Bong Hyun Boo

Distribution and characteristics of 239,240Pu and 137Cs in the soil of Korea

The concentrations of 239,240Pu and 137Cs were determined in undisturbed surface soil (0–4 cm) in Korea. They were in the range of 0.24~1.1 Bq kg−1 and 12.4~55.6 Bq kg−1, respectively. The mean activity ratio of 239,240Pu137Cs in soil was 0.0224, which is very similar to the estimated value (0.0211) commonly attributed to the atmospheric nuclear test. The influence of rainfall on the deposition of 239,240Pu and 137Cs, and the effect of organic matter content, clay content and pH on the relative adsorption of the two radionuclides on the surface soil were studied using the field method. Among parameters affecting the cumulative deposition of the radionuclides, the organic matter content plays the most important role in the retention and relative mobility of 239,240Pu and 137Cs in the soil. The other parameters such as rainfall, clay content and pH were of less significance.

Second molecular hyperpolarizability of 2,2′-diamino-7,7′-dinitro-9,9′- spirobifluorene: An experimental study on third-order nonlinear optical properties of a spiroconjugated dimer

Nonlinear optical properties of a fixed molecular dimer, 2,2′-diamino-7,7′-dinitro9,9′-spirobifluorene (ANSF), have been investigated in solution by the degenerate four-wave mixing technique. It has been observed that the orientationally averaged second molecular hyperpolarizability of ANSF in THF is enhanced ten times in comparison with its monomer unit, 2-amino-7-nitrofluorene. Since electronic coupling between monomer units in ANSF is negligible owing to symmetry, we attribute the large enhancement to the orientational effect of the two constituting dipoles with possible involvement of vibronic coupling and spiroconjugation.

Depth distribution of239,240Pu and137Cs in soils of South Korea

Depth distribution of239,240Pu and137Cs in the soils of South Korea have been studied. The average accumulated depositions were estimated roughly to be 54.8±32.1 Bq·m−2 for239,240Pu, 1.6±1.0 Bq· ·m−2 for238Pu and 1982.8±929.1 Bq·m−2 for137Cs. The activity ratios of239,240Pu/137Cs in soils were found to be in the narrow range of 0.0153 to 0.0364 with a mean value of 0.0230±0.006. The concentrations of239,240Pu and137Cs in soils decrease exponentially with increasing the soil depth. A significant correlation was found between the concentration of239,240Pu and that of137Cs. The activity ratios of239,240Pu/137Cs tend to increase slightly with increasing soil depth.

Theoretical investigations for the molecular structures and binding energies for C6H6(H2O) n , (n = 1–7) complexes

The geometrical parameters, vibrational frequencies, and dissociation energies for (H2O) n and C6H6(H2O) n (n = 1–7) clusters have been investigated using density functional theory (DFT) with various basis sets. The highest levels of theory employed are B3LYP/aug-cc-pVTZ for optimization and MP2/aug-cc-pVTZ//B3LYP/aug-cc-pVTZ for binding energy. The harmonic vibrational frequencies and IR intensities are also determined at the various levels of theory to confirm whether the hydrogen-bonded structure of water complex (W n , n = 1–7) is affected by the presence of benzene. The effect of benzene on the OH stretch modes of benzene–water complex (BW n , n = 1–7) is observed in the π-hydrogen bonded OH stretch. For each of the BW n clusters the intensity of this mode is increased significantly due to charge transfer/polarization interactions and the frequency shifts from W n to BW n are in the range of 40–60 cm−1. The calculations give the binding energies of 2.58, 4.20, 3.27, 3.00, 3.42, 4.14, and 5.49 kcal/mol for BW1–BW7, respectively after ZPVE and 50%-BSSE corrections.

Pulsed laser deposition of nanocrystalline ZnSe:N thin films

We have grown nanocrystalline ZnSe thin films on GaAs(100) substrates by pulsed laser deposition using a KrF excimer laser. Atomic force microscopy shows that the ZnSe thin films grown on GaAs(100) at 10−1 Torr are flat and dense and are composed of crystallites with an average roughness of 1–2 nm. X-ray diffraction results indicate that crystallites of these ZnSe thin films are of (100) crystalline orientation with an average size of about 10–30 nm. X-ray photoelectron spectroscopy indicates that the as-deposited thin films contain 5–7% [N], and nitrogen with N–Zn bondings includes about 40–60% of the total contained nitrogen. Photoluminescence measurements show a donor-to-acceptor pair recombination emission, which reveals the activation of [N] atoms as shallow acceptors in nanocrystalline ZnSe.

Spectroscopic and AM1 semiempirical studies of vibrations of tris(trimethylsilyl)silane derivatives, (Me3Si)3SiX (X H, Cl, OH, OD, Me, OMe, SiMe3)

Abstract The title compounds were synthesized and characterized. The vibrational frequencies of (Me 3 Si) 3 SiX (X  H, Cl, OH, OD, Me, OMe, SiMe 3 ) were determined by means of IR and Raman spectroscopy. Based on our AM1 semiempirical calculation and the literature group frequencies of CH 3 , Me 3 Si, SiSi 3 , SiX (X  H, Cl, OH, OD, CH 3 , OCH 3 ) have been assigned. The intensities of the Raman lines of the stretching vibrations of (Me 3 Si) 3 SiX (X  Cl, OH, OMe) and (Me 3 Si) 3 SiOH are very low compared with those of the IR lines. This indicates that the bonds have a strong ionic nature.

Dissociative multiple photoionization of Br2, IBr, and I2 in the VUV and X-ray regions: a comparative study of the inner-shell processes involving Br(3d,3p,3s) and I(4d,4p,4s,3d,3p)

Abstract Dissociative multiple photoionization of the bromine, the iodine monobromide, and the iodine molecules in the Br(3d,3p,3s) and I(4d,4p,4s,3d,3p) inner-shell regions has been studied by using time-of-flight (TOF) mass spectrometry coupled to synchrotron radiation in the ranges of 90∼978 eV for Br 2 , 60∼133 eV for IBr, and 86∼998 eV for I 2 . Total photoion and photoion–photoion coincidence (PIPICO) yields have been recorded as functions of the photon energy. Here, giant shape resonances have been observed beyond the thresholds of the inner-shells owing to the Br(3d 10 )→Br(3d 9 ϵ f), I(4d 10 )→I(4d 9 ϵ f), and I(3d 10 )→I(3d 9 ϵ f) transitions. The dissociation processes of the multiply charged parent ions have also been evaluated from variations of photoelectron–photoion coincidence (PEPICO) and PIPICO spectra with the photon energy. From each Br(3p 3/2 ) (189.9 eV) and I(4p 3/2 ) threshold (129.9 eV), quintuple ionization of the molecules begins to play important roles in the photoionization, subsequently yielding ion pairs of X 3+ –X 2+ (X=Br, I). From the I(3d 5/2 ) threshold (627.3 eV), loss of six electrons from iodine molecule additionally begins to play a minor role in the multiple photoionization, giving rise to the formation of ion pairs of either I 3+ –I 3+ or I 4+ –I 2+ . A direct comparison of the strengths and the ranges of the I(4d) and Br(3d) giant resonances was successfully made from dissociative photoionization of IBr. Over the entire energy range examined, 60 E

Growth of ZnSe:N epilayers by pulsed laser ablation deposition

Epilayers of nitrogen doped ZnSe have been grown on GaAs(100) substrates by pulsed laser ablation deposition assisted by a nitrogen beam produced by a supersonic nozzle beam source. X-ray photoelectron spectroscopy (XPS) shows that the epilayers are composed of 83.8% Zn and Se, 10.4% N and 5.8% O, and other kinds of impurity are rare. XPS spectra of Zn(2p3/2 ) and N(1s) core levels indicate that doped nitrogen with an estimated concentration of over 1021 cm-3 exists in the as-grown epilayer. Atomic force microscopy indicates that the surface of an as-grown ZnSe epilayer on GaAs(100) is flat with roughness of about 1.2 nm, which is less than that of some good-quality metalorganic vapour phase epitaxy grown layers. X-ray diffraction results show that these ZnSe epilayers are a characteristic of single crystallinity.

Theoretical and jet spectroscopic investigations of energetics and structures for the low-lying singlet states of fluorene and 9,9′-spirobifluorene

Abstract Ab initio, semiempirical and spectroscopic studies of fluorene (FR) and 9,9′-spirobifluorene (SBF) were performed to elucidate π-orbital interaction between two fluorenyl rings of SBF and to predict the energies of the low-lying singlet electronic states of the molecules. Energies and symmetries of π-orbitals of FR and SBF molecules were determined by 3–21G and 6–31G∗ calculations on the optimized structures. The INDO/S-CIS semiempirical method was applied to predict the excited state energies, the transition dipole moments and the oscillator strengths for the optical transitions. Laser-induced fluorescence (LIF) excitation spectra were measured for FR and SBF cooled in pulsed supersonic expansions of He in the ranges 283.7–296.7 nm and 289.1–305.6 nm, respectively. In the LIF excitation spectra of FR and SBF, highly resolved vibronic bands were observed having the band origins of 33791 and 33047 cm −1 , respectively. The spectral shift of the 0-0 band of SBF to red by 744 cm −1 may be attributed to the spiroconjugation arising from the interaction of four p π orbitals in the different planes.

Conformation-selective photoionization of covalently-linked diaryl compounds: Excimer-mediated one-color two-photon ionization in seeded beams of 1,3-diphenylpropane

Hole-burning spectroscopy and ionization threshold measurement were combined with fluorescence excitation (FE) and resonant two-photon ionization (R2PI) spectroscopies to probe conformation dependence of photoionization for jet-cooled 1,3-diphenylpropane (DPP). The S1←S0 excitation energy dependence of excimer fluorescence and that of one-color R2PI indicate formation of an intramolecular excimer and an efficient photoionization of the excimer that occur at higher energies. The energy threshold for the enhanced photoionization, which concurs with that for the excimer formation, is considerably lower for the trans–gauche (tg) conformer than for the trans–trans (tt) or the gauche–gauche (gg) conformer. These results demonstrate the occurrence of conformation selective excimer-mediated photoionization in DPP. The important precursor role of the singlet excimer in the photoionization is attributed to the conformational similarity between the intramolecular singlet excimer and the most stable ground-state cati...