Boris F. Kim

Gamma radiation resistance of the high Tc superconductor YBa2Cu3O7−δ

Exposure of the high Tc superconductor YBa2Cu3O7−δ to 60Co γ irradiation up to 1.3 Mrad is found to have virtually no effect on its superconductive properties as measured by a novel variant of the microwave absorption method.

Matrix isolation spectroscopy in methane. Isotropic ESR spectrum of HC17O

The isotropic electron spin resonance (ESR) spectrum of HC17O has been observed in methane at 20 K (prepared by photolysis of HI in CH4 containing 1% of 17O enriched CO), and the isotropic oxygen hyperfine splitting determined [a0(HCO)=−15.1 G]. Isotropic spectra of HO2 (prepared similarly with O2 replacing CO) and NO2 in methane were also observed. Superhyperfine interactions in the ESR spectrum of H atoms in CH4 indicate H is trapped in the octahedral interstitial site of the matrix. ‘‘Forbidden’’ proton spin‐flip transitions in the ESR spectrum of CH3 in methane indicate it is trapped at a substitutional site in the matrix.

Low temperature optical spectra of Zn porphin in triphenylene

The low temperature optical absorption spectra of single crystals of triphenylene doped with Zn porphin have been observed in detail. The spectra consisted of sharp lines, many of which were polarized. This is thought to be the first direct observation of polarized sharp line spectra of a porphyrin. Also observed were a number of weak anomalous absorption lines near the 0–0 transition, but at longer wavelengths. Two different site models were proposed to account for the polarization properties of the spectra. The implication of these results in the interpretation of porphyrin spectra are discussed.

Reactions of thermal hydrogen atoms in ethane and propane at 10 K: Secondary site selectivity in hydrogen abstraction from propane

The reactions of hydrogen atoms, generated by ultraviolet photolysis of hydrogen iodide, with solid ethane and propane at 10 K are investigated using electron spin resonance (ESR) to identify the reaction products. Although the results are generally similar to those found by others for these tunneling hydrogen abstraction reactions in dilute solutions of the alkanes in xenon, there also are significant differences, most notably, evidence that only the secondary hydrogen of propane is abstracted in its tunneling reaction with an H atom. Also notable is the high degree of crystalline order in the ethane matrix, which is preserved in the ethyl radical product of the H atom–ethane reaction.

Optical spectra of Cu porphin and VO porphin in single crystal triphenylene

Abstract Polarized optical absorption spectra of copper porphin and vanadyl porphin in single crystals of triphenylene have been obtained at room temperature, 77°K and 4.2°K. Luminescence spectra of these samples are also reported. The gross features of the spectra of these two metalloporphins are similar but the spectral lines in vanadyl porphin are much sharper than those in copper porphin, revealing much more satellite structure. It is shown that the central metal can substantially affect metalloporphyrin absorption spectra, contrary to the case of broad band solution spectra. The data is consistent with porphin molecules in substitutional sites of triphenylene and a crystal field reduction of the usual D 4 h metalloporphyrin symmetry to D 2 h .

Low-temperature optical absorption spectra of hematoporphyrins☆

Abstract Low-temperature optical absorption spectra of both free base and metal complexes of hematoporphyrin have been obtained. Vibrational structure, inferred by others from MORD data, is observed here directly in bands III and IV of the free base. Structure is also observed in the β band of the Ni and Pd metallohematoporphyrins. Implications of these results on the presently accepted theory of porphyrin optical spectra are discussed.

Optical spectra of Ni porphin, Pd porphin and free base porphin in single crystal triphenylene☆

Abstract Polarized optical absorption spectra and luminescence spectra of palladium porphin, nickel porphin, and porphin free base doped into triphenylene host crystals have been obtained. The d 8 metalloporphin spectra obtained here allow a comparison to be made with other metalloporphin spectra reported previously from this laboratory and suggest a general description of the polarized absorption spectra of metalloporphins in this host. The observation of many spectral lines which occur at the same wavelength in absorption and fluorescence suggests that band I of free base porphin may be of greater complexity than previously thought.

An ESR study of vanadyl porphin

Abstract We report the first ESR spectra of the unsubstituted vanadyl porphyrin. The ESR spectra of vanadyl porphin in its magnetically concentrated form, in a tetrahydrofuran solution, in polycrystalline triphenylene, and in single-crystal triphenylene have been obtained. The hyperfine structure which was observed in vanadyl tetraphenylporphin was not seen in vanadyl porphin, indicating increased dipolar interactions. The data is consistent with porphin molecules in substitutional triphenylene sites, a fact which was not apparent from previous optical studies. The observation of the sample dependence of the number of ESR sites remains as an unexplained anomaly.

Magnetic behavior of both superconducting thin films and their deposition targets

The superconducting properties of the bulk oxides La1.85Sr0.15CuO4−x and Ba2YCu3O7−y were investigated through their magnetic behavior by vibrating‐sample magnetometry and complex ac susceptibility, and by dc resistivity and microwave response. These oxides were then used as targets in the preparation of thin films using a laser‐ablation technique. The superconducting properties of the films were established through their microwave response. The M‐H loops at low temperatures clearly establish the type‐II behavior of the Ba‐Y‐Cu‐O materials. The real part of the ac susceptibility showed the superconducting transition. Simultaneously, the imaginary part of the ac susceptibility showed the existence of nonsuperconducting portions in the samples which have a low enough resistivity to carry a significant amount of current. The novel method of microwave response was used to detect the superconductivity for both the bulk oxides and the thin films.

Anomalous temperature‐dependent phosphorescence of Cu porphin in anthracenea)

The temperature dependence of the phosphorescence spectrum of copper porphin in anthracene has been studied from room temperature down to 8 K and the 4.2 K spectrum has been obtained. A 23.4 cm−1 crystal field splitting of the orbital components of the TQ state was observed. The 0–0 transition appears abruptly at approximately 25 K and increases rapidly in intensity as the temperature is lowered. A model involving energy transfer from the copper porphin to the triplet exciton band of anthracene gives a satisfactory explanation for the anomalous temperature dependence of the copper porphin phosphorescence intensity.