Lawrence P. Giver

Intensity measurements of the CH4 bands in the region 4350 Å to 10,600 Å

Abstract The CH4 overtone bands from 4410 to 9990 A, long known in the spectra of the major planets, were studied at room temperature with a long-path, high-pressure White cell. Band intensities and profiles were measured, and are more complete than other recent laboratory measurements of these bands. Vibrational assignments of these bands are suggested, which are compatible with the assignments of the overtone bands longward of 1μ; these assignments imply that all the bands studied are combinations increasingly dominated at shorter wavelengths by v1, the symmetric stretch fundamental. In this self-consistent analysis, the weak band at 6825 A is assigned as 2v1+3v3, providing further laboratory evidence that it is probably not the 5v3 pure overtone that planetary astronomers had hoped it to be.

Intensity measurements and rotational intensity distribution for the oxygen A-band

Abstract Quantitative measurements of intensities and half-widths have been made for individual rotational lines of the atmospheric oxygen A-band. The total band intensity, as derived from the line intensity measurements, is 532 cm-1 km-1 atm-1 STP. The line half-widths at half intensity were determined by two methods for the PQ and PP branch lines and are found to vary from about 0.05 cm-1 atm-1 near the origin to 0.04 cm-1 atm-1 for high K″ values. The rotational intensity distribution is demonstrated to conform more closely to the theoretical Honl-London factors calculated by either Schlapp or by Watson rather than those found experimentally by Childs and Mecke.

Intensities and N2 collision-broadening coefficients measured for selected H2O absorption lines between 715 and 732 nm☆

Abstract Intensities and N2 collision-broadening coefficients were measured for 62 lines of H2O vapor between 715 and 732 nm. The lines selected are potentially useful for remote laser measurements of H2O vapor in the earths atmosphere. The spectra were obtained with several different H2O vapor abundances and N2 broadening gas pressures; the spectral resolution was 0.05 cm-1. Measured H2O line strengths range from 4 × 10-25 to 4 × 10-23 cm-1/(molec./cm2), and N2 collision broadening coefficients are approx. 0.1 cm-1/atm.

Nitric-acid band intensities and band-model parameters from 610 to 1760 cm −1

A set of 59 spectra of pure nitric acid was obtained at temperatures ranging from 236 to 294 K using path lengths from 10 to 50 cm and pressures from 0.05 to 1.1 Torr. No strong temperature dependencies were observed over the range of our measurements. Absorption coefficients and mean line-spacing parameters were determined at each 1-cm−1 interval in the three strong bands at 5.9, 7.5, and 1.3 μm by using a two-parameter random-band model. The resulting intensities for these bands are 1530 ± 100, 1383 ± 70, and 692 ± 35 cm−2 amagat−1, respectively. In addition, the absorption coefficients were determined in the three weak bands at 8.3, 13.2, and 15.5 μm. The band intensities derived are 44 ± 4, 45 ± 4, and 50 ± 5 cm−2 amagat−1, respectively.

Radiative flux measurements in the troposphere

The results of radiative flux-density measurements in the troposphere, made using an especially designed radiometer mounted on a Cessna 402B aircraft, are reported. The radiometer incorporates several well-known principles that result in highly accurate determinations of radiative fluxes in the atmosphere. Heating rates for gases and for aerosols are calculated, using measurements and radiosonde data. Instrument performance is verified by calculating the solar constant at the top of the atmosphere, using the radiative flux densities measured in the troposphere. Total heating rates of 0.175 and 0.377 K h(-1) are determined for hazy and foggy atmospheres, respectively. Aerosol heating rates of 0.065 and 0.235 K h(-1) are deduced from the total heating rates. Environmental noise measurements during data acquisition are presented. The solar constant value of 1387 +/- 21 W m(-2) derived from the experiments agrees within 4% of the standard value.

Intensity measurements, self-broadening coefficients, and rotational intensity distribution for lines of the oxygen B band at 6880 Å

Abstract Quantitative measurements of intensities and half-widths were made for individual rotational lines of the atmospheric oxygen B band. The total band intensity, as derived from the line intensity measurements, is 40·8±0·6 cm −1 km −1 atm −1 STP. As had been previously found in this laboratory for the oxygen A band, the relative line intensities conform closely to the rotational distribution calculated by either Schlapp or by Watson. The line half-widths at half-intensity were determined for oxygen self-broadening for the P Q and P P branch lines and for a few R Q and R R branch lines near the band origin, and were found to vary from 0·064 cm −1 atm −1 at J ′ = 1 to 0·042 cm −1 atm −1 at J ′ = 25.

Lightning production of hydrocarbons and HCN on Titan - Laboratory measurements

Many hydrocarbon species have been detected in the atmosphere of Titan. It is possible that lightning activity is occurring in the troposphere and that it contributes to the hydrocarbon inventory. Measurements of the chemical yields of hydrogen cyanide, acetylene, ethylene, ethane, and propane from simulated lightning discharges are reported. A comparison of the experimental results with those based on thermodynamic equilibrium assumptions shows significant disagreement and implies that theories based solely on thermodynamic equilibrium are inadequate. Although photochemistry and charged particle chemistry occurring in the stratosphere can account for many of the observed hydrocarbon species, the predicted abundance of ethylene is too low by a factor of 10 to 40. While some ethylene will be produced by charged-particle chemistry, the production of ethylene by lightning and its subsequent diffusion into the stratosphere appears to be an adequate source.

Water absorption line, 931–961 nm: selected intensities, N2-collision-broadening coefficients, self-broadening coefficients, and pressure shifts in air☆

Intensities were measured for 97 lines of H2O vapor between 932 and 961 nm. The lines were selected for their potential usefulness for remote laser measurements of H2O vapor in the earths atmosphere. The spectra were obtained with several different H2O vapor abundances and N2 broadening gas pressure; the spectral resolution was 0.046 cm−1 FWHM. Measured H2O line intensities range from 7 × 10−25 to 7 × 10−22 cm−1/molecules/cm2. H2O self-broadening coefficients were measured for 13 of these strongest lines; the mean value was 0.5 cm−1/atm. N2-collision-broadening coefficients were measured for 73 lines, and the average was 0.11 cm−1/atm HWHM. Pressure shifts in air were determined for a sample of six lines between 948 and 950 nm; these lines shift to lower frequency by an amount comparable to 0.1 of the collision-broadened widths measured in air or N2. The measured intensities of mainly lines of the 300-000 band are much larger than expected from prior computations, in some cases by over ab order if magnitude. Coriolis interactions with the stronger 201-000 band appear to be the primary cause of the enhancement of these line intensities.

On inhomogeneous scattering models of Titan's atmosphere

Abstract The spectrum of Titan from 4800 to 11 000 A has many CH4 absorption bands which cover a range of intensities of several orders of magnitude. Yet even the strongest of these bands in Titans spectrum has considerable residual central intensity. Some investigators have concluded that these strong CH4 bands must be highly saturated, but recent laboratory measurements of the bands made at room temperature show that curve-of-growth saturation is very small. At the presumed low pressures and temperatures in Titans atmosphere, we show that saturation is very dependent on the band model parameters. However, in either a simple reflecting layer model or in a homogeneous scattering model saturation cannot be the principal cause of the filling in of these strong CH4 bands if our best estimates of the band model parameters are correct. We find that an inhomogeneous scattering model atmosphere with fine “Axel dust” above most ot the CH4 gas is needed to fill in the band centers. The calculated spectrum of one particular model of this class is compared to observations of Titan. Our essential conclusion is that Titan does have most of its scattering particles above most of the CH4 gas which has an abundance of at least 2 km-am. This large abundance of CH4 is necessary to produce the 6420-A feature recently discovered in Titans spectrum.

Thermal infrared lines of methane broadened by nitrogen at low temperatures

Abstract Measurements of spectral transmittance in the v 4 -fundamental band of 12 CH 4 have been performed at low temperatures using a Fourier transform spectrometer with apodized spectral resolution of 0.06 cm -1 . With applications to lines formed in the atmospheres of Titan and Earth in mind, N 2 has been used as the broadening gas. Comparisons of observed and computed spectral transmittances on a line-by-line basis have yielded line strengths, N 2 -broadened half-widths and their variation with temperature. Best agreement between measured and computed spectra was obtained when the absolute intensity of the band was taken as 128 cm -2 -atm -1 at 296 K. Line widths were found to vary as T n with n = -1.0 for lines of the F -species and 0.63 for the A -species. Our measured line widths are considerably larger than those used in the AFGL compilation.