Russell H. Barnes

Initiation of laser‐supported‐detonation (LSD) waves

Experimental results of plasma diagnostic measurements taken during the early development of laser‐supported‐detonation (LSD) waves in TEA‐CO2 laser irradiations of solid surfaces in air are reported. Photographic and sample examination results for irradiations of practical aluminum surfaces indicate that the initiation process is highly local at surface features which are heated preferentially. The intensity dependence of time to plasma initiation was measured using target‐electron emission, target‐hole transmission, and electrostatic‐probe response as indicators of the initiation event timing. The initiation time for aluminum was found to be in the range 25–70 nsec for peak‐power densities in the range 0.4 to 4×108 W/cm2. Emission‐spectroscopy results indicate the presence of neutral aluminum vapor at late times in the pulse, but no ionized aluminum was detected at atmospheric pressure. The experimental results for aluminum are found to be consistent with a simple theoretical model, wherein electrons ar...

Nitric oxide measurements in a flame by laser fluorescence

Laser fluorescence measurements have been performed to detect nitric oxide in a CH(4)-O(2)-N(2) flame at atmospheric pressure. For these measurements a frequency-doubled tunable dye laser was used to excite the UV gamma-bands of nitric oxide. Sensitivities were adequate to detect naturally occurring levels of nitric oxide that were in the 20-30-ppm range. Higher sensitivities can be achieved using other currently available lasers having greater output intensities.

Two‐step excitation of fluorescence in iodine monochloride vapor

Two‐step sequential excitation of fluorescence was produced in ICl vapor using two synchronized tunable laser sources. The pumping scheme involved the E←A←X electronic transitions with subsequent E→A transitions being observed in fluorescence.

Ultraviolet spectral efficiencies of surface-spark discharges with emphasis on the iodine photodissociation laser pumpband

Spectroscopic studies of the uv emission from surface-discharge sparks across Al(2)O(3), BN, ZnO, ZrO(2), BaTiO(3), ZnO-Al(2)O(3), and Cr(2)O(3).Al(2)O(3) substrates have been performed in He, N(2), CO(2), Ar, SF(6), and Ar + i-C(3)F(7)I gases at pressures of 1-10 atm. Considerable differences were found in the performance of the various substrates; based on absolute measurements which are believed to be conservative, an electrical-to-optical conversion efficiency of 9.4 +/- 1.1% for uv emission in the 2500-2900-A iodine-laser pumpband was obtained from discharges across a Cr(2)O(3).Al(2)O(3) substrate in Ar gas. Pumpband energy densities of several J/cm(2) are readily attainable.

Laser NO(2) fluorescence measurements in flames.

NO(2) fluorescence measurements have been made in a CH(4)/O(2)/N(2) flame at atmospheric pressure using a pulsed tunable dye laser. The results indicate that it should be possible to achieve sub-ppm sensitivities for NO(2) in flames using currently available lasers.

Micro-Diffuse Reflectance and Matrix Isolation Fourier Transform Infrared Techniques for the Identification of Tetrachlorodibenzodioxins

Micro-diffuse reflectance Fourier transform infrared (DRIFT) and matrix isolation (MI) Fourier transform infrared spectra of the 22 tetrachlorodibenzodioxin (TCDD) isomers have been recorded. The DRIFT and MI techniques required about four minutes and one-half minute, respectively, of signal averaging to produce high signal-to-noise (S/N) spectra on low-nanogram-level samples. Spectral subtraction was employed to remove DRIFT solvent impurity interferences. The validity of the DRIFT subtraction technique was demonstrated by comparison of the corrected DRIFT, with the chromatographically pure, MI spectra. The reproducibility of DRIFT frequencies and intensities was tested by comparison of the 1,3,7,8-TCDD spectra from samples independently prepared by two analysts. The MI technique successfully identified 2,3,7,8 in environmental samples. MI spectral subtraction was applied to one sample to remove a coeluting impurity. The DRIFT and MI spectral techniques, used in conjunction with modern chromatographic separation and spectral subtraction, are very promising for the on-line or off-line differentiation of low-level toxic isomeric compounds.

Oxygen Quenching Measurements for the S1 and S2 Fluorescence of Gas-Phase Fluoranthene

The fluorescence emission of the fluoranthene molecule has been investigated at excitation wavelengths varying from 240 to 360 nm, and conducted from near collision-free conditions to atmosphericpressure conditions. The oxygen quenching rate for the fluorescence of the F1 band (S1 → S0 transition) of fluoranthene at 340 nm excitation wavelength was found to be 1 × 109 L mol−1 s−1. The quenching rate for the F2 band (S2 → S0 transition) was found to be 100-fold greater for the wavelength region investigated. The wavelength dependency of the oxygen-quenching constants of the two transitions was also established in the excitation range from 240 to 332 nm. The influence of oxygen and nitrogen pressure on the spectral fluorescence bandwidth of fluoranthene and the oxygen-quenching constants for the S1 and S2 bands are reported. The results shed some light on fluoranthenes unusual inertness to oxygen quenching.

Infrared open-path monitoring for studies of atmospheric dispersion of gaseous pollutants

This paper describes an automated FT-IR open path monitoring system that bas been installed at Tinker Air Force Base to monitor volatile organic hydrocarbon (VOC) emissions from the Industrial Waste Treatment Plant. Coordinated FT-IR and gas sampling measurements were performed to provide a basis for the development of plume dispersion calculations to predict emission source strengths and fenceline concentrations. Methods developed to perform this analysis are described.

Transient Thermal Response of Electrical Conductivity Due to Joule Self‐Heating

Calculations of the time‐dependent conductance of a sample exhibiting an activated conductivity and undergoing Joule self‐heating have been performed for a transient approximation. Measurements of the time‐dependent conductance of the compound NixMn3−xO4 using fast‐rise‐time pulsing are in agreement with the calculated response. A thin‐disk cylindrical geometry was utilized.

Effects of spectral resolution on the identification of specific chemical compounds within complex spectral signatures

This paper presents preliminary results on the effects of spectral resolution and atmospheric transmission on the recovery of species concentrations using Partial Least Squares procedures. The effects of different levels of random spectral noise on the recovery of concentrations are also explored. Calculations were limited to absorbance spectra, however, future effort is to be directed to more realistic passive sensing cases where radiative-transfer effects are taken into account.