Kevin C. Gross

Absolute pKa Determinations for Substituted Phenols

The CBS-QB3 method was used to calculate the gas-phase free energy difference between 20 phenols and their respective anions, and the CPCM continuum solvation method was applied to calculate the free energy differences of solvation for the phenols and their anions. The CPCM solvation calculations were performed on both gas-phase and solvent-phase optimized structures. Absolute pK(a) calculations with solvated phase optimized structures for the CPCM calculations yielded standard deviations and root-mean-square errors of less than 0.4 pK(a) unit. This study is the most accurate absolute determination of the pK(a) values of phenols, and is among the most accurate of any such calculations for any group of compounds. The ability to make accurate predictions of pK(a) values using a coherent, well-defined approach, without external approximations or fitting to experimental data, is of general importance to the chemical community. The solvated phase optimized structures of the anions are absolutely critical to obtain this level of accuracy, and yield a more realistic charge separation between the negatively charged oxygen and the ring system of the phenoxide anions.

Substituent effects on the physical properties and pKa of aniline

The aniline molecule is nonplanar, with its NH2 group lying at an angle of approximately 42 to the plane of the benzene ring. Substituents on the phenyl ring alter this out-of-plane angle as well as other molecular properties such as the ring bond lengths and angles, the barrier to inversion Einv ,a nd the pKa of the amino group. Ab initio 6-311G quantum chemical calculations have been employed to examine these substituent influences and the extent to which they are interrelated. Electron-donating substituents increase the C—N bond length R(C—N),, Einv ,a nd the pKa ,w hereas electron-withdrawing substituents have the opposite effect. Among the molecular parameters that might serve as regression indicators for these changes, Hammett constants, which traditionally have been used to represent substituent electronic effects, yield fair to good correlations for R(C—N) (r 2 D 0.797), (r 2 D 0.804), Einv (r 2 D 0.829), and the amino group pKa (r 2 D 0.931) for aniline and 18 substituted anilines. Of several measures of atomic charge, the Mulliken and electrostatic charges on the amino nitrogen atom show essentially no correlation with these properties. In contrast, the natural charge Qn on the amino nitrogen is well correlated with the bond length R(C—N) (r 2 D 0.889), (r 2 D 0.932), Einv (r 2 D 0.839), and the amino group pKa (r 2 D 0.960). This latter result suggests that the natural charge, rather than either the Mulliken or electrostatic charges, may be the preferred charge descriptor for correlation purposes. Inclusion of electron correlation at the MP2 level increases the correlations of Einv with both (r 2 D 0.951) and Qn (r 2 D 0.892). c 2000 John Wiley & Sons, Inc. Int J Quantum Chem 80: 1107-1115, 2000

Remote Identification and Quantification of Industrial Smokestack Effluents via Imaging Fourier-Transform Spectroscopy

Industrial smokestack plume emissions were remotely measured with a midwave infrared (1800-3000 cm(-1)) imaging Fourier-transform spectrometer operating at moderate spatial (128 × 64 with 19.4 × 19.4 cm(2) per pixel) and high spectral (0.25 cm(-1)) resolution over a 20 min period. Strong emissions from CO(2), H(2)O, SO(2), NO, HCl, and CO were observed. A single-layer plume radiative transfer model was used to estimate temperature T and effluent column densities q(i) for each pixels spectrum immediately above the smokestack exit. Across the stack, temperature was uniform with T = 396.3 ± 1.3 K (mean ± stdev), and each q(i) varied in accordance with the plume path length defined by its cylindrical geometry. Estimated CO(2) and SO(2) volume fractions of 8.6 ± 0.4% and 380 ± 23 ppm(v), respectively, compared favorably with in situ measurements of 9.40 ± 0.03% and 383 ± 2 ppm(v). Total in situ NO(x) concentration (NO + NO(2)) was reported at 120 ± 1 ppm(v). While NO(2) was not spectrally detected, NO was remotely observed with a concentration of 104 ± 7 ppm(v). Concentration estimates for the unmonitored species CO, HCl, and H(2)O were 14.4 ± 0.3 ppm(v), 88 ± 1 ppm(v), and 4.7 ± 0.1%, respectively.

Mid-IR hyperspectral imaging of laminar flames for 2-D scalar values.

This work presents a new emission-based measurement which permits quantification of two-dimensional scalar distributions in laminar flames. A Michelson-based Fourier-transform spectrometer coupled to a mid-infrared camera (1.5 μm to 5.5 μm) obtained 256 × 128pixel hyperspectral flame images at high spectral (δν̃ = 0.75cm(−1)) and spatial (0.52 mm) resolutions. The measurements revealed line and band emission from H2O, CO2, and CO. Measurements were collected from a well-characterized partially-premixed ethylene (C2H4) flame produced on a Hencken burner at equivalence ratios, Φ, of 0.8, 0.9, 1.1, and 1.3. After describing the instrument and novel calibration methodology, analysis of the flames is presented. A single-layer, line-by-line radiative transfer model is used to retrieve path-averaged temperature, H2O, CO2 and CO column densities from emission spectra between 2.3 μm to 5.1 μm. The radiative transfer model uses line intensities from the latest HITEMP and CDSD-4000 spectroscopic databases. For the Φ = 1.1 flame, the spectrally estimated temperature for a single pixel 10 mm above burner center was T = (2318 ± 19)K, and agrees favorably with recently reported laser absorption measurements, T = (2348 ± 115)K, and a NASA CEA equilibrium calculation, T = 2389K. Near the base of the flame, absolute concentrations can be estimated, and H2O, CO2, and CO concentrations of (12.5 ± 1.7) %, (10.1 ± 1.0) %, and (3.8 ± 0.3) %, respectively, compared favorably with the corresponding CEA values of 12.8%, 9.9% and 4.1%. Spectrally-estimated temperatures and concentrations at the other equivalence ratios were in similar agreement with measurements and equilibrium calculations. 2-D temperature and species column density maps underscore the Φ-dependent chemical composition of the flames. The reported uncertainties are 95% confidence intervals and include both statistical fit errors and the propagation of systematic calibration errors using a Monte Carlo approach. Systematic errors could warrant a factor of two increase in reported uncertainties. This work helps to establish IFTS as a valuable combustion diagnostic tool.

Phenomenological fireball model for remote identification of high-explosives

Many aspects of detonation phenomena have been well studied over the last century. However, the transient infrared and visible emissions from detonation fireballs have been poorly understood, and this has hampered attempts to remotely identify explosives via combustion signatures. Recently, time-resolved infrared spectra (1800-7000 cm-1, 4cm-1 resolution, 8 Hz) were collected from the detonation of uncased charges of TNT and several kinds of improvised explosive devices in four weight classes (10, 50, 100, and 1000 kg). A simple model for fireball emissions has been developed which accurately describes the observed spectra in terms of the fireball size, temperature, gaseous byproduct concentrations, and grey particulate absorption coefficient. The model affords high-fidelity dimensionality reduction and provides physical features which can be used to distinguish the uncased explosives.

Imaging Fourier-transform spectrometer measurements of a turbulent nonpremixed jet flame

This work presents recent measurements of a CH4/H2/N2 turbulent nonpremixed jet flame using an imaging Fourier-transform spectrometer (IFTS). Spatially resolved (128×192 pixels, 0.72  mm/pixel) mean radiance spectra were collected between 1800  cm(-1)≤ν˜≤4500  cm(-1) (2.22  μm≤λ≤5.55  μm) at moderate spectral resolution (δν=16  cm(-1), δλ=20  nm) spanning the visible flame. Higher spectral-resolution measurements (δν=0.25  cm(-1), δλ=0.3  nm) were also captured on a smaller window (8×192) at 20, 40, and 60 diameters above the jet exit and reveal the rotational fine structure associated with various vibrational transitions in CH4, CO2, CO, and H2O. These new imaging measurements compare favorably with existing spectra acquired at select flame locations, demonstrating the capability of IFTS for turbulent combustion studies.

Instrument calibration and lineshape modeling for ultraspectral imagery measurements of industrial smokestack emissions

The Telops Hyper-Cam midwave (InSb 1.5-5.μm) imaging Fourier-transform spectrometer observed the plume from a coal-burning power plant smokestack. From a distance of 600 meters, the plume was captured on a 128×64 pixel sub-window of the focal-plane array with each pixel imaging a 19.5×19.5cm2 region. Asymmetric interferograms were collected with long side and short side maximal optical path differences of 2.4cm and 0.9cm, respectively. Interferograms were recorded for each scan direction. The plume was strongly emissive across 1800-3000cm-1, and raw spectra revealed emissions from CO2, CO, H2O, NO, SO2, and HCl. A complete description of the instrument calibration and lineshape modeling is presented, including a simple and computationally efficient method of averaging spectra from forward- and reverse-scan interferograms that avoids the need to model a complex instrument lineshape. A simple radiative transfer model is developed to interpret the spectrum between 2565 ≤ ~ν ≤ 3000cm-1. Examination of the HCl spectrum demonstrates exceptional agreement between the data and an ideal instrument lineshape. For a pixel immediately above the stack exit, the plume temperature is estimated to be 399.6±0.6K with an SO2 concentration of 376±10ppmv, and these values agree well with in situ measurements of 407.0±0.2K and 383±2ppmv, respectively.

Direct Carboxamidation of Sydnones with Chlorosulfonyl Isocyanate

Abstract Various 4-carboxamido sydnones 2 can be prepared in good yield by reaction of the corresponding 3-substituted sydnones (cf. 1) with chlorosulfonyl isocyanate at room temperature.

Remote quantification of smokestack effluent mass flow rates using imaging Fourier transform spectrometry

A Telops Hyper-Cam midwave infrared (1.5 - 5.5μm) imaging Fourier-transform spectrometer (IFTS) was used to estimate industrial smokestack total effluent mass flow rates by combining spectrally-determined species concentrations with flow rates estimated via analysis of sequential images in the raw interferogram cube. Measurements of the coalburning smokestack were made with the IFTS at a stand-off distance of 350m. 185 hyperspectral datacubes were collected on a 128(W)×64(H) pixel sub-window (11.4×11.4cm2 per pixel) at a 0.5cm-1 spectral resolution. Strong emissions from H2O, CO2, CO, SO2, and NO were observed in the spectrum. A previously established single-layer radiative transfer model was used to estimate gas concentrations immediately above stack exit, and results compared reasonably with in situ measurements. A simple temporal cross-correlation analysis of sequential imagery enabled an estimation of the flow velocity at center stack. The estimated volumetric flow rate of 106±23m/s was within 4% of the reported value. Final effluent mass flow rates for CO2 and SO2 of 13.5±3.8kg/s and 71.3±19.3g/s were in good agreement with in situ rates of 11.6±0.1kg/s and 67.8±0.5g/s. NO was estimated at 16.1±4.2g/s, which did not compare well to the total NOx (NO +NO2) reported value of 11.2±0.2g/s. Unmonitored H2O, HCl , and CO were also estimated at 7.76±2.25kg/s, 7.40±2.00g/s, and 15.0±4.1 g/s respectively.

Temporally resolved infrared spectra from the detonation of advanced munitions

A suite of instruments including a 100 kHz 4-channel radiometer, a rapid scanning Fourier-transform infrared spectrometer, and two high-speed visible imagers was used to observe the detonation of several novel insensitive munitions being developed by the Air Force Research Laboratory. The spectral signatures exhibited from several different explosive compositions are discernable and may be exploited for event classification. The spectra are initially optically thick, resembling a Planckian distribution. In time, selective emission in the wings of atmospheric absorption bands becomes apparent, and the timescale and degree to which this occurs is correlated with aluminum content in the explosive formulation. By analyzing the high-speed imagery in conjunction with the time-resolved spectral measurements, it may be possible to interpret these results in terms of soot production and oxidation rates. These variables allow for an investigation into the chemical kinetics of explosions and perhaps reveal other phenomenology not yet readily apparent. With an increased phenomenological understanding, a model could be created to explain the kinetic behavior of the temperature and by-product concentration profiles and thus improve the ability of military sensing platforms to identify explosive types and sources.