Two-dimensional quenching lifetime measurement of OH:A 2 Σ +(υ′ = 1) and NO:A 2 Σ(υ′ = 0) in atmospheric-pressure flames

Planar laser-induced fluorescence is currently widely applied to research on combustion. However, conventional approaches for semi-quantitative measurement could not provide the satisfactory solution and the problem due to collisional quenching remains to be solved. This paper describes the two-dimensional (2D) quenching-time-constant measurement of OH:A ^{2 +}( = 1) and NO:A ² ( = 0) in flame cross sections at atmospheric pressure. These measurements involve 1–2 ns decay time of the excited state using a high-speed image intensifier and a tunable laser with a pulse duration of 3 ns at FWHM. The correlation factors of the exponential fits for the fluorescence decays after the laser pulse were larger than 0.999 in all experiments presented in this study. Furthermore, the measured Stern-Volmer plots of the quenching rate at 1.0, 1/2, 1/3, and 1/4 atm pressure using the same experimental apparatus was confirmed to have a linear relationship for both OH and NO, showing that the 2D decay-time measurements of 1–2 ns have been successful. For NO:A ² ( = 0), the obtained quenching rates inside the inner cone and in the outer flame in the NO-seeded methane-air Bunsen flame were 8.7 × 10⁸ and 7.8 × 10⁸ s^–1, respectively, and for OH:A ² ( = 1), the obtained quenching rate mapping in the outer flame was around 5.6 × 10⁸ s^–1 in the methane-air flame.     

Four-wave mixing in CO via the C 1Σ+ (υ′=0) state

Coherent vacuum ultraviolet (VUV) radiation was generated by four-wave difference frequency mixing (_VUV=2₁–₂) of pulsed dye laser radiation in carbon monoxide (CO). The frequency ₁ was tuned to the C ¹⁺(=0)X ¹⁺(=0) two-photon transition, while the dye laser frequency ₂ was scaned around 17650 cm^–1 which corresponds to the A ¹(=7)«C ¹⁺(=0) transition energy. The VUV intensity was found to be strongly wavelength dependent. The analysis of the spectrum revealed (i) that the VUV intensity was enhanced by the rotational levels of the A ¹(=7) state and (ii) that the off-resonance excitation in the C ¹⁺(=0)X ¹⁺(=0) two-photon transition greatly contributed to the present four-wave mixing process. The effects of pumping laser detuning, saturation and foreign gases are briefly discussed.     

Light Σ hypernuclei and Σ− atoms

The structures of ⁴ He and ⁷ Li are investigated within the frame of the [³H + ⁺] + + [³He + ^o] model and the microscopic cluster model +2N+, respectively. The different binding mechanism between ⁴ He and ⁷ Li is emphasized together with a brief discussion on the ⁴ Be hypernucleus. It is clarified that the ⁴ He hypernucleus is bound due to the cooperative contribution from the and terms of -N interaction, while the ⁷ Li hypernucleus is bound mainly due to the term of -N interaction. The combined analysis of ^– atoms and ⁴ He hypernucleus is shown to be useful to reveal the characteristic differences among the model D, model F and soft core versions of the Nijmegen OBE potentials.The authors would like to express their sincere thanks to J. ofka, O. Richter, M. Sotona, L. Majling, A. Cieply and other colleagues in Nuclear Physics Institute (e/Prague), and H. Band, Y. Yamamoto and T. Motoba, for collaboration and useful discussions. We dedicate this article to the memory of the excellent activities of the late Prof. Jan ofka.     

Measurement of the reaction γp → K0Σat photon energies up to 2.6 GeV⋆

The reaction p K⁰⁺ was measured in the photon energy range from threshold up to 2.6 GeV with the SAPHIR detector at the electron stretcher facility, ELSA, in Bonn. Results are presented on the reaction cross-section and the polarization of the ⁺ as a function of the kaon production angle in the centre-of-mass system, cos^c.m._K, and the photon energy. The cross-section is lower and varies less with photon energy and kaon production angle than that of p K⁺⁰. The ⁺ is polarized predominantly at cos^c.m._K 0. The data presented here are more precise than previous ones obtained with SAPHIR and extend the photon energy range to higher values. They are compared to isobar model calculations.     

The C1 Σ +-B1-Σ + amplified spontaneous emission in CO

The first observation of the amplified spontaneous emission (ASE) from the RydbergC ^{1 +}( = 0) state of CO is reported. When theC ^{1 +}( = 0) state was populated through the two-photon excitation, infrared radiation near 2.0 m was ejected in forward as well as backward directions along the laser propagation. The assignment as theC ^{1 +}( = 0) B ^{1 +}( = 0) transition was confirmed. Several characteristics of ASE from theC ^{1 +}( = 0) state are presented.This work was supported by the Morino Foundation, a Grant-in-Aid (No. 07640697) and that on Priority-Area-Research Photoreaction Dynamics (No. 07228268) from the Ministry of Education, Science, Sports and Culture, Japan.     

Investigation of enhanced HgBr(B 2Σ+−X 2Σ+) laser emission due to collisions of Xe ions and HgBr2

Electronic excitation of Hg and the HgBr radical has been observed during collisions of HgBr₂ with Xe⁺ ions at different laboratory kinetic energies. Emission cross-sections of the most intense band of the HgBr(B ²⁺, v=0–X ²⁺, v=22) transition at 502 nm have been measured at different energies of the projectile ions.     

State-to-state rotational energy transfer in OH (A 2Σ+, υ′=1)

State-to-state rotational energy transfer (RET) coefficients for thermal collisions of OH (A ²⁺, =1) with He, Ar, N₂, CO₂, and H₂O at 300K were determined from time-resolved laser-induced fluorescence (LIF) measurements. The RET coefficients are very similar in both qualitative behaviour and absolute magnitude to those measured previously for OH (A ²⁺, =0).     

Some weak processes in electron-proton collisions

Polarization effects are investigated for processes of single production of strange particles in electron-proton collisions e^±+p ⁺+e^±. Special attention is paid to effects associated with possible application for investigation of similar processes of polarized electron beams and polarized nucleon targets. We point out the important role of the study of polarization effects for determination of the matrix element of processes of the type e^±+p ⁺+e^±.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 78–82, September, 1990.     

Time-resolved LIF of OH in the flame front of premixed and diffusion flames at atmospheric pressure

Time-resolved fluorescence measurements are reported for the OH radical in the flame fronts of laminar atmospheric pressure flames. Effective (collision-limited) lifetimes were determined following excitation of theA ²⁺, = 0 state of OH using a picosecond dye-laser system based on the distributed-feedback principle. Measurements were made in a premixed knife-edge burner for rich CH₄/N₂O/N₂ and CH₄/air flames and in a counterflow diffusion burner for a CH₄/air flame. In the accessible range, results indicate a net dependence of lifetime on temperature intermediate betweenT andT ^0.5 for these flames.     

Chemically produced XeF (B→X) emission

Strong UV emission has been observed in the reactions of XeF₂+SiH₄+F₂ and XeF₂+B₂H₆+F₂. The emission spectra have been identified with the B ²X ² transition of XeF. Possible mechanisms of XeF(B) production are discussed.     

Degenerate four-wave-mixing spectroscopy in NaH

We performed DFWM spectroscopy on X ^–1+–A ¹⁺ transitions in NaH produced in an indirect photochemical reaction between Na(3p) and H₂ and detected v=1, 2 and 3 ground state vibrational levels of NaH molecules, whereas with resonance enhanced CARS, we observed v=0 levels only. This different sensitivity can be explained by considering the Franck-Condon-factors and the relevant damping coefficients for the corresponding transitions in the NaH molecule. Time resolved DFWM spectroscopy showed that NaH(v=1) molecules effectively live much longer than Na(3p) atoms which merely follow the laser excitation pulse.     

Observation of structural units at symmetric [001] tilt boundaries in SrTiO3

Incoherent Z-contrast imaging in the scanning transmission electron microscope allows atom column positions to be deduced directly from the experimental image, including locations where the column separation is less than the resolution limit. Maximum entropy analysis applied to the incoherent image locates the high-Z columns to an accuracy of ±0.2 Å. Oxygen coordination at the boundary plane can be deduced by high spatial resolution electron energy loss spectroscopy, and approximate column positions determined by simple bond-valence sum calculations. Observations of 25° (=85), 36° (=5) and 67° (=13) [001] symmetric tilt grain boundaries in SrTiO₃ bicrystals show that half columns are a ubiquitous feature of grain boundary structural units. The observed structural units can be combined to produce structural models for symmetric tilt boundaries over a 0–90° range. The =17 (410), =5 (310), and =5 (210) are found to be favored boundaries and the structures of all the other tilt boundaries are comprised of these units combined with =1 (100) and =1 (110) structural units. All the proposed boundary models show continuity of grain boundary structure over the entire misorientation range. The =17 (410) structural unit is asymmetric which induces microfacetting on all boundaries less than the =5, 36.87° misorientation.Work Supported by the U.S. Department of Energy under contract DE-Ac05-84OR21400.     

Effect of spin-orbit coupling on the intensity of magnetic dipole transitions in molecular oxygen

The intensities of the¹ _g ⁺ -³ _g ^– and¹_g–³ _g ^– transitions in molecular oxygen are calculated. The radiative lifetimes calculated for the singlet states are 11.4 sec and 67 min for the¹ _g ⁺ and¹_g states, respectively. The experimental values (12 sec and 42 min) obtained from measurements of the integrated absorption intensities of oxygen in the upper atmosphere agree well with calculation. The relationship between a calculation of the intensities and a calculation of the spin Hamiltonian parameters for the³ _g ^s- state is considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 115–120, September, 1978.     

Faceting of Σ3 and Σ9 Grain Boundaries in Copper

Faceting is a well documented phenomenon known both for surfaces and interfaces, particularly, grain boundaries (GBs). Faceting can be considered as a phase transition when the original surface or GB dissociates onto flat segments whose energy is less than that of the original surface or GB. For the investigation of GB faceting a cylindrical Cu bicrystal with an island grain was grown by the Bridgman technique. Grain 1 in this bicrystal is completely surrounded by grain 2. The dissociation 9 3 + 3 proceeds during the growth of the bicrystal. The twins appear instead of {111}₁/{115}₂ or (110)_9CSL facet. GB faceting was studied at 1293 K, 1073 K, and 873 K. The profiles of the GB thermal groove were analysed by atomic force microscopy. Wulff-Herring plots and GB phase diagrams have been constructed for the 3, 9 and 9 + 3 GBs. With increasing temperature the facets with low-density CSL-planes disappear in the GB shape. GB roughening phase transition can be responsible for this phenomenon.     

Simultaneous detection of atomic and molecular hydrogen using a tunable ArF excimer laser

We report preliminary experiments which demonstrate the simultaneous detection of both atomic and molecular hydrogen using a single tunable ArF laser. The tunable ArF laser was modified to lase simultaneously at two wavelengths by the addition of a second grating to the oscillator stage as in earlier work by Ketterle et al. for KrF operation. To our knowledge, this is the first demonstration of dual-wavelength capability with a tunable ArF excimer. The H atom diagnostic utilized tunable ArF excimer laser output at 193.29 nm which was Raman shifted in D₂ (first Stokes) to generate 205.14 nm radiation which then excited the H atom to its (3s, 3d) states via a two-photon transition. Fluorescence was detected at 656 nm on the (3s, 3d) 2p transition. The second wavelength from the tunable excimer was used to excite several rovibronic LIF transitions of hydrogen molecule via two-photon absorption on the E ¹ _g ⁺ X ¹ _g ⁺ (2,0) band. Fluorescence occurs at 750 nm and 830 nm on the (E ¹ _g ⁺ B ¹ _g ⁺ ) transitions.     

Gas‐Kinetic Temperature of Planar High‐Frequency Capacitive Discharge Plasma in N2/CO2/He Gas Mixtures

Using methods of emission spectroscopy, we have determined the gaskinetic temperature fields of planar highfrequency capacitive discharge plasma in N₂/CO₂/He gas mixtures depending on the excitation frequency, discharge current, pressure, and chemical composition of the mixture. It is shown that the dominant contribution to the neutral component heating in the center of the discharge chamber is made by the processes of V–T relaxation of vibrationally excited molecules N₂(X ¹, V) and CO₂(X ¹, V), whereas in the zones near the electrodes an important role in the heating is played, along with the V–T relaxation of the N₂(X ¹, V) and CO₂(X ¹, V) molecules, by the processes of deactivation of the metastable states A ³ of the N₂ molecule.     

Calibration of OH laser-induced fluorescence temperature measurements using thermally dissociated H2O

A method for the calibration of OH temperature measurements using laser-induced fluorescence is demonstrated. The technique depends on the thermal dissociation of water vapor in a furnace. The calibration was demonstrated for the excitation of theA ^{2 +}( = 3) – ² ( = 0) band with a tunable KrF laser. Consistent discrepancies of 3% between calculated and measured temperatures with a standard deviation of 8 % were observed.     

Search forN ϕ (1960) baryon

In the experiments at the SPHINX facility in the 70 GeV proton beam of the IHEP accelerator the diffractive production reactionsp+N[(1385)⁰ K ⁺] +N andp+N[(1385)⁰ K ⁺]+N+ (neutral particles) were studied. In the effective mass spectra of the [(1385)⁰ K ⁺] system in these processes there were no signals from the anomalously narrow baryon stateN (1960) which had been observed earlier in the measurement at the BIS-2 setup.SPHINX Collaboration (IHEP-ITEP)     

A solution spectrum of the nonlinear Schrödinger equation. II

It was shown in a previous communication that the nonlinear Schrödinger equation exhibits a spectrum of eigenfunctions of the form = _k,A _k (coshkx) ^–k and = _k B _k (coshkx) ^–k–1sinhkx, and the corresponding eigenvalues of the energy are related to a band structure with a characteristic energy gap as a significant feature. In the present paper, it is shown that a further spectrum exists exhibiting the general structure = _k=0 A _k(cosh kx)^–k–1/2and = _k=0 B_k(cosh kx)^–k–3/2sinhkx and yielding also a band structure. An extension of the solution spectrum to a nonlinear Klein-Gordon equation and a nonlinear Dirac equation does not imply essential difficulties, and the corresponding characteristic band structure has to be related to a mass spectrum.     

Strong Interactions in Strange Exotic Atoms

Strong interaction level shifts and widths in ^- and K^- atoms have been analyzed. The phenomenological density dependent approach as well as the relativistic mean field (RMF) model yield nucleus optical potentials with a repulsive real part in the nuclear interior. This has important consequences for the spectroscopy of hypernuclei. The study of K^- atoms cannot resolve the depth of the K^- nucleus potential. The fits to the kaonic atom data are satisfactory for both the relatively shallow potentials derived from chiral models and for the deep potentials based on the phenomenological and RMF analyses.