by the ring substituent. The onset of carbon dioxide liberation was observed at 140°C in the case of the 7-methoxyl derivative while the 6-substituents had a smaller effect on the decarboxylation temperature. © 1993 John Wiley & Sons, Inc.     

Syntheses and properties of chiral pentahomothiazacalix[3]arenes

Chiral calixarene analogs incorporating an aminoethanethiol unit such as L-cysteine into their rings were prepared. Conformational analysis of the macrocycles by using ¹H and ¹³C nmr spectroscopy revealed that their preferred conformation was a cone, which was more stable in chloroform than in toluene. The introduction of an aminoethanethiol moiety into the macrocyclic ring caused ring fluctuation, however, the carboxylic acid derivative was a highly rigid structure in the cone form. The ¹H nmr and circular dichroism spectra of the macrocycles showed the existence of chirality of the phenol-formaldehyde unit, which was induced by the chirality of the cysteine moiety.