光化学反应中氩气对激发态锂原子猝灭速率研究

本文对光化学法分离中氩气对2P激发态锂原子的碰撞猝灭速率进行研究.在弱激光作用下,通过对不同氩气压强下的锂原子蒸气吸收光谱和激发态锂原子的荧光发射光谱进行测量,得到氩气对2P激发态锂原子的猝灭速率常数为(12.29±0.92)×10-18m3·s-1.实验结果表明:在光化学锂同位素分离研究中,氩气对锂原子2P激发态的猝灭速率远小于2P激发态锂原子的自发辐射速率,碰撞猝灭效应对分离选择性的影响非常小,可以忽略不计.     

Absorption,fluorescence, and fluorescence excitation spectra of free molecules of indole and its derivatives

We have obtained and analyzed the absorption, fluorescence, and fluorescence excitation spectra of indole vapor, N-acetyl-L-tryptophan vapor, and 3-indole aldehyde vapor. From analysis of the dependence of the fluorescence spectrum of the free indole molecules on the wavelength of the exciting radiation λ_ex, it follows that emission of fluorescence occurs when the molecules undergo a transition from the one electronically excited state ¹L_b. The fluorescence spectra of the studied compounds are insignificantly different, suggesting a major role for the indole chromophore in formation of the compounds. The absorption spectrum of N-acetyl-L-tryptophan, in which the group of atoms is added to the indole ring through a-C-C bond, is similar to the spectrum of indole, while the spectrum of 3-indole aldehyde is significantly different from the indole spectrum due to the effect of the C=O group conjugated with the indole ring. The fluorescence excitation spectra are considerably different from the absorption spectra. This is associated with the strong dependence of the quantum yield for the free molecules on λ_ex. Qualitatively, they are mirror-symmetric to the fluorescence spectra of the stodied compounds. Analysis of the data obtained provides a basis for assuming that in the case of free molecules of indole and its derivatives, the ¹L_a absorption in the extreme long-wavelength region of the spectrum does not overlap ¹L_b absorption. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 218–222, March–April, 2007.     

Redistribution of population among the higher levels of Na atoms in an H2-O2-Ar flame

A substantial fraction of the population of Na-atoms in an H₂-O₂-Ar flame is found to be distributed among the higher levels as a result of two-photon laser excitation, spontaneous emission and collisions with flame gas atoms and molecules. Several population inversions are observed. From the laser-excited level upwards, a partial Boltzmann equilibrium, corresponding to the flame temperature, has been found in some cases. Estimates of weighted average rate-constants for collisional energy transfer from groups of higher levels to the 3P-level are given. Some level-pairs appear to be strongly coupled to each other.     

Optical properties of impurity atoms in pressurized superfluid helium

We report on the optical properties of alkali atoms (Cs and Rb) in the pressurized superfluid helium. We observed excitation and emission spectra at various pressures from the saturated vapor pressure to about 25 atm. The theoretical calculations on the basis of the atomic bubble model have also been worked out. The qualitative agreement between the theoretical and experimental results with respect to the peak shift, the linewidth, and their pressure dependence is achieved in the framework of the spherical atomic bubble model. TheD ₂ excitation spectra with the double peaks are interpreted qualitatively in terms of the Jahn-Teller effect, indicating the existence of the nontotally symmetrical density distribution of the surrounding helium atoms.     

The violet emissions produced by laser excitation of Na vapor in the 570–595 nm region

We have observed atomic Na and molecular Na₂ emissions in the violet region when Na vapor in a heatpipe (～10³—10¹⁶ atoms/cm³) is irradiated with a pulsed dye laser with output wavelength in the 570–597 nm region. The Na atomic emissions probably result from recombination of Na⁺ + e^- and energy-pooling involving highly excited atoms and molecules, while the diffuse violet emission bands are probably produced through collisions among excited Na atoms and Na₂ molecules.     

Generation of coherent ultraviolet radiation in the 330 nm region by multiphoton excitation of sodium vapor

We report the observation of coherent uv emission at 330.2±0.5 nm when sodium vapor in a heatpipe is irradiated with a pulsed visible dye laser with output wavelength in the 570–595 nm region. It is found that intense uv emission can be produced from Na atoms as well as from Na₂ molecules. The excitation functions and their dependence on vapor density and laser power density are presented and the mechanisms for producing the emission are discussed.On leave from the Department of Physics, Fujian Normal University, Fuzhou, Fujian, People's Republic of China     

Two-dimensional imaging of glyoxal (C2H2O2) in acetylene flames using laser-induced fluorescence

2 H₂O₂). Laser-induced fluorescence spectra from glyoxal vapor using the same excitation wavelength of 428 nm showed the same strongest lines as the signal from the flame. Glyoxal was visualized in two different modes; two-dimensional imaging and a spatial-spectral mode where spectra were obtained at different spatial positions in the flame simultaneously. For the premixed laminar rich flame it is shown that glyoxal is produced early in the flame, before the signals for C₂ and CH appear. For the turbulent non-premixed flames it is shown that glyoxal is produced in a layer on the fuel rich side of the flames. Here the fuel is premixed with ambient air. This layer is thin and has a high spatial resolution. The general trend was that the glyoxal signal appeared in regions with a lower temperature compared with the emission from C₂ and CH. The imaging of glyoxal in turbulent acetylene flames is a promising tool for achieving new insight into flame phenomena, as it gives very good structural information on the flame front. Tests so far do not indicate that the detected glyoxal is a result of photo-production. To our knowledge, this is the first detection of glyoxal in flames using laser-induced fluorescence. Received: 19 December 1996/Revised version: 26 May 1997     

Excitation of iron atoms in a plasma of excimer emitters under transverse-discharge pumping

The optical characteristics of a transverse-discharge plasma initiated in He/Xe(Kr)/HCl(CF₂Cl₂) mixtures were studied. The mixtures contained a small amount of iron vapor due to metal cathode erosion. The iron atoms were shown to be excited by the spontaneous emission of KrCl (λ=22 nm) and XeCl (λ=308 nm) molecules in a nanosecond transverse discharge.     

Measurement of radiative gas and particle emissions in biomass flames

Radiation is the dominant mode of heat transfer near the burner of coal and biomass-fired boilers. Predicting and measuring heat transfer is critical to the design and operation of new boiler concepts. The individual contributions of gas and particle phases are dependent on gas and particle concentration, particle size, and gas and particle temperature which vary with location relative to the flame. A method for measuring the contributions of both gas and particle radiation capable of being applied in harsh high temperature and pressure environments has been demonstrated using emission from particles and water vapor using an optical fiber probe transmitting a signal to a Fourier Transform Infrared (FTIR) spectrometer. The method was demonstrated in four environments of varying gas and particle loading using natural gas and pulverized wood flames in a down-fired 130?kW_th cylindrical reactor. The method generates a gas and particle temperature, gas concentrations (H₂O and CO₂), total gas and particle intensities, and gas and particle total effective emissivity from line-of-sight emission measurements. For the conditions measured, downstream of the luminous flame zone, water vapor and CO₂ radiation were the dominant modes of heat transfer (effective emissivity 0.13–0.19) with particles making a minor contribution (effective emissivity 0.01–0.02). Within a lean natural gas flame, soot emission was low (effective emissivity 0.02) compared to gas (0.14) but within a luminous flame of burning wood particles (500?µm mean diameter) the particles (soot and burning wood) produced a higher effective emissivity (0.17) than the gas (0.12). The measurement technique was therefore found to be effective for several types of combustion environments.     

Copper hexadecafluoro phthalocyanine and naphthalocyanine: The role of shake up excitations in the interpretation and electronic distinction of high-resolution X-ray photoelectron spectroscopy measurements

We present the first high-resolution X-ray photoelectron core level spectra of bulk copper hexadecafluoro phthalocyanine (CuFPC) and naphthalocyanine (H₂NPC). The measurements have been performed in UHV onto samples grown in situ. A shake-up satellite assigned to a monopole on-site HOMO–LUMO molecular excitation has been evidenced in the F, C and N core-level spectra measured. In the case of the CuFPC, the shake-up is characteristic of the F atoms, of the four N atoms that are Cu bonded, and of the F- and N-bonded C atoms. The shake-up to main peak relative binding energy has been estimated to be 1.6 eV. In the case of H₂NPC, the outer benzenic C atoms do not show a satellite excitation, which instead is characteristic of the C and N atoms belonging to the inner porphyrin-like central ring of the molecule. The shake-up is less than 1 eV at higher binding energies from the main core line. The localisation of the HOMO level in the central structure of the molecule is confirmed by Hartree–Fock all-electron molecular orbital calculations performed on the metal-free phthalocyanine (H₂PC) and hexadecafluoro phthalocyanine (H₂FPC) molecules.     

Laser spectroscopy and optical pumping of alkali atoms in superfluid helium

In this paper, our recent works on the alkali atoms in superfluid helim (HeII) are reported. At first we mentions the laser-sputtering method for implantation, which is simple but is very efficient to produce various kinds of neutral atoms and molecules in HeII. Secondly, we report on the laser spectroscopy of alkali atoms in HeII. Optical excitation and emission spectra are found to be roughly explained by a spherical atomic bubble model, but the spectra corresponding to the D₂ lines indicate the quadrupole oscillation of the bubble shape. Optical pumping by a circularly polarized laser beam is found to produce perfect polarization, for both electron and nuclear spins. Using the rf-optical double resonance techniques, the magnetic and hyperfine resonances are observed. It is discussed also about the phenomena which have observed in the experiments done so far but have not been fully explained.     

Jet flow of vapors in an electric arc and its uses in spectral analysis (a survey)

The effect of the migratory motion of atoms on line intensity in dc arc spectra is considered. Increase in the jet character of vapor flow are accompanied by increases in the fraction of atoms entering the excitation zone. Sensitivity of spectral analysis can be increased by providing for jet flow of iodine vapor through the discharge gap. The use of a carrier (Ga₂O₃) also makes it possible to augment the jet character of the flow at lower vapor flow velocities.     

Photoelectron spectra of F3SiC2H4Si(CH3)3 molecule using monochromatized synchrotron radiation

A variety of photoelectron spectra for gas phase F₃SiC₂H₄Si(CH₃)₃ molecule have been measured using monochromatized undulator radiation and a hemispherical electrostatic analyzer. Valence photoelectron spectrum shows many peaks for ionization from shallow and deep molecular orbitals in the binding energy region of 9–40 eV. A calculation of ionization energies using the outer valence Green's function method indicates energies in agreement with experimental results below 17.5 eV. Spectra for Si L-shell electron emission show chemical shifts of Si atoms induced from different chemical environments around two Si atoms and also exhibit spin–orbit splitting for 2p photoelectrons. Further photoelectron spectra for C K-shell and F K-shell are discussed in comparison with those of related molecules.     

Synthesis and Spectral Characterization of Methyl‐2‐pyridyl Ketone Benzoyl Hydrazone and Its Complexes with Rare Earth Nitrates

Abstract

The hydrazone ligand, methyl‐2‐pyridyl ketone benzoyl hydrazone (L), and its complexes with rare earth nitrates have been synthesized. These new complexes with the general formula of Ln(L)₂(NO₃)₃ · nH₂O (where Ln=La, n=5.5; Ce, Pr, n=5; Nd, Eu, n=4) were characterized by mass spectra, elemental analysis, IR spectra, thermal analysis, UV spectra, molar conductivity, and luminescent spectra. All the complexes are stable in air. The results show that the lanthanide ions in each complex are coordinated through oxygen and nitrogen atoms of the ligand, the oxygen atoms of the nitrate, and coordinated water molecules. The amide‐oxygen atoms of L coordinate to the Ln ions in its keto‐form. Tentative structures for the complexes have been proposed.     

Emission characteristics of a barrier discharge in an Ar-H2O mixture

We have experimentally studied the UV radiation of a low-temperature barrier discharge plasma in an Ar-H₂O mixture. The spectral interval 300–400 nm has been examined in detail. Addition of argon with a pressure of 24 kPa to a barrier discharge in water vapor at a pressure of ～0.1 kPa leads to a ninefold increase in the UV radiation power of excited hydroxyl molecules. An increase in the duration of the UV radiation pulse of the mixture in the longitudinal discharge decay has been achieved for the first time, which may be direct evidence of energy transfer from metastable argon atoms to water molecules. An estimate of the upper boundary of the dissociative excitation rate constant of hydroxyl molecules OH*(A ²Σ⁺) upon interaction of metastable argon atoms with water molecules has been obtained.     

Radiative transfer model of a pyrotechnic flame

A two-line radiative transfer model for predicting the spectral radiant flux of pyrotechnic illuminating flares over a wide range of system variables such as formula, size, and ambient pressure, has been formulated and validated.To solve the transfer equation for observed radiant intensity, the flame is represented by a model whose main characteristics are (a) the flame is a homogeneous gaseous atmosphere with plane-parallel stratification, (b) the gas consists of inert molecules plus sodium atoms which can be excited to the ²P_{$\text{1}\text{2}$} or ²P_{$\text{3}\text{2}$} level, (c) there is local thermodynamic equilibrium governed by the local temperature, (d) the temperature gradient can be represented by a parabola whose vertex is at the center of the flame, (e) the dispersion profile and number density of sodium atoms have average values, inside the flame, that are independent of depth, and (f) the individual line dispersion profile is replaced with a two-line function to simultaneously describe the spectral distribution of both of the sodium D lines.The parameters of the radiative transfer theory were supplied from calculated thermodynamic properties of the flare. Optical thickness as a function of position in the flame was determined using computed sodium atom densities and physical flame size obtained photographically. A flame temperature gradient was constructed numerically as a function of temperature in the flame using the computed temperature at the flame center and the boundary. The two-line dispersion profile was constructed as a function of line broadening. The shape and intensity of the broadened flare spectrum was computed without introducing further assumptions.     

Analysis of the production and clusterization of iron atoms under pulsed laser photolysis of Fe(CO)5

Atomic-resonance absorption spectroscopy is used to study the production and loss of iron atoms under dissociation of the Fe(CO)₅ vapor in a quartz reactor that is induced by the pulses of the KrF excimer laser. Iron atoms populate the ground state owing to the quenching of the excited states generated in the course of the laser photolysis and are detected using the resonance absorption at a wavelength of 385.99 nm. The effective quenching rates are in good agreement with the known rates of the quenching of metastable iron atoms by the Fe(CO)₅ molecules. It is demonstrated that a loss of iron atoms is related to the recombination with dimer and trimer formation and the secondary atomic reactions with the Fe(CO)₅, CO, and FeCO molecules. The rates of the main elementary reactions responsible for the loss of iron atoms are determined using the comparison of the experimental results and kinetic simulation data.     

Detection and Quantitation Of Several Atomic Species By Intra-cavity Quenching Of Laser Emission

Until recently laser research has been the province of the physicist wherein lasers have been utilized extensively as sources of coherent, highly monochromatic energy. The thrust of this research has been to employ the organic solution laser output as an analytical signal from which information about a particular system may be extracted. Preliminary investigations in this laboratory showed that a great number of variables are active in the achievement of lasing from an organic solution. More significantly, concurrent work in this laboratory produced some anomalous results which were subsequently attributed to a cavity defect. This suggested that small energy losses at discrete wavelengths within the resonant cavity of an organic solution laser could result in quenching of broad band laser emission at those specific wavelengths. These considerations led to investigations in which atoms and mlecules were purposefully introduced into the resonant cavity of an organic solution laser.¹ A search of the literature revealed that investigators at The National Bureau of Standards had previously observed this phenomenon and had reported on the intra-cavity absorption of a pulsed rhodamine 6G laser emission by sodium vapor.² In a follow-up paper Keller and co-workers demonstrated the enhancement of absorption for Eu(NO₃)₃) when placed within the cavity of a rhodamine 6G laser. Concurrently absorption was observed from Ba and Sr in an air-acetylene flame within a dye laser cavity by, Thrash et al.⁴ Hansch and co-workers⁵ duplicated the intra-cavity absorption experiment with iodine vapor and compared the sensitivity of this result with measurements obtained from conventional absorption techniques. At about the same time Latz, Wyles, and Green¹ reported data which dennnstrated that the extent of intra-cavity absorption for nitrogen dioxide was linearly related to its concentration. Investigation into the use of a laminar flow burner with an air-acetylene flame within a dye laser cavity showed part per billion (ppb) detection limits for sodium as well as the detection of barium and mercury. The completion of these intracavity absorption studies in the visible region of the spectrum yielded the results which are reported here as well as quantitative intyacavity absorption data for Eu⁺³. In an independent study Konjevic also reported detection of sodium by intra-cavity absorption from an airnatural gas flame⁶.     

Relaxation Processes at High Levels of Vibrational Excitation of Polyatomic Molecules in the Ground Electronic State

By the spectral and kinetic characteristics of the luminescence of vapors of polyatomic molecules (anthracene, anthraquinone, fluorenone) initiated by selective IR multiphoton excitation (IR MPE) of molecules in the ground electronic state S ₀ the relaxation processes proceeding under vibrational excitation of molecules to energies exceeding the energies of the lower excited electronic states have been investigated. The changes in the spectral and kinetic characteristics with increasing CO₂ laser energy density and vapor P _v and foreign gas pressure P _FG are analyzed. They are similar to the characteristics obtained for normal fluorescence of these molecules with changing vibrational energy E _vib content. On the basis of experimental data and model calculations it has been concluded that at the laser radiation densities used in the case of IR MPE the molecules reach energies considerably exceeding the energies of the electronic levels. It is shown that a nonadiabatic connection between the electronic states leads to the population of mixed electronic states isoenergetic to the vibrational levels of the ground electronic state and to emission of delayed luminescence spectrally identical to the normal luminescence of these molecules. It has been found that when high vibrational levels are populated, new relaxation channels, such as reverse electron relaxation, emission from high vibrational levels of the ground electronic state, and multiquantum vibrational energy transfer at collisions leading to a rapid establishment of vibrational equilibrium become important.     

Kinetics of radiation cooling of fullerenes

Emission from fullerene molecules excited by means of electron impact in crossed beams under conditions of single collisions between electrons and C₆₀ molecules in a kinetic energy range E _e from 25 to 100 eV was studied experimentally. Emission spectra in a wavelength range from 300 to 800 nm; the emission excitation functions and the temperature of emitting molecules as a function of E _e were measured with a resolution of 1.6–3.2 nm. The contribution to emission from ionized C ₆₀ ^+* molecules has been determined and data on the emissivity of the C ₆₀ ^+* ion have been obtained. It has been shown that the emission spectra can be well approximated with the spectral distribution of thermal emission from a black body (Planck’s formula), taking into account the lowering of emissivity for a small particle. The emission can be observed starting with electron energy of about 27 eV; the emission excitation function is of a nonresonant form, peaking at an energy of E _e ≈70 eV. As E _e is increased, the temperature of emitting particles rises and reaches its maximum value of 3100–3200 K at E _e ≈47 eV.