S.S. Penner

Absorption coefficients for water vapor in the 600–1000 cm-1 region

Abstract Experimental determinations of absorption coefficients of water vapor are presented for temperatures between 400 and 500°K and pressures of 2 and 10 atm. All measurements were made by using the technique of self-broadening, moderate resolution (≈ 25 cm -1 ), and a supply source of liquid water at variable temperatures. The observed results are consistent with the idea that hydrogen bonding contributes to the absorption coefficient of water vapor in the spectral region between 600 and 1000 cm -1 .

Absolute infrared intensity measurements on the fundamental of NO

Abstract The integrated intensity for the fundamental vibration-rotation band of NO has been redetermined, using the method of self-broadening. The cell length was measured by performing an absolute calibration experiment with CO, the integrated intensity (α CO ) of which was assumed to have the value α CO = 237 cm -2 -atm -1 at room temperature. Our best estimate for α NO is 128 ± 10 cm -2 -atm -1 at S.T.P.

Spectroscopic studies of hydrogen bonding in H2S

Abstract The energy of hydrogen bonding in the gas phase has been estimated for H 2 S from quantitative infrared intensity measurements in the 4 μ region. Our value of 1·7±0·3 kcal/mole may be considered to be in excellent agreement with the result of theoretical calculations (1·8 kcal/mole) by Fyfe (4) in view of uncertainties in both the calculated and measured values.

Effect of (partial) overlapping of spectral lines on the total emissivity of H2O-CO2 mixtures (T⪞800°K)

Abstract The influence of (partial) overlapping of lines in CO 2 -H 2 O mixtures has been calculated. Highly simplified calculations lead to acceptable agreement with Hottels empirical correlations at elevated temperatures ( T =1200°K) where only the 2·7 μ bands of H 2 O and CO 2 are overlapped. On the other hand, comparisons at 811°K indicate that serious discrepancies exist in the 15 μ region between Hottels correlations and approximate calculations based on recent spectroscopic measurements.

Approximate band absorption and total emissivity calculations for CO2

Abstract A highly simplified procedure, using symmetrical band contours and intensity estimates derived from harmonic oscillator approximations, has been used to calculate band and total emissivities for CO2. Agreement with experimental data and with more accurate calculations is excellent.

Approximate calculations of spectral absorption coefficients in infrared vibration-rotation spectra

Abstract The limitations involved in the use of nearly profiles for individual vibration rotation bands are examined for CO and CO 2 . Although the harmonic-oscillator approximation is useful in estimations of band emission or band absorption, large errors are normally obtained in calculations of spectral absorption coefficients because first-order effects on ground-state populations are produced by anharmonicities at all wavenumbers except those lying very close to the band centers. Inclusion of first-order corrections for low and moderate rotational energies yields good results for the spectral absorption coefficients of CO and CO 2 at 300 and 1200°K. Furthermore, our simplified theoretical formulae provide an acceptable description for previously published spectral-absorption-coefficient profiles for the fundamental and first-overtone bands of CO at room temperature.

Measurements of f-numbers for α- and γ-bands of TiO☆

A pressure-driven shock tube has been used to measure electronic f-numbers for bands (three each) belonging to the α- and γ-band systems of titanium oxide. Observations were made at wavelengths of 6734 A, 7147 A, and 7689 A in the γ-bands, and at 4969 A, 5183 A, and 5460 A in the γ-bands. Observed variations in the f-numbers for a given electronic band system may perhaps be attributed to the interaction between vibrational and electronic motion. The TiO was produced in situ behind reflected shock waves by reaction between TiCl4 and O2 in Ar. The initial gas mixture contained, per mole of mixture, 0·0025 mole of TiCl4, 0·010 (or 0·004 or 0·053) mole of O2 and 0·9875 (or 0·9935 or 0·9445) mole of Ar. Incident chock-wave velocities between 1·4×105 and 1·7×105 cm/sec were used; the corresponding calculated equilibrium gas temperatures behind the reflected shock waves were found to be between 3000°K and 6000°K, respectively. An expression for the absorption coefficient of TiO was derived by using the just-overlapping line model. For the experimental conditions encountered in our studies, use of this model gives adequate results. The resulting f-number estimates for the γ- and α-bands are summarized in Tables 2 and 4, respectively, at various wavelengths and temperatures. For the γ-bands, our results for the f-number lie between 0·089 and 0·19, whereas the measured range of values for the α-bands extends from 0·030 to 0·052.

Intensity and collision half-width measurements using a laser source—II. Continuum and line absorption of Br2 at 6328 A

Abstract Absorption measurements have been performed on Br2 vapor at 15 798·00±0·07 cm-1 by using an He-Ne laser as light source. Systematic studies at pressures between about 0·25 and 1·75 atm, and at a temperature of 373±2°K, have yielded the following estimates: continuum absorption coefficient ⋍ 0·113 cm-1 -atm-1; integrated intensity ⋍ 4·6 x 10-3 cm-2-atm-1 for the R(44) line of Br81Br79 in the υ′ = 11 → υ′ = 5 band of the 1Σ+g → 3ΠOu+ band system of Br2; mean collision line half-width of Br2 lines near the laser frequency ⋍ 0·07 cm-1-atm-1. The error estimates are ± 10 per cent for the continuum absorption coefficient; the bounds on S1 are 3·5 x 10-3 ⩽ S1, cm-2 atm-1 (at 373°K) ⩽ 8·2 x 10-3 whereas those on b1 are 0·07 ⩽ b1, cm-1 atm-1 (at 373°K) ⩽ 0·11. The limit estimates for the line properties involve the assumption that the applicable overlap-integral ratios are all equal to unity.

On the determination of log-normal particle-size distributions using half widths and detectabilities of scattered laser power spectra

Abstract We present the theoretical curves needed to define log-normal particle-size distributions from the measured power spectra of scattered laser radiation. (i) We show how to make estimates of the particle sizes of monodisperse systems using only the measured half-widths of the observed, scattered laser-power spectra. This technique has been employed by us before on flat-flame burners and does not involve the optical properties of the scattering centers. Number densities of particles may also be determined readily for monodisperse systems but require use of the index of refraction for the scattering centers. (ii) We define procedures for making estimates of the count-median diameters and standard deviations in log-normal size distributions using (a) measured half-widths of scattered laser-power spectra and (b) measured ratios of detectabilities determined for a given laser at two different scattering angels. We find that it is not possible to achieve adequate sensitivity for experimental utilization of this technique. (iii) We describe techniques for estimating the count-median diameters and standard deviations in log-normal size distributions using (a) measured half-widths of scattered laser-power spectra and (b) measured ratios of detectabilities determined at the same or at different scattering angles for two different laser wavelengths. Our calculations indicate that these procedures will also not yield adequate sensitivities for the determinations of particle-size distributions. (iv) The use of two linearly polarized beams [one polarized in the plane defined by the direction of laser-beam propagation and the vertical direction (1) and the other defined by the direction of laser-beam propagation and the horizontal (2)] in making half-width and detectability measurements has been studied. Although acceptable sensitivities for the determination of σ g and ♂r are achievable for selected particle-size ranges, the use of polarized laser radiation will not always lead to satisfactory characterization of log-normal particle-size distributions. Experiments involving detectabilities do not offer clear-cut advantages over those involving half-widths insofar as measurement sensitivities are concerned. (v) We describe procedures for determination of the total number of particles contained in the log-normal particle-size distributions using measured absolute values for the detectabilities observed for the power spectra of scattered laser radiation, after prior definition of the count-median diameters and standard deviations in log-normal size distributions.

Comparison of a multiple-slit correlation spectrometer with laser absorption in air-pollutant detection☆

Abstract The use of tunable-diode lasers in air-pollution diagnostics at selected centers of absorbing lines should produce an increase of 104 in sensitivity, without loss in selectivity, as compared with correlation spectroscopy.