Observations of surface modifications induced by the multiple pulse irradiation using a soft picosecond x-ray laser beam

To study the interactions between picosecond soft x-ray laser (SXRL) beams and material surfaces, gold (Au), copper (Cu), and silicon (Si) surfaces were irradiated with SXRL pulses having a wavelength of 13.9 nm and a duration of ～7 ps. Following irradiation, the surfaces of the substrates were observed using a scanning electron microscope and an atomic force microscope. With single pulse irradiation, ripple-like structures were formed on the Au and Cu surfaces. These structures were different from previously investigated conical structures formed on an Al surface. In addition, it was confirmed that the development of modified structures, i.e., growth of hillocks on the Au and Cu surfaces, was observed after multiple SXRL pulse exposures. However, on the Si surface, deep holes that seemed to be melted structures induced by the accumulation of multiple pulses of irradiations were found. Therefore, it was concluded that SXRL beam irradiation of various material surfaces causes different types of surface modifications, and the changes in the surface behaviors are attributed to the differences in the elemental properties, such as the attenuation length of x-ray photons.     

Class number parity for cyclotomic fields

We give a simple criterion for the parity of the class number of the cyclotomic field.

     

Intermolecular coupling of alkynes, isocyanates, and acyl chlorides: an efficient method for the synthesis of 5-hydroxypyrrol-2(5H)-ones

New insights into the reaction of diethylzirconocene with an alkyne, an isocyanate, and an acyl chloride in this order are reported. The products of 5-hydroxypyrrol-2(5H)-ones are obtained in good yields after hydrolysis. It is an efficient method for the synthesis of 5-hydroxypyrrol-2(5H)-ones.     

A three carbon homologation by the ring-opening of β-propiolactones with diorganocuprates

Various organocuprates react with β-propiolactones to give β-substituted propionic acids in high yields.     

Crystal structure of polyisobutylene

The crystal structure of polyisobutylene was determined by x-ray analysis. The orthorhombic cell, with a = 6.88 Å, b = 11.91 Å, c (fiber axis) = 18.60 Å (space group: P2₁2₁2₁ ? D), contains two molecular chains each consisting of eight monomeric units in the fiber identity period. The chain conformation is essentially an (8/3) helix, but deviates appreciably from the exact (8/3) helix symmetry. The symmetry of the molecular chain is only a twofold screw axis in exact sense, and a crystallographic asymmetric unit consists of four monomeric units. The torsional angles are where M denotes the methyl group. The averaged skeletal C? CH₂? C and C? CM₂? C bond angles are 128° and 110°, respectively. The large C? CH₂? C bond angles may be due to steric respulsion between the adjacent methyl groups, giving intramolecular distances larger than 3.09 Å.     

Effects of a magnetic field on triplet-triplet annihilation in a Pt-phthalocyanine single crystal at 4.2 K

Mutual annihilation of triplet excitons in Pt-phthalocyanine single crystal at 4.2 K has been studied under magnetic fields of up to 100 kG through the measurement of the phosphorescence decay by Q-switched ruby laser excitation. The maximum annihilation rate γ which is larger than that of zero magnetic field by 40–50% is obtained at magnetic fields of 30–40 kG. The annihilation rate γ is of the order of 10⁻¹² cm³/s.     

Photoluminescence of cis- and trans-polyacetylene

The emission intensity in cis-(CH)_χ increases a little and the emission peak shifts a little to shorter wavelength with increasing temperature, which can be interpreted by the distribution of several emission centers in energy. Photoluminescence is also observed in trans-(CH)_χ at around 1.03 μm for the first time.     

Hadroproduction of heavy quark flavors in QCD

Within the framework of perturbative QCD, we investigate the hadroproduction of charmed particles via two-gluon as well as quark-pair annihilation. The total production cross section is found to be sensitive to the choice of the scale parameter Q² and in general not free from non-perturbative effects. Charmed-particle production in the high-p_T region is also studied.