John C. Travis

Galvanic detection of optical absorptions in a gas discharge

An electrical signal, resulting from discrete optical absorptions, has been observed for a variety of elements, including several for which such an effect had not been previously reported. In the present case, the effect is observed as a change in the voltage across a gas discharge tube produced by irradiation with a laser tuned to the wavelength of a transition of a species in the discharge. This signal may be used—without optical detection apparatus—for spectroscopic investigations or analytical determinations of materials in the discharge. Signals were obtained for transitions of lithium, sodium, calcium, barium, uranium, neon, and helium, in commercial hollow cathode lamps, and neon and helium in conventional discharge tubes.

Laser-enhanced ionization spectrometry

Fundamental Mechanisms of Laser-Enhanced Ionization: The Production of Ions (O. Axner & H. Rubinsztein-Dunlop). Fundamental Mechanisms of Laser-Enhanced Ionization: Signal Detection (J. Travis & G. Turk). Analytical Performance of Laser-Enhanced Ionization in Flames (G. Turk). Applications of Laser-Enhanced Ionization Spectrometry (R. Green). Non Flame Reservoirs for Laser-Enhanced Ionization Spectrometry (N. Zorov). Ions and Photons: Interplay of Laser-Induced Ionization and Fluorescence Techniques in Different Atomic and Molecular Reservoirs (N. Omenetto & P. Farnsworth). Index.

Absorption spectra of metal oxides using optogalvanic spectroscopy

The absorption spectra of neutral flame species may be detected by measuring current changes induced by photon irradiation at wavelengths corresponding to electronic transitions. This paper presents the first results using this optogalvanic spectroscopy to study molecular absorption. Numerous transitions have been detected for ScO, YO, and LaO in the 360–630 nm wavelength region. The most extensive data have been obtained for LaO, where we observe a total of at least four electronic states and 18 sequences. Five of the sequences have not been seen in previous emission studies.

Laser Resonance Ionization Mass Spectrometry

The analysis of inorganic atomic species is greatly facilitated by the coupling of lasers with mass spectrometers. A tunable dye laser, alone or in combination with a pump laser, ionizes atoms by resonant excitation processes; the ions are then analyzed in the mass spectrometer. The laser—mass spectrometer system promises to overcome traditional limits of sensitivity and selectivity and to have diverse applications in analytical chemistry.

Particulates formed by a stabilized high voltage spark discharge

Abstract Light scattering was used to demonstrate the presence of small (⩽1 μm) particles in the immediate surroundings of a stable spark discharge. Several parameters, including electrode composition and surface condition, which are of importance in emission spectrochemical analysis, were found to be of importance in affecting the scattering signal. Electron micrographs of the heaviest particles revealed two distinct types of particles. Analytical implications are discussed.

Detection of sodium trace contamination in furnace atmospheres at 1000 °C

Free sodium atoms were detected by resonance fluorescence in an open contaminated quartz tube heated to 1000 °C. The quartz tube and furnace were similar to those used in semiconductor device processing. Fluorescence was excited by a cw dye laser tuned to the sodium D1 or D2 transition and directed along the axis of the furnace. Fluorescence from the sodium D2 line emitted in the axial direction was collected by a telescopic system and focused onto a photomultiplier tube. The estimated minimum detectable sodium density in the furnace is 5×105 atoms/cm3. No free sodium was detectable in a processing tube that had not been intentionally contaminated.

The Optogalvanic Effect

Every scientist since Albert Einstein has been taught about the photoelectric effect (1), by which photons more energetic than the binding energy of the outer electrons on the surface of a material are capable of producing ionization. The production of ions by collisional processes in plasmas is a familiar phenomenon as well (2). With the benefits of hindsight, it is therefore reasonable to postulate a hybrid ionization process for free atoms or molecules in a plasma, whereby the outer electron is promoted to the ionization potential by a sequence of collisional and optical excitations (3) utilizing discrete electronic energy states as “stepping stones.” One would expect the presence of photons tuned to a transition to increase the ionization rate in such a system.

Intrinsic Wavelength Standard Absorption Bands in Holmium Oxide Solution for UV/visible Molecular Absorption Spectrophotometry

The transmittance minima of 18 absorption bands of a solution of 40 g/L holmium oxide in 10% (volume fraction) perchloric acid are certified as intrinsic traceable wavelength standards, by means of a multicenter measurement on material from a single source coupled with comparisons of a variety of preparations of the material evaluated on a single instrument. Fit-for-purpose artifact standards for the experimental calibration or validation of wavelength scales of chemical spectrophotometers can be carefully produced by end users themselves or by commercial standards producers. The intrinsic (data) standard confers traceability to the SI unit of length in place of costly transfer artifacts and repetitive calibration procedures. Certified values are provided for instrumental spectral bandwidths of 0.1–3.0 nm in 0.1 nm intervals, and information values are provided to a spectral bandwidth of 10 nm at wider intervals. Expanded uncertainties are typically less than ±0.1 nm for certified band positions.

Analytical applications of resonance ionization mass spectrometry (RIMS)

Abstract A perspective on the role of resonance ionization mass spectrometry (RIMS) in the field of analytical chemistry is presented. RIMS provides new, powerful, and complementary capabilities relative to traditional methods of inorganic mass spectrometry. Much of the initial work in RIMS has been to illustrate these capabilities and define the potential of RIMS in the generalized field of chemical analysis. Three areas of application are reviewed here: (1) noble gas measurements; (2) materials analysis using isotope dilution (IDMS); and, (3) solids analysis using direct sampling. The role of RIMS is discussed relative to the more traditional mass spectrometric methods of analysis in these areas. The applications are meant to illustrate the present state-of-the-art as well as point to the future state-of-the-art of RIMS in chemical analysis.

UV/visible Fourier transform spectroscopy using an inductively-coupled plasma : dual-channel noise cancellation

Abstract Although technological advances have extended the range of Fourier transform spectroscopy (FTS) into the UV/visible spectral domain, its application to spectroscopic and spectrometric problems has been hampered-relative to such applications in the infrared domain-by noise considerations. Although the technique retains high resolution, accurate wavelength registration, and simultaneous broad band coverage, the multiplex advantage present in the IR is severely compromised in the UV/visible due to the relative insignificance of detector noise. In particular, signal-carried noise distributes widely through the spectrum, degrading the dynamic range needed for many spectroscopic and analytical applications. This study demonstrates the use of complementary optical output channels in a commercial FTS to achieve up to ten-fold noise reductions for spectra acquired from an analytical inductively-coupled plasma with conventional pneumatic sample aspiration. The study also demonstrates the advisability of increasing the sampling rate of future instruments to exceed the maximum noise frequency characteristic of droplet evaporation effects.