Atomic Resonance Lines Research Articles

The Oscillator Strength in Atomic Absorption Spectroscopy

The role of the oscillator strength in atomic absorption spectroscopy, and in particular in absolute elemental analysis by atomic absorption, is discussed. A universal method for determining atomic lifetimes, and hence absolute oscillator strengths of atomic resonance lines, for almost any element in the Periodic Table is described. It is shown that for the idealized conditions of a pure natural-broadened absorption line and a monochromatic emission line, the peak atomic absorption coefficient is independent of the oscillator strength and that the oscillator strength enters into an atomic absorption signal only through extraneous broadening processes such as Doppler, collisional, and transit-time broadening. An atomic absorption experiment, based on samples of near-stationary laser-cooled atoms and a near-monochromatic diode-laser light source, that satisfies the requirements for “oscillator-strength-free” atomic absorption is described.

Analytical performance of high-voltage neon plasma in glow discharge optical emission spectrometry

In a high-voltage Ne glow discharge plasma (Ne-GDP), calibration factors as well as the limit of determination were compared between atomic resonance lines and singly-ionized lines of copper and aluminium in optical emission spectrometry. These elements have intense ionic lines which are excited by resonance charge-transfer collisions of Ne ions. The ionic lines gave better detection sensitivity in the Ne-GDP, whereas the atomic resonance lines were commonly employed as analytical lines in the other plasma sources such as Ar-GDP and ICP. The limit of determination was 1.3 × 10–3 mass % for the Cu II 248.58 nm line and 1.0 × 10–3 mass % Al for the Al II 358.66 nm line at a discharge parameter of 1.60 kV/36 mA.

Criterion for determining the analytical emission lines in glow discharge optical emission spectrometry.

Two major factors for selecting analytical lines, the sensitivity and the self-absorption effect, were compared between atomic lines and singly-ionized lines of copper as well as vanadium in glow discharge optical emission spectrometry. They have intense ionic lines which are excited through resonance charge-transfer collisions. It was found that the ionic lines are more sensitive compared to the atomic resonance lines; in addition, the ionic lines are essentially free from self-absorption, while the atomic lines suffer from self-absorption to a certain extent. The Cu II 224.70 nm, V II 309.31 nm, and V II 266.32 nm lines in the argon plasma, and the Cu II 270.32 nm line in the neon plasma are recommended as analytical lines of these elements.

Vuv photolysis of hydrazoic acid: Absorption and fluorescence excitation spectra

The vuv-absorption of the HN3/DN3 isotopomers and the formation of NH/ND photofragments in the (c 1Π) and (A 3Π) states were studied. Tunable synchrotron radiation and several atomic resonance lines were used as light sources. The absorption spectrum, which shows more features than reported earlier, was analyzed by means of extensive quantum chemical ab initio calculations. The internal energies of the observed NH/ND(c,A) photofragments were estimated as a function of the photolysis wavelength by emission spectroscopy. The fragment NH/ND(c) is formed with a rather constant quantum yield below 147 nm, while the relative production yield of NH/ND(A) increases with decreasing wavelength. Although NH/ND(A) can be formed directly via a spin forbidden process at long wavelengths, it is more efficiently produced by reactions of the three different triplet N2(A,B,B′) states with HN3/DN3. The variation of the vibrational distribution of the NH/ND(A) radicals indicates that various production mechanisms exist.

Structure and properties of naphthalene containing polyesters, 1. High resolution solid state13C NMR study of poly(ethylene naphthalene-2,6-dicarboxylate)

Poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) crystallizes in two different modifications depending on the temperature of crystallization. The high resolution solid state 13 C NMR spectra of the α modification, β modification and amorphous PEN have been measured by employing cross polarization with magic angle spinning and high power proton decoupling. By application of both a short contact time pulse sequence and an interrupted decoupling pulse sequence all resonance lines, some of which are overlapped in the original 13 C CP/MAS NMR spectra of both amorphous and β modification PEN, are separated. The α modification PEN, β modification PEN, amorphous PEN and PEN in solution show different chemical shifts for each individual carbon atom. The chemical shift difference between amorphous PEN and PEN in solution is much smaller than the difference between either modification crystalline PEN and PEN in solution. The resonance lines of the naphthalene carbon atoms of crystalline PEN have been found to be at a lower field shift than the corresponding lines of PEN in solution. Conversely, the resonance lines of the other carbon atoms on crystalline PEN are shifted upfield from the ones of PEN in solution. A significant difference between the spectra of α and β form PEN can be observed in resonances of the protonated naphthalene carbon atoms C 1 , C 5 , C 4 , and C 8 . They differ by 1.10 ppm. These chemical shift differences are explained in terms of different conformation and chain packing in the samples.

Photodissociation spectroscopy of the Ca+–N2 complex

The weakly bound complex Ca+–N2 is prepared in a pulsed nozzle/laser vaporization cluster source and studied with mass-selected photodissociation spectroscopy. The chromophore giving rise to the electronic transition is the 2P←2S atomic transition of Ca+. The appearance of spin–orbit doublets in the vibrationally resolved spectrum, as expected for a 2∏r←2∑+ transition, confirms that the complex is linear. The electronic transition in the complex lies to the red of the atomic resonance line indicating that the complex is more strongly bound in the excited state than in the ground state. The vibrationally resolved spectrum contains progressions in the Ca+–N2 stretching mode and in a combination of this stretch with the N–N stretch. Extrapolation of the Ca+–N2 stretch determines the excited state dissociation energy to be D0′=6500±500 cm−1, and an energetic cycle determines the ground state value to be D0″=1755±500 cm−1 (5.02 kcal/mol). The 2∏r(2,0,0)←2∑+(0,0,0) vibronic transition has been rotationally resolved yielding the bond lengths: rCaN=2.75 Å and rNN=1.15 Å for the 2∑+ ground state; rCaN=2.48 Å and rNN=1.17 Å for the 2∏ excited state.

Spectroscopy of metal ion complexes: gas-phase models for solvation.

Weakly bound metal ion complexes are produced in molecular beams and studied with mass-selected laser photodissociation spectroscopy. The metal ions Mg+ and Ca+ are the focus of these studies because they have a single valence electron and strong atomic resonance lines in convenient wavelength regions. Weakly bound complexes of these ions with rare-gas atoms and small molecules are prepared with laser vaporization in a pulsed nozzle cluster source. The vibrationally and rotationally resolved electronic spectra obtained for these complexes help to determine the complexes' structures and bonding energetics. Observations from these studies have provided many new insights into the fundamental interactions in electrostatic bonding.

Selection of self-absorption free analytical lines of aluminum in glow discharge optical emission spectrometry

To obtain a larger dynamic range in the glow discharge emission spectrometric determination of aluminum, the use of the ionic lines instead of the atomic resonance line was suggested. The ionic lines are essentially free from self-absorption leading to better linearity of analytical curves, while the atomic lines suffer from self-absorption to a certain extent. The ionic lines of aluminum are hardly emitted by the argon plasma; however, they can be excited by the neon-argon as well as the argon-helium mixed gas plasma. Therefore, the mixed plasma gases should be used. Calibration curves were measured for the different plasma gases and the concentration interval over which they were linear was estimated.

Fluorescence excitation spectroscopy of Xenon doped Neon clusters: size and site effects, and cluster melting

Electronic excitations of Xe atoms and Xe2 molecules embedded in free Ne clusters are studied with time resolved fluorescence excitation spectroscopy. Several distinct absorption bands blueshifted relativ to the first atomic resonance line of Xe are observed and are attributed to Xe or Xe2 located in different sites. For Ne clusters containing less than 300 atoms only interior sites are observed indicating that small Ne clusters are liquid-like.

NMR studies of buspirone (an anxiolytic drug) analogues

Conformations of piperazine rings in 8-{4-[4-(2-pyrimidyl)-1-piperazinyl]butyl}-8-azaspiro[4.5]-decane-7,9-dione (buspir-one — 1) and its two analogues 8-{4-[4-(2-quinolinyl)-1-piperazinyl]butyl}-8-azaspiro[4.5]-decane-7,9-dione (kaspar — 2) and 4,4-dimethyl-1-{4-[4-(2-quinolinyl)-1-piperazinyl]butyl}-2,6-piperidinedione (mesmar — 3) (Fig. 1) have been studied with the aid of 1H NMR and 13C NMR spectra. For free bases the two bands corresponding to piperazine hydrogen atoms in the spectra broaden considerably with a decrease in temperature to divide into four separate bands, indicating the presence of a dynamic exchange process. A similar dynamic process, but for higher temperatures, was observed for buspirone ( 1), kaspar ( 2) and mesmar ( 3) hydrochlorides. Proton and carbon atom resonance lines have been assigned with the aid of 2D COSY and 2D HETCOR two-dimensional spectra.

Branching Ratios of Excited Sn I States Produced by Collisions of He(23S) Atom with SnCl4 and Sn(CH3)4

Abstract Fluorescence in the 200—600 nm range from excited fragments produced by collision of He(23S) with SnCl4 and Sn(CH3)4 has been studied in the relative collision energy of 135—210 meV. Emission cross sections for Sn I atomic resonance lines from SnCl4 slightly decrease with increasing collision energy. This originates from the fact that the effective potential between He(23S) and SnCl4 is slightly attractive. The branching ratio of Sn I states observed from SnCl4 is consistent with a simple dissociation model assuming equipartition of the available energy. These results are compatible with the harpoon mechanism as an initial step for formation of Sn I from SnCl4. On the other hand, the effective potential between He(23S) and Sn(CH3)4 is found to be repulsive, and the branching ratio of Sn I is increased to much more than that estimated from the statistical model. Excited Sn I states seem to be produced directly from Sn(CH3)4 by an excitation transfer mechanism via superexcited states, which mainly decay by Penning ionization.

Atomic Data for Permitted Resonance Lines of Atoms and Ions from H to Si, and S, Ar, Ca, and Fe

We list vacuum wavelengths, energy levels, statistical weights, transition probabilities, and oscillator strengths for permitted resonance spectral lines of all ions of 18 astrophysically important elements (H through Si, S, Ar, Ca, Fe). Using a compilation of experimental energy levels, we derived accurate wavelengths for 5599 lines of 1828 ground-term multiplets which have gf-values calculated in the Opacity Project. We recalculated the Opacity Project multiplet gf-values to oscillator strengths and transition probabilities of individual lines. For completeness, we added 372 resonance lines of Ne I, Ar I, Fe I, and Fe II ions which are not covered by the Opacity Project. Intercombination and forbidden lines are not included in the present compilation.

Photodissociation spectroscopy of Ca+–rare gas complexes

Weakly bound complexes of the form Ca+–RG (RG=Ar, Kr, Xe) are prepared in a pulsed nozzle/laser vaporization cluster source and studied with mass-selected resonance enhanced photodissociation spectroscopy. The Ca+ (2P←2S) atomic resonance line is the chromophore giving rise to the molecular spectra in these complexes. Vibrationally resolved spectra are measured for these complexes in the corresponding 2Π←X 2Σ+ molecular electronic transition. These spectra are red shifted from the atomic resonance line, indicating that each complex is more strongly bound in its excited 2Π state than it is in the ground state. Vibronic progressions allow determination of the excited state vibrational constants: Ca+–Ar, ωe′=165 cm−1; Ca+–Kr, ωe′=149 cm−1; Ca+–Xe, ωe′=142 cm−1. Extrapolation of the excited state vibrational progressions, and combination with the known atomic asymptotes and spectral shifts, leads to determination of the ground state dissociation energies Ca+–Ar, D0″=700±100 cm−1 (0.09 eV); Ca+–Kr, D0″=1400±150 cm−1 (0.17 eV); Ca+–Xe, D0″=2300±150 cm−1 (0.29 eV). The spin–orbit splitting in the 2Π1/2,3/2 state for these complexes is larger than expected by comparison to the Ca+ atomic value.

Photodissociation spectroscopy of MgCH+4

The photodissociation spectroscopy of MgCH+4 has been studied in a reflectron time-of-flight mass spectrometer. MgCH+4 molecular absorption bands are observed to the red of the Mg+(3 2PJ←3 2S1/2) atomic ion resonance lines. The photofragmentation action spectrum consists of a broad structureless continuum ranging from 310 nm to 342 nm, and peaking near 325 nm. In this spectral region, both the nonreactive (Mg+), and two reactive fragmentation products (MgH+ and MgCH+3) are observed, all with similar action spectra. The product branching is independent of wavelength, Mg+:MgCH+3:MgH+∼60:33:7. The absorption is assigned to the transition (1 2E←1 2A1) in C3v symmetry (with η3 coordination), followed by a geometrical relaxation of the complex toward states of 2B1 and 2B2 symmetry in C2v geometry (with η2 coordination). Dissociation requires a nonadiabatic transition to the ground electronic surface. Analysis of broadening in the photofragment flight time profile shows the nonreactive Mg+ product angular distribution to be isotropic, with an average translational energy release which increases slightly from Et∼370±150 cm−1 at 332.5 nm to Et∼520±180 cm−1 at 315 nm. These values are less than 2% of the available energy and are well below statistical expectations. Analogous experiments on MgCD+4 show the kinetic energy release in the nonreactive channel to be significantly larger for the CD4 case, ranging from Et∼540±180 cm−1 at 332.5 nm to Et∼830±200 cm−1. These results clearly demonstrate that the dissociation is nonstatistical. Preliminary ab initio potential surface calculations suggest a possible dynamical mechanism to explain these unusual results.

Pressure shift of atomic resonance lines in liquid and solid helium

We show that for atoms trapped in a liquid He matrix the excitation and emission spectra can be quantitatively described by the bubble model which treats the matrix as an incompressible continuous medium. Comparison with experimental results shows that the model also holds for a solid matrix. The model is only valid in the case where the attractive He−He interaction dominates the attractive part of the foreign atom-helium interaction. Its failure in the case of implanted Na atoms is discussed.

Spectroscopic study of rare-gas excimer formation in a direct-current discharge with supersonic expansion

Emission spectra of the rare-gas excimers Ar2*, Kr2*, and Xe2* were excited in a dc jet discharge with supersonic expansion. Absorption and fluorescence emission measurements provided atomic population densities for levels of the 1s manifold. Changes in intensities of the atomic resonance lines and the VUV bands were examined as the plasma was irradiated with laser radiation tuned to specific atomic transitions between levels of the 1s and 2p manifolds. This technique of optical pumping has established that excimers in the A 3Σ+u state are the main contributors to the observed bands from this source. Rate equations were developed to explain the observed intensity changes. Comparisons of the calculated and observed changes indicated that population mixing amongst levels of the 1s manifold caused by electron collisions is an important process in regulating the population in the 1s5 atomic level that leads to the formation of rare-gas excimers by collisions with ground level atoms.

Optical tomography of plasmas by spectral interferometry

A white light illuminated Mach-Zehnder interferometer and a spectrograph are used to obtain spectral side-on interferograms of a steady state free burning arc for different observation directions by rotating the arc between taking the records. The vertical plasma column contains chromium atoms being evaporated by plasma-wall interactions from an electrically insulated and cascaded cylindrical chromium oxide wall surrounding the discharge in the bottom electrode region. The phase change of light waves passing the plasma column is determined highly resolved in the spectral neighbourhood of resonance lines of neutral chromium atoms using FFT algorithms. The angularly dependent integral phase changes corresponding to different observation directions are subject to a computerized tomographic reconstruction procedure yielding the spatially resolved distribution of ground state chromium atoms in the observed cross section of the slightly asymmetric plasma column.

Pressure shift and broadening of the resonance line of barium atoms in liquid helium.

We have measured the pressure broadening and shift of the excitation and emission lines of the 6${\mathit{s}}^{2}$ $^{1}$${\mathit{S}}_{0}$\ensuremath{\rightarrow}6s6p $^{1}$${\mathit{P}}_{1}$ transition of Ba atoms implanted in liquid and solid helium at 1.5 K. The observed spectra are quantitatively explained within the adiabatic line-broadening theory by assuming a bubble structure of the trapping sites for the Ba atoms. The evolution of the bubble shape and size in the optical excitation-deexcitation cycle is modeled theoretically.

Photodissociation spectroscopy of Mg+–rare gas complexes

Weakly bound complexes of the form Mg+–RG (RG=Ar, Kr, Xe) are prepared in a pulsed nozzle/laser vaporization cluster source and studied with mass-selected photodissociation spectroscopy. The chromophore giving rise to the molecular spectra in these complexes is the 2P←2S Mg+ atomic resonance line. A 2Σ+ ground state and 2Σ+ and 2Π excited states are derived from this atomic transition. Vibrationally resolved spectra are measured for each of these complexes in the A 2Π←X 2Σ+ electronic transition. These systems are redshifted from the atomic resonance line, indicating that each complex is more strongly bound in its excited 2Π state than it is in the ground state. Extended vibrational progressions allow determination of the respective vibrational constants: Mg+–Ar, ωe′ = 272 cm−1; Mg+–Kr, ωe′ = 258 cm−1; Mg+–Xe, ωe′ = 258 cm−1. Extrapolation of the excited state vibrational progressions, and combination with the known atomic asymptotes and spectral shifts, leads to determination of the respective dissociation energies: Mg+–Ar, D0″= 1281 cm−1 (3.66 kcal/mol; 0.159 eV); Mg+–Kr, D0″ = 1923 cm−1 (5.50 kcal/mol; 0.238 eV); Mg+–Xe, D0″ = 4182 cm−1 (11.96 kcal/mol; 0.519 eV). The spin–orbit splitting in the 2Π1/2,3/2 state for all complexes is larger than expected by comparison to the Mg+ atomic value. This larger splitting in the complexes, which is attributed to configuration mixing with states on the rare gas atoms, increases for the series Ar, Kr, Xe, and decreases linearly for higher vibrational states of each complex.

Assessment of the population of neutral and singly ionized zinc species in argon and argon—nitrogen inductively coupled plasma by atomic absorption spectrometry

Atomic absorption measurements were used to determine the relative number densities of both zinc atoms and ions in an inductively coupled plasma (ICP). Variations in the absorbance obtained with the zinc atomic and ionic resonance lines reflect the dynamic equilibrium between the number of atoms and ions in the plasma. Absorbance changes as a function of the carrier gas flow-rate were investigated at several incident power values. Ionization is drastically reduced at higher carrier gas flow-rates. Measurements at different observation heights were carried out with widely differing flow-rates of the carrier gas. The results obtained for the tail plume zone are different from those for other zones of the ICP. The characteristics of the ICP using argon-nitrogen mixed gas instead of argon alone were also examined by atomic absorption spectrometry.