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We observed the fluorescence excitation spectra and dispersed fluorescence spectra of jet-cooled coronene-h

Fluorescence excitation spectra and fluorescence lifetimes at single vibronic levels in the S 1 state have been observed for jet-cooled pyrene. The fluorescence lifetimes at the zero-vibrational levels of the S 1 1 B 3 u states of pyrene- h 10 and pyrene- d 10 are 1480 and 1470 ns, respectively, and the relaxation is considered to be dominated by the radiative process. For some vibrational levels, however, the lifetimes are remarkably shorter such as 765 ns at the 221 vibronic level of pyrene- h 10 ( ν 22 ( b 1 g ); C–H bending and skeletal deforming mode), indicating that nonradiative transition occurs at a specific vibrational level. In this study, we demonstrate that the main process is internal conversion to the S 0 1 A g state caused by nonadiabatic vibronic interaction via b 3 u promoting modes.

We observed fluorescence excitation spectra and dispersed fluorescence spectra for single vibronic level excitation of jet-cooled perylene-h 12 and perylene-d 12, and carefully examined the vibrational structures of the S0[1] A g and S1[1] B 2u states. We performed vibronic assignments on the basis of the results of ab initio calculation, and found that the vibrational energies in the S1 state are very similar to those in the S0 state, indicating that the potential energy curves are not changed much upon electronic excitation. We conclude that the small structural change is the main cause of its slow radiationless transition and high fluorescence quantum yield at the zero-vibrational level in the S1 state. It has been already reported that the lifetime of perylene is remarkably short at specific vibrational levels in the S1 state. Here, we show that the mode-selective nonradiative process is internal conversion (IC) to the S0 state, and the ν16(a g ) in-plane ring deforming vibration is the promoting (doorway) mode in the S1 state which enhances vibronic coupling with the high-vibrational level (b 2u ) of the S0 state.

We observed the fluorescence excitation spectra and mass-selected resonance enhanced multiphoton ionization (REMPI) excitation spectra for the 6(0)(1), 6(0)(1)1(0)(1), and 6(0)(1)1(0)(2) bands of the S1←S0 transition of jet-cooled deuterated benzene and assigned the vibronic bands of C6D6 and C6HD5. The 6(0)(1)1(0)(n) (n = 0, 1, 2) and 0(0)(0) transition energies were found to be dependent only on the number of D atoms (ND), which was reflected by the zero-point energy of each H/D isotopomer. In some isotopomers some bands, such as those of out-of-plane vibrations mixed with 6(1)1(n), make the spectra complex. These included the 6(1)10(2)1(n) level or combination bands with ν12 which are allowed because of reduced molecular symmetry. From the lifetime measurements of each vibronic band, some enhancement of the nonradiative intramolecular vibrational redistribution (IVR) process was observed. It was also found that the threshold excess energy of "channel three" was higher than the 6(1)1(2) levels, which were similar for all the H/D isotopomers. We suggest that the channel three nonradiative process could be caused mainly by in-plane processes such as IVR and internal conversion at the high vibrational levels in the S1 state of benzene, although the out-of-plane vibrations might contribute to some degree.

Fluorescence excitation spectra of dibenzofuran in a supersonic jet are observed and the vibronic structure is analyzed for the S(1) (1)A(1) (pipi) and S(0) states. An observation of the rotational envelopes reveals that the band is a B-type band. However, it is shown that most of the strong vibronic bands are A-type bands. The intensity arises from vibronic coupling with the S(2) (1)B(2) state. We find a broad emission in the dispersed fluorescence spectrum for the excitation of the high vibrational levels in the S(1) state. This indicates that intramolecular vibrational redistribution (IVR) occurs efficiently in the isolated dibenzofuran molecule.

The two-color fluorescence depletion process of Rhodamine 6G in PMMA matrixes was investigated using nano- and picosecond lasers. Erase-lasers of 1064 and 599 nm depleted the fluorescence from the S1 state. Fluorescence depletion with 1064 nm was analyzed by the up-conversion from state S1 to S2, while that with 599 nm was simulated based on both the up-conversion and the stimulated emission. A three-state model describes this process due to a nanosecond laser well, while it could not reproduce that by picosecond lasers. Significant contributions of vibrational relaxation in S1 and re-absorption from S0 are suggested in the picosecond region.

We have constructed a picosecond time-resolved IR dip spectrometer having a frequency resolution of 60 μJ). The picosecond time-resolved IR dip spectra of phenol–(H2O)1 and carbazole–(H2O)1 are presented to demonstrate the capability of the constructed system. The spectral changes show clear vibrational structures of not only S0, but also S1 in the 2800–3800 cm−1 energy region. The system performance is also discussed.

Picosecond time-resolved IR spectra of phenol–(NH3)3 have been measured by UV–IR–UV ion dip spectroscopy for the first time. It was found that the time-evolution of two vibrational bands at 3180 and 3250 cm −1 is different from each other. The results show that two transient species are generated from the photo-excited phenol–(NH3)3 cluster. From ab initio calculation, the transient species are assigned to two isomers of (NH3)2NH4.

We investigated the S1 and S2 states of linear and zigzag cata-condensed hydrocarbons on the basis of the results of jet spectroscopy and theoretical calculations. The S1 states of anthracene and tetracene are represented by the HOMO → LUMO configuration (Φ(A)), whereas those of phenanthrene and chrysene are represented by HOMO-1 → LUMO and HOMO → LUMO+1 configurations (Φ(B)). We found that the fluorescence lifetime varied with different vibronic levels in the S1 states of linear cata-condensed hydrocarbons due to the mode-selective internal conversion to the S0 state. This selectivity is likely to be seen in the S1 Φ(A) state of the D(2h) molecule.

Sumanene is a typical buckybowl molecule with C3v symmetry. We observed a fluorescence excitation spectrum and a dispersed fluorescence spectrum of sumanene in a supersonic jet. Bowl effects were clarified by comparing the spectra with those of triphenylene (D3h symmetry), which is a planar prototype of nonplanar sumanene. The S1 (1)A1 ← S0 (1)A1 transition is symmetry allowed. We found the 0(0)(0) band in the fluorescence excitation spectrum at 357.78 nm; this band was missing in the forbidden S1 (1)A1(') ← S0 (1)A1(') transition of triphenylene. The transition moment was shown to be along the oblate symmetric top axis (out of plane) by the observed rotational contour. A large number of vibronic bands were observed, unlike in triphenylene. Some were considered to be out-of-plane vibrational modes, which lead to a bowl-to-bowl inversion reaction assisted by in-plane vibrations. We found that the vibronic bands were markedly weak in the high energy region of triphenylene-d12. This indicates that the fluorescence quantum yield is very low at the high vibrational levels in the S1 state due to the rapid radiationless transition. The main process is considered to be internal conversion to the S0 state. The nonplanar structural distortion may also enhance radiationless transitions. We could not, however, observe weakening of the vibronic bands in the fluorescence excitation spectrum of sumanene.

Rotaviruses were detected via electron microscopy in fecal specimens collected from school children during an outbreak of diarrhea and from a sporadic case in 1993 in Japan. All of the viruses were found to belong to human group C rotavirus by reverse passive hemagglutination assay (RPHA). These viruses replicated well in a human colon carcinoma (CaCo-2) cell line cultured in the presence of trypsin (4 micrograms/ml). This report demonstrates that human group C rotaviruses can be propagated efficiently in a cell line cultured in the presence of trypsin. The infected cells did not show any apparent cytopathic changes. However, virus was detected in the cell cytoplasm by immunofluorescence (IF) staining and in the culture supernatant by RPHA. On the basis of immune electron microscopy (IEM), virus particles collected from infected CaCo-2 cell cultures were confirmed to aggregate specifically with anti-human group C rotavirus antibody. The electrophoretic patterns of RNA segments extracted from viral particles found in the fecal specimens or infected cells were identical to those of human group C rotavirus. These results indicated that human group C rotaviruses were the causal agent of the diarrhea outbreak.

We observed the fluorescence excitation spectra and dispersed fluorescence spectra of jet-cooled coronene-h12 and coronene-d12. We analyzed the vibronic structures, assuming a planar and sixfold symmetric molecular structure (D6h). The S1 state was identified to be B2u1. The S1B2u1←S0A1g1 transition is symmetry forbidden, so the 000 band is missing in the fluorescence excitation spectrum. We found a number of vibronic bands that were assigned to the e2g fundamental bands and their combination bands with totally symmetric a1g vibrations. This spectral feature is similar to that of benzene although several strong e2g bands are seen in coronene. The band shape (rotational envelope) was significantly different in each e2g mode. It was shown that degenerate rotational levels were shifted and split by the Coriolis interaction. We calculated the Coriolis parameter using the molecular structure in the S1 state and the normal coordinate of each e2g vibrational mode, which were obtained by theoretical calculations....

Electronic and vibrational structures in the S(0) (1)A(1) and S(1) (1)A(1) states of jet-cooled phenanthrene-h(10) and phenanthrene-d(10) were analyzed by high-resolution spectroscopy using a tunable nanosecond pulsed laser. The normal vibrational energies and molecular structures were estimated by ab initio calculations with geometry optimization in order to carry out a normal-mode analysis of observed vibronic bands. The rotational structure was analyzed by ultrahigh-resolution spectroscopy using a continuous-wave single-mode laser. It has been demonstrated that the stable geometrical structure is markedly changed upon the S(1) ← S(0) electronic excitation. Nonradiative internal conversion in the S(1) state is expected to be enhanced by this structural change. The observed fluorescence lifetime has been found to be much shorter than the calculated radiative lifetime, indicating that the fluorescence quantum yield is low. The lifetime of phenanthrene-d(10) is longer than that of phenanthrene-h(10) (normal deuterium effect). This fact is in contrast with anthracene, which is a structural isomer of phenanthrene. The lifetime at the S(1) zero-vibrational level of anthracene-d(10) is much shorter than that of anthracene-h(10) (inverse deuterium effect). In phenanthrene, the lifetime becomes monotonically shorter as the vibrational energy increases for both isotopical molecules without marked vibrational dependence. The vibrational structure of the S(0) state is considered to be homogeneous and quasi-continuous (statistical limit) in the S(1) energy region.

The excitation energy migration of rhodamine B doped in amorphous silica glasses prepared by the sol-gel method has been studied with a picosecond time-resolved fluorescence spectrophotometer. The excitation energy relaxation was interpreted in terms of energy migration among energetically disordered monomer sites and energy trapping by trap sites in the glass.

A study on the possibility of diarrhea induced by EPA and autoxidized EPA (EPA-Ox ; 61.6% decomposition) was conducted using several assays on rabbits and suckling mice. The result of loop test of both EPA and EPA-Ox in rabbit intestine showed positive diarrheal effect at the dose of more than 12.5 mg per loop though the degree of effect depended on the rabbit used (no sign was observed in 2 out of 6 rabbits). Effect of EPA-Ox was more intense than EPA. In an oral test with suckling mice, however, neither of the acids showed a diarrheal effect at a dose of up to 5 mg/mouse. When a very small amount (1.0μg) of okadaic acid (OA) was given, positive toxicity identified as a typical diarrheal substance derived from phytoplanktons. Significant positive correlation (γ=0.984, p

Vibrational level structure in the S(0) (1)A(g) and S(1) (1)B(3u) states of pyrene was investigated through analysis of fluorescence excitation spectra and dispersed fluorescence spectra for single vibronic level excitation in a supersonic jet and through referring to the results of ab initio theoretical calculation. The vibrational energies are very similar in the both states. We found broad spectral feature in the dispersed fluorescence spectrum for single vibronic level excitation with an excess energy of 730 cm(-1). This indicates that intramolecular vibrational redistribution efficiently occurs at small amounts of excess energy in the S(1) (1)B(3u) state of pyrene. We have also observed a rotationally resolved ultrahigh-resolution spectrum of the 0(0) (0) band. Rotational constants have been determined and it has been shown that the pyrene molecule is planar in both the S(0) and S(1) states, and that its geometrical structure does not change significantly upon electronic excitation. Broadening of rotational lines with the magnetic field by the Zeeman splitting of M(J) levels was very small, indicating that intersystem crossing to the triplet state is minimal. The long fluorescence lifetime indicates that internal conversion to the S(0) state is also slow. We conclude that the similarity of pyrene's molecular structure and potential energy curve in its S(0) and S(1) states is the main cause of the slow radiationless transitions.

Rotationally resolved high-resolution spectra and fluorescence decay curves have been observed for weak and short-lived vibronic bands of the S(1) (1)B(3u)-- S(0) (1)A(g) transition of naphthalene. Fluorescence lifetime of the vibronic band with an excess energy of 1390 cm(-1) (0(0)(0) + 1390 cm(-1) band) is remarkably shorter than that of other bands. Zeeman splitting of rotational lines is very small, so that the main radiationless process is not intersystem crossing to the triplet state but internal conversion to the ground state. The lifetime is thought to be governed by the strength of vibronic coupling between vibrational levels of the S(0) and S(1) states. As for the 0(0)(0) + 2570 cm(-1) band, energy shifts were found in only a few rotational levels although the excess energy was higher than the threshold of intramolecular vibrational redistribution. We conclude that all of the rotational levels are mixed with other vibrational levels. The 0(0)(0) + 3068 cm(-1) band spectrum is fairly complicated with numerous rotational lines, which is attributed to strong vibronic coupling with the S(2) (1)B(2u) state.

Fluorescence excitation spectra and dispersed fluorescence spectra of jet-cooled 9-methylanthracene-h12 and -d12 (9MA-h12 and 9MA-d12) have been observed, and the energy levels of methyl internal rotation (CH3 torsion) in the S0 and S1 states have been analyzed. The molecular symmetry of 9MA is the same as that of toluene (G12). Because of two-fold symmetry in the pi system, the potential curve has six-fold barriers to CH3 rotation. In toluene, the barrier height to CH3 rotation V6 is very small, nearly free rotation. As for 9MA-h12, we could fit the level energies by potential curves with the barrier heights of V6(S0) = 118 cm(-1) and V6(S1) = 33 cm(-1). These barrier heights are remarkably larger than those of toluene and are attributed to hyperconjugation between the pi orbitals and methyl group. The dispersed fluorescence spectrum showed broad emission for the excitation of 0(0)(0) + 386 cm(-1) band, indicating that intramolecular vibrational redistribution efficiently occurs, even in the vibronic level of low excess energy of the isolated 9MA molecule.

Excimer formation of pyrene and naphthalene doped amorphous silica glasses prepared by the sol-gel method has been studied with a picosecond time-resolved fluorescence spectrophotometer. In high dopant concentration of pyrene and naphthalene, the picosecond time-resolved fluorescence spectra show two kinds of excimer emissions originating from a sandwich-type and second excimer in pyrene doped amorphous silica glass and one excimer emission from second excimer in naphthalene doped amorphous silica glass.

From the measurement of fluorescence spectra in pyrene and naphthalene doped amorphous silica glasses with high dopant concentration prepared by the sol-gel method, the broad emission by the molecular aggregation in these glasses was observed at a longer wavelenght than the monomer band. The fluorescence decay curves of the monomer emission are interpreted in terms of the energy migration among organic molecules which are dispersed in the amorphous silica glass and energy trapping by the organic molecules aggregated in the glasses.

Steady-excitation fluorescence spectra of pyrene-doped amorphous silica glasses prepared by the sol—gel method were measured. A broad excimer-like emission was observed in higher dopant concentrations. The picosecond time-resolved fluorescence spectra and the fluorescence excitation spectra suggest that a ground-state dimer is responsible for the broad excimer-like emission.

We present a nanosecond pump-and-probe optical study of wurtzite GaN under the excitation condition that the carrier-longitudinal optical phonon scattering does not contribute to the energy relaxation process. The delay time after which the isothermal condition is achieved is found to be ∼50 ns. This comes from both the phonon structure in GaN and the fact that the carrier cooling depends on excess kinetic energies of carriers.

The HeLa cell line which is one of the most popular cell lines was shown to be suitable for isolation of types A (H3N2) and B influenza viruses from throat washings of patients. Sixty-nine and 67 out of 147 throat washings taken from patients during the period from January to April 1994, were positive for influenza A virus in HeLa cells and MDCK cells respectively. Seven out of 10 throat washings taken between January and March, 1993, were positive for influenza B virus in MDCK. Of these 7, 4 were also positive for HeLa cells.

Fluorescence and absorption spectra of rhodamine dyes doped in amorphous silica glasses prepared by the sol-gel method were studied. With increasing acidity of hydrolysis, the peaks of both spectra show a blue-shift for rhodamine B and a red-shift for rhodamine 6G. These results are related with the molecular forms of rhodamine dyes.

In this paper, THz-radiation power from semiconductors irradiated with a femtosecond-optical pulse is significantly enhanced and reaches up to 110 /spl mu/W under 1.7 T magnetic field; we also found a dramatic change of ellipticity. A mode-locked Ti:sapphire laser delivered 100-fsec pulses at 760 nm for the excitation.

Recently developed tunable solid-state UV laser material Ce/sup 3+/:LiLuF/sub 4/ (Ce:LLF) with tunability of about 305-340 nm is attractive for a variety of applications including environmental remote sensing and combustion diagnostics.

We have demonstrated a new, simple, and intense terahertz-radiation source just using bulk InAs. An average power of 650 /spl mu/W was achieved in a 1.7-T magnetic field with 1.5-W excitation power. A dramatic change of ellipticity was also observed for different magnetic fields.

We have demonstrated a new scheme for generating intense far-infrared or THz radiation pulses synchronously with near-infrared pulses using a saturable Bragg reflector placed inside a mode-locked laser cavity. With this newly proposed simple scheme, THz radiation which peaked at around 0.66 THz, with an average power of 2–3 nW is directly generated synchronously with femtosecond near-infrared optical pulses.

Time-resolved fluorescence spectra have been investigated on anthracene crystals in the range of 4–12 eV by the time-correlated single-photon counting technique using pulsed radiation from a synchrotron source. The time-resolved excitation spectra of the singlet excitation fluorescence are significantly dependent on time and exciting photon energy. In a subnanosecond time period during the pulse excitation, the fluorescence detected near the absorption edge has a high quantum efficiency when the exciton bands are resonantly excited by the polarized light along the b -axis. Meanwhile, for the off-resonance excitations, the fluorescence rises with a time delay of about 1 ns and obeys a purely single-exponential decay. Possible interpretations of the time correlation between the flourescence and the excitation spectra observed in the subnanosecond time period are made on the basis of the excitonic polariton model.

A total of 13 strains of Mycoplasma were isolated from 15 strains of established cell lines. All of them, except an unidentified strains were of human origin, including 5 strains of M. orale and 7 strains of M. hominis.Each of three cell strains, BHK21, RK13 contaminated with M. orale, and HmLu contaminated with M. hominis, was treated with a culture medium containing gentamicin (200γ/ml), kanamycin (250γ/ml), and tylosin (250γ/ml) or containing kanamycin and tylosin (250 or 500γ/ml each) for 9 days by changing the medium every other day.Mycoplasma was eliminated from RK13 cells even with the medium containing 250γ/ml each of kanamycin and tylosin and from HmLu cells only with the medium containing the three antibiotics. None of these cell lines yielded Mycoplasma during the subsequent 21 passages for a period of 150 days in the absence of the antibiotics used to the treatment. Mycolasma could not be eliminated from BHK21 cells, but the combination of the three antibiotics was more effective for treatment of the cells than that of two antibiotics.The results obtained suggest that the combined use of multiple antibiotics may be promising in eliminating Mycoplasma from cell culture, without giving any damage to the cells.

Pyrene-doped amorphous silica glasses were prepared by the sol-gel method. The optical properties of these pyrene-doped amorphous silica glasses, such as the absorption spectra, the excitation spectra, the fluorescence spectra, and the fluorescence decay time, were measured and compared with those in ethanol solution. From the dependence of these optical properties on the pyrene dopant concentration, the degree of molecular dispersion in the amorphous silica glasses is discussed.

For the three azabenzenes pyridine, pyrazine and pyrimidine, quantum yields for fluorescence and intersystem crossing have been measured in the vapour phase as a function of the excitation energy, ranging from the zero-point level of S1(n, π*) to the higher vibrational levels of S2(π, π*). The picosecond fluorescence lifetimes have also been measured by exciting the molecules at various wavelengths. For all three azabenzenes a particularly fast non-radiative decay channel has been found. The appearance of this new decay channel has also been demonstrated by direct measurement of the picosecond lifetime. In the lower excitation-energy region of the S1â†�S0 transition the intersystem-crossing process is dominant, whereas above the excitation-energy threshold the non-radiative transition is governed by this decay channel. These new decay channels in azabenzenes may be related to photoisomerization processes, which are known to proceed by irradiation of u.v. light corresponding to the S2â†�S0 absorption transition. The discussion is developed in relation to “channel three” in the parent hydrocarbon, benzene.