High-resolution Emission Spectroscopy Research Articles

Kinetics of ozone and nitric oxides in dielectric barrier dischargesin O2/NOx and N2/O2/NOx mixtures

Concentrations of NO, NO2, NO3, N2O5, and O3 weremeasured by classical absorption spectroscopy in dielectric barrierdischarges in flowing O2/NOx and N2/O2/NOx mixtures. Theresults of measurements in different parts of the discharge chamber and inits exhaust are compared to a numerical zero-dimensional kinetic model and goodagreement is found. The experimentally found upper limit of the NOxconcentration allowing ozone production is confirmed by the kineticcalculations for both gas mixtures. The rotational temperature of differentnitrogen bands was measured by high-resolution emission spectroscopy. Theresults are explained on the basis of a simplified model and related to thegas temperature in the microdischarge channel and the surrounding gas.

Fourier transform spectroscopy of BaO: New ground-state constants from the A 1Σ+–X 1Σ+ chemiluminescence

The A 1Σ+–X 1Σ+ emission spectrum of BaO excited in a Broida-type oven was revisited using a Fourier transform spectrometer. Chemiluminescence was observed from excited BaO molecules generated from the Ba+N2O reaction, and 82 vibrational bands of 138BaO were measured in the range 8900–21 000 cm−1 at a resolution of 0.04 cm−1. Vibrational levels were observed up to v″=20 of the ground state and up to v′=11 for the excited state. In addition, 72 bands from the minor isotopomers 137BaO, 136BaO, and 135BaO were detected with v″ up to 14 and v′ up to 4. Over 15 500 lines with J″ up to 119 were measured with a precision of about 0.005 cm−1, which shows that the Broida oven is an excellent source for high-resolution emission spectroscopy. Our main goal here is to obtain an optimum set of molecular constants for the ground electronic state. To avoid complications due to the well-known perturbations for vA′⩾1 of the A 1Σ+ state, our unified combined-isotopomer analysis used a novel combination of a Dunham expansion description of the ground state with independent band-constants for data involving A-state level vA′=0, while fitting to an independent term value for each observed A-state vA′⩾1 vibration–rotation level of each isotopomer. Significantly improved ground-state constants and A-state vA′=0 band constants are obtained, together with term values for some 1372 higher-v′ A-state levels.

FTIR Emission Spectra, Molecular Constants, and Potential Curve of Ground State GeO

Extensive new high-temperature, high-resolution FTIR emission spectroscopy measurements for the five common isotopomers of GeO are combined with previous diode laser and microwave measurements in combined isotopomer analyses. New Dunham expansion parameters and an accurate analytical potential energy function are determined for the groundX1Σ+state.

High resolution emission and absorption spectroscopy for erosion product analysis in boundary plasmas

The highly resolved spectra of the silicon multiplet around 251 nm are studied for plasmas in front of a C/C-SiC target interacting with a nearly cylindrically symmetric low temperature plasma jet. The erosion rates from this target are deduced from the silicon density distribution, which is determined from the line intensity ratios and details of the line profiles. Under the conditions of the plasma parameters in this plasma-target interaction experiment these spectral line parameters depend on the optical depths of the emitting and absorbing silicon atoms along the line of sight. The spectral line central branching ratios of lines with quite different products of absorption oscillator strength and statistical weight are most sensitive to the optical depth. In the case of high plasma jet currents the density of the eroded silicon is found to reach values of up to 5×1018 m−3 in agreement with gravimetric measurements.

Experimental Studies of the Structure of Transition Elements

The experimental methods for high resolution emission spectroscopy of line-rich elements are briefly described. A review is given of the general atomic structure of the neutral and singly ionized transition group elements. Details of the structure are compared between elements within a period and homologous elements in different periods. Measurements of hyperfine and isotope structure are dicussed, with examples from recent work.

INVERSE RADIATIVE ANALYSIS OF HIGH-RESOLUTION INFRARED EMISSION DATA FOR TEMPERATURE AND SPECIES PROFILES RECOVERIES IN AXISYMMETRIC SEMI-TRANSPARENT MEDIA

The paper deals with the temperature and species concentration profile recoveries in semi-transparent media by means of inverse radiative methods using high-resolution emission spectroscopy data in order to study the basis of remote metrology of flames. One considers an axisymmetric one-dimensional absorbing–emitting object, the spectral intensities data of which stem from projections obtained by scanning a given cross section in a given line of sight. The inverse method uses a two-line ratio technique whose lines originated from the same lower and upper vibrational states. The study is specialized for carbon monoxide gas traces. The microscopic expressions of the absorption coefficient for the ro-vibrational lines is defined in terms of local species and temperature distributions including line profile with temperature-dependent half-width. The domains of validity of the mathematical assumptions necessary to render the inversion process feasible are discussed. The inversion technique proceeds either by means of a generalized Abel transform or by means of the conjugate-gradient method associated to the integral operator and its adjoint.

Zinc-substituted hemoglobins: alpha- and beta-chain differences monitored by high-resolution emission spectroscopy.

The absorption and emission properties of hybrid Zn-substituted human hemoglobin (Hb) were used to monitor differences in interaction between the porphyrin and the polypeptide chain for the two subunits. Although alpha-substituted (alpha-ZnHb), beta-substituted (beta-ZnHb), or totally substituted Hb all show optical properties characteristic of Zn porphyrins, the spectra are also indicative of specific interactions between the polypeptide chain and the porphyrin. The Q0,0 absorption band of alpha-ZnHb at 5 K shows a splitting of approximately 300 cm-1, comparable to the largest split ever reported for a heme protein. This value is approximately 140 cm-1 for beta-ZnHb. The possible origin of the split is discussed in terms of the local electric field imposed by the amino acids of the respective heme pockets, different configurations of the porphyrin, and/or influences of the liganding histidine. The Zn derivatives show quasiline spectra under fluorescence line narrowing conditions, and the resolved excitation spectrum reveals differences in the vibrational levels of the Zn porphyrin in the two subunits. Broad underlying emission in the fluorescence line-narrowed emission spectrum can be accounted for, in part, by the existence of the two closely spaced electronic origins and also by the extent of phonon coupling between the porphyrin and the protein matrix.

Nanostructure of the rapidly quenched magnetic alloy NdFeB

High-resolution field emission spectroscopy has been used to study the nanostructure of the NdFeB alloy. This revealed a fine banded structure of the grain-boundary phase which is responsible for the high coercivity of the alloy.

High-resolution photoelectron emission spectroscopy of surface states on Ni(111)

One-photon and two-photon photoelectron emission (1PPE/2PPE) spectroscopy is used to study surface states at and below the Fermi energy on Ni(111) in $\overline{\ensuremath{\Gamma}}\ensuremath{\rightarrow}\overline{K}$ and $\overline{\ensuremath{\Gamma}}\ensuremath{\rightarrow}\overline{M}$ direction. Picosecond UV laser pulses at \ensuremath{\lambda}=210.70 nm ($\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\nu}}=47460.16{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$) and \ensuremath{\lambda}=351.17 nm ($\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\nu}}=28476.09{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$) are used for photoexcitation. The energy of the emitted photoelectrons is analyzed in a time-of-flight spectrometer with an energy resolution of $\ensuremath{\Delta}E<20\mathrm{meV}.$ Two surface states located below the Fermi energy and energetically separated by 120 meV are detected at $\overline{\ensuremath{\Gamma}}.$ With increasing ${k}_{\ensuremath{\parallel}}$ the high-energy state disperses upwards, while the low-energy state disperses downwards. Furthermore, a theoretical investigation is performed in the framework of the relativistic one-step formalism. The measured surface-state dispersions are shown to be quantitatively described by the calculations. For the relative and absolute intensities of the two surface states at and around $\overline{\ensuremath{\Gamma}}$ experiment and theory are not in agreement.

A water-stable and strongly luminescent self-assembled non-covalent lanthanide podate †

The segmental ligand 2-(6-carboxypyridin-2-yl)-1,1′-dimethyl-2′-(5-methylpyridin-2-yl)-5,5′-methylenebis(1H-benzimidazole) (L9) reacted with an equimolar mixture of LnIII (Ln = La or Eu) and ZnII in basic conditions to give selectively the self-assembled dinuclear non-covalent podates [LnZn(L9 – H)3]2+. Electrospray mass spectrometry and proton NMR spectroscopy show that [LnZn(L9–H)3]2+ adopt the expected head-to-head triple-helical structure with ZnII pseudo-octahedrally co-ordinated by the bidentate binding units of the three segmental ligands and LnIII occupying the remaining facial pseudo-tricapped trigonal prismatic site produced by the wrapped unsymmetrical tridentate units. Upon UV irradiation, solutions of [EuZn(L9 – H)3]2+ in acetonitrile or in water produce strong red luminescence. The Eu (5D0) lifetime and quantum yield indicate that EuIII is efficiently protected from external interactions for complex concentration in the range 10–4–10–8M and that no solvent molecule enters the first co-ordination sphere. Electrospray mass spectrometry combined with high-resolution emission spectroscopy confirm that the structure of the dinuclear triple-helical complex [EuZn(L9 – H)3]2+ is maintained at low concentration which strongly contrasts with the lipophilic analogous non-covalent lanthanide podates [EuZn(Li)3]5+ {i = 7 or 8; 2-[6-(organo)pyridin-2-yl]-1,1′-dimethyl-2′-(5-methylpyridin-2-yl)-5,5′-methylenebis(1H-benzimidazole)} which are decomplexed in acetonitrile for concentrations below 10–5M. Detailed photophysical studies have established that [EuZn(L9 – H)3]2+ works as an efficient UV → VIS light-converting device in the solid state and in water.

High-Resolution Field Emission Spectroscope.

A new apparatus for high-resolution field emission spectroscopy has been developed by combining the two techniques of extremely high vacuum and high-energy-resolution electron spectroscopy. The base pressure of the constructed vacuum sys tem was 10-10 Pa, and the pressures of 10-9 Pa were maintained in the field emission experient. The high energy resolution of 1 meV was attained with three stages of cylindrical electrostatic analyzers. The typical energy distribution of the field emission from a tungsten (111) tip at room temperature obtained with the apparatus agreed with the theoretical curves based on the Fowler-Nordheim theory.

High-resolution Fourier-transform emission spectroscopy of the A ^4Π-X ^4Σ^- system of WN

The electronic emission spectrum of WN has been observed in the 500–580-nm spectral region with a Fourier-transform spectrometer. The bands were excited in a tungsten hollow-cathode lamp in the presence of a trace of molecular nitrogen. The observed bands have been assigned to the A4Π–X4∑− transition. The ground state is a regular 4∑− state belonging to Hund’s coupling case (a′). The principal ground-state constants obtained from the fit of the observed lines are B0=0.4663779(62),D0=3.5847(77)×10−7,γ0=0.051862(21)cm−1.The excited state, on the other hand, shows Hund’s case (c) tendencies with the spin components mixed because of interactions with other neighboring states. There have been no previous observations of the WN molecule to our knowledge.

High resolution emission spectroscopy of AlCl at 20 μ

The high resolution infrared emission spectrum of aluminum monochloride has been recorded with a Fourier transform spectrometer. A total of 1747 rovibrational transitions, v=1→0 to v=8→7, for the most abundant isotopomer 27Al35Cl and 708, v=1→0 to v=4→3, for the least abundant isotopomer 27Al37Cl have been assigned. This new set of infrared data was combined with existing microwave and millimeter-wave data to refine the Dunham Yij constants for the X 1Σ+ electronic ground state. In addition two sets of mass-reduced Dunham Uij constants have been determined from separate fits. In the first fit all of the Uij constants that could be statistically determined were treated as adjustable parameters. In the second fit only the constants satisfying the condition j<2 were treated as adjustable parameters while the values for the remaining constants were fixed to constraints imposed by the Dunham model. Finally, in order to fully utilize the information provided by this extensive data set in an attempt to improve the prediction of energies for higher lying v, J levels of the X 1Σ+ state, the combined data set, consisting of microwave, millimeter, and infrared (IR) data were fitted directly to the eigenvalues of the Schrödinger equation containing a parametrized internuclear potential energy function.

Laser and Zeeman spectroscopy of Pr 3+ : CsCdBr 3; a simplified crystal field model

Trivalent transition ions associate in pairs when doped in CsCdBr 3 crystals. Using high resolution absorption and emission spectroscopy, we have measured the energy levels of Pr 3+ : CsCdBr 3 and determined their associated irreducible representations. From Zeeman measurements we obtained the g factor for the 1D 2 multiplet ( g ⌈ = 0.9; g ⊥ = 0) and the predictions of a sim crystal field model show that Pr 3+ ions see mainly an octahedral contribution, plus a small C 3v distortion. We also use these measurements to determine a value of the hyperfine interaction constant A J( 1D 2 of 440 +- 150 MHz which is smaller than the value previously determined for Pr 3+ : LaF 3.

Ion beam diagnostics by Doppler shifted light emissionsa)

Broad ion beams in the energy range of 0.2 to 1.5 keV originating from a filament source with argon as feed gas have been analyzed by high-resolution emission spectroscopy. The Doppler structure of Ar+ emissions reveals the existence of different velocity classes. Besides slow ions and ions possessing the main beam energy, electronically excited Ar+ ions with twice the main beam energy are detected which are attributed to a single-electron capture process in Ar++/Ar collisions. As a preliminary result from a reactive beam extracted from a microwave CF4 source plasma fast F atoms are detected which are attributed to charge exchange and dissociative collisions in the process chamber.

High-resolution absorption and emission spectroscopy of high Z laser-produced plasmas (abstract)

Up to 7 kJ of 0.53 μm laser light was used to irradiate solid and thin foil high Z disk targets. The 1 ns flat-topped laser pulses were focused to an intensity greater than 1016 W/cm2. The spectra were recorded on a 3 m grazing incidence spectrograph. We have extended the range of ions observed to emit lines in the O-like, F-like, Na-like, and Cu-like isoelectronic sequences. In addition, layered targets and atomic mixtures have been used to study opacity effects and VUV line emission. This work was performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under contract No. W-7405-ENG-48.

Theoretical predictions and experimental detection of the SiC molecule.

The 0-0 band of the $d^{1}\ensuremath{\Sigma}^{+}\ensuremath{-}b^{1}\ensuremath{\Pi}$ electronic transition of SiC was detected near 6100 ${\mathrm{cm}}^{\ensuremath{-}1}$. The SiC molecule was observed by high-resolution Fourier-transform emission spectroscopy from a composite-wall hollow cathode. Ab initio quantum chemical calculations confirm the identity of the carrier of the spectrum as SiC and the $d^{1}\ensuremath{\Sigma}^{+}\ensuremath{-}b^{1}\ensuremath{\Pi}$ assignment. Combination of the observed ${r}_{0}$ for SiC $b^{1}\ensuremath{\Pi}$ with theoretical shifts in bond lengths from $b^{1}\ensuremath{\Pi}$ to $X^{3}\ensuremath{\Pi}$ gives the astrophysically important bond lengths ${r}_{0}=1.723$ \AA{} and ${r}_{e}=1.719$ \AA{} for $X^{3}\ensuremath{\Pi}$ to an estimated accuracy of 0.001 \AA{}.

High resolution emission spectroscopy (Shpol'skii effect) : A new analytical technique for the analysis of polycyclic aromatic hydrocarbons (PAH) in the environmental samples

High resolution spectrofluorometry (HRS) in n-alkane matrices (Shpol'skii effect) is demonstrated to be an attractive technique for the analysis of several PAH series in environmental samples ( aquatic sediments, aerosols, crude oils,). Analytical results obtained by HRS on crude samples have been also compared with those obtained by other analytical methodologies.

Multivacancy Effects in Atomic and Molecular Spectra

Chemical applications of X-ray spectra are inhibited by the general occurrence of multivacancy processes. These manifest themselves in emission �spectra as extra lines (or satellites) while opening of channels to these initial configurations leads to extra detail in absorption spectra. While there are a few simple cases where this situation has been more or less fully discussed, the more interesting areas are those which are both not simple and not understood. There is, however, a fairly general experimental procedure by which this .complex situation could, in principle, be clarified. This involves carrying out high resolution emission spectroscopy as a function of exciting photon energy in regions containing both single and multiple vacancy thresholds. In earlier work summarised here, it was possible to demonstrate the procedure for a monatomic gas, argon. Subsequently, we have built and now operate a beamline designed specifically for such studies at the National Synchrotron Light Source (NSLS) in Brookhaven. Very recent results from this line and from a few experiments using conventional sources are summarised.

High-resolution emission spectroscopy of CO2 collisionally excited by N2. Rotational distribution

We obtained, for the first time, high-resolution rotational distribution of CO2 collisionally excited by N2. The rotational distribution is non-Boltzmann, and the initial results suggest that surprisingly large impact parameter collisions contribute substantially to the collisional excitation, even though small impact parameter collisions are more effective, as expected.