AFGL atmospheric absorption line parameters compilation: 1982 edition

High resolution IR diode laser study of collisional energy transfer between highly vibrationally excited monofluorobenzene and CO2: the effect of donor fluorination on strong collision energy transfer

Collisional energy transfer between vibrational ground state CO2 and highly vibrationally excited monofluorobenzene (MFB) was studied using narrow bandwidth (0.0003 cm(-1)) IR diode laser absorption spectroscopy. Highly vibrationally excited MFB with E' = ∼41,000 cm(-1) was prepared by 248 nm UV excitation followed by rapid radiationless internal conversion to the electronic ground state (S1→S0*). The amount of vibrational energy transferred from hot MFB into rotations and translations of CO2 via collisions was measured by probing the scattered CO2 using the IR diode laser. The absolute state specific energy transfer rate constants and scattering probabilities for single collisions between hot MFB and CO2 were measured and used to determine the energy transfer probability distribution function, P(E,E'), in the large ΔE region. P(E,E') was then fit to a bi-exponential function and extrapolated to the low ΔE region. P(E,E') and the biexponential fit data were used to determine the partitioning between weak and strong collisions as well as investigate molecular properties responsible for large collisional energy transfer events. Fermi's Golden rule was used to model the shape of P(E,E') and identify which donor vibrational motions are primarily responsible for energy transfer. In general, the results suggest that low-frequency MFB vibrational modes are primarily responsible for strong collisions, and govern the shape and magnitude of P(E,E'). Where deviations from this general trend occur, vibrational modes with large negative anharmonicity constants are more efficient energy gateways than modes with similar frequency, while vibrational modes with large positive anharmonicity constants are less efficient at energy transfer than modes of similar frequency.

Analysis of the Interacting Octad System of (12)CH(4)

The octad system of methane (12)CH(4) has been analyzed with a fourth-order (459 parameters) Hamiltonian for energy levels and a third-order (28 parameters) dipole moment expansion for infrared intensities. Nearly 8000 assigned positions and 2500 measured line intensities (obtained with the Fourier transform spectrometer located at Kitt Peak National Observatory/National Solar Observatory) have been considered in the modeling. Infrared (Octad-Ground State) and hot bands (Octad-Dyad) data have been used. While the model does not reproduce the measurements at their inherent experimental precisions, it has been sufficient to interpret and substantially assign this spectral region of methane for the first time in over 30 years of investigation. Copyright 2001 Academic Press.

Influence of CO2-laser linewidth on the measured absorption coefficients of atmospheric water vapor and ammonia

We describe the results of analysis of the experimental and calculated data on the water vapor and ammonia absorption coefficients of CO2-laser radiation. We believe that the different halfwidths of CO2-laser lines, caused by different pressures of the working mixtures in specific experiments, are probably the reason for discrepancies between data presented in various papers.

1995 Atmospheric Trace Molecule Spectroscopy (ATMOS) linelist

The Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment uses a Fourier-transform spectrometer on board the Space Shuttle to record infrared solar occultation spectra of the atmosphere at 0.01-cm(-1) resolution. The current version of the molecular spectroscopic database used for the analysis of the data obtained during three Space Shuttle missions between 1992 and 1994 is described. It is an extension of the effort first described by Brown et al. [Appl. Opt. 26, 5154 (1987)] to maintain an up-to-date database for the ATMOS experiment. The three-part ATMOS compilation contains line parameters of 49 molecular species between 0 and 10000 cm(-1). The main list, with nearly 700,000 entries, is an updated version of the HITRAN 1992 database. The second compilation contains supplemental line parameters, and the third set consists of absorption cross sections to represent the unresolvable features of heavy molecules. The differences between the ATMOS database and other public compilations are discussed.

Analysis of the influence of O(2) A-band absorption on atmospheric correction of ocean-color imagery

Two satellite-borne ocean-color sensors scheduled for launch in the mid 1990's each have a spectral band (nominally 745-785 nm) that completely encompasses the O(2) A band at 762 nm. These spectral bands are to be used in atmospheric correction of the color imagery by assessment of the aerosol contribution to the total radiance at the sensor. The effect of the O(2) band on the radiance measured at the satellite is studied with a line-by-line backward Monte Carlo radiative transfer code. As expected, if the O(2) absorption is ignored, unacceptably large errors in the atmospheric correction result. The effects of the absorption depend on the vertical profile of the aerosol. By assuming an aerosol profile-the base profile-we show that it is possible to remove most of the O(2)-absorption effects from atmospheric correction in a simple manner. We also investigate the sensitivity of the results to the details of the assumed base profile and find that, with the exception of situations in which there are significant quantities of aerosol in the stratosphere, e.g., following volcanic eruptions or in the presence of thin cirrus clouds, the quality of the atmospheric correction depends only weakly on the base profile. Situations with high concentrations of stratospheric aerosol require additional information regarding vertical structure for this spectral band to be used in atmospheric correction; however, it should be possible to infer the presence of such aerosol by a failure of the atmospheric correction to produce acceptable water-leaving radiance in the red. An important feature of our method for removal of the O(2)-absorption effects is that it permits the use of lookup tables that can be prepared in the absence of O(2) absorption by the use of more efficient radiative transfer codes.

Measurements of air-, N(2)-, and O(2) -broadened halfwidths and pressure-induced line shifts in the v(3) band of (13)CH(4)

Air-, nitrogen-, and oxygen-broadened halfwidth and pressure-induced line shift coefficients have been measured for over seventy-five individual vibration-rotation transitions in the v(3) fundamental band of (13)CH(4)at 3 mum from room temperature IR laboratory absorption spectra recorded at a 0.01-cm(-1) resolution with a Fourier transform spectrometer. Transitions up to J" = 13 in the P-branch and J" = 7 in the R-branch were analyzed using a nonlinear least-squares curve fitting technique assuming a Voigt line shape. From the analysis, we have determined the mean ratios of air- to nitrogen-broadened and air- to oxygen-broadened halfwidth coefficients obtained for the same transitions as 1.00 +/- 0.03 and 1.06 +/- 0.04, respectively. The measured pressure shift coefficients were predominantly negative, and the mean and standard deviation values for air-, nitrogen-, and oxygen-broadened shifts were -0.0067 +/- 0.0032, -0.0068 +/- 0.0041, and -0.0066 +/- 0.0028 cm(-1) atm(-1), respectively. Comparisons are made with the results obtained for similar transitions in the v(3) band of (12)CH(4) and the v(4) band of (13)CH(4).

Photoacoustic technique for the measurement of absorption line profiles

A spectrophone utilizing a resonant cylindrical cavity and operated by driving the first azimuthal mode of the cavity has been developed for the study of weak absorption lines of gases at pressures from 100 to 1300 Torr. Presented are the acoustic resonant amplification factor as a function of pressure, and a description of the noise sources inherent in this spectrophone. An example is given of the optical frequency resolution resulting when this spectrophone is used in conjunction with a tunable ring dye laser as a high resolution spectrometer.

Atmospheric backscatter vertical profiles at 9.2 and 10.6 microm: a comparative study

We report a series of atmospheric aerosol backscatter measurements at two widely spaced CO(2) laser wavelengths: 9.25 and 10.6 microm. Comparisons are made beween backscatter coefficient profiles at these two wavelengths up to 20-km altitude. Measurements such as those reported here can be used to assess the feasibility of coherent CO(2) lidar for wind measurements, and they also provide a partial test of backscatter model predictions.

Measured line positions and strengths of methane between 5500 and 6180 cm(-1)

The positions and strengths of more than 2000 methane absorption lines stronger than 1.0 x 10(-4) cm(-2) atm(-1) have been measured in the 5500-6180-cm(-1) spectral region. The measurements were made using spectra recorded at room temperature (296 K) with a resolution of 0.01 cm(-1). The spectra were obtained using the Fourier transform spectrometer at the McMath solar telescope at the Kitt Peak National Observatory. The 2nu(3) band strength of (12)CH(4) was determined to be 1.641 cm(-2) atm(-1); a Herman-Wallis-type correction was also determined to be (1 + 0.0298 m + 0.000536 M(2)).

Retrieval of constituent mixing ratios from limb thermal emission spectra

An onion-peeling iterative, least-squares relaxation method to retrieve mixing ratio profiles from limb thermal emission spectra is presented. The method has been tested on synthetic data, containing various amounts of added random noise for O(3), HNO(3), and N(2)O. The retrieval method is used to obtain O(3) and HNO(3) mixing ratio profiles from high-resolution thermal emission spectra. Results of the retrievals compare favorably with those obtained by others.

Radiometer based on the principle of Zeeman modulation designed for the measurement of NO in the atmosphere

The principles, construction, and operation of a novel gas correlation spectrometer employing the Zeeman effect to perform selective modulation are described. The retrieval of column amounts of atmospheric nitric oxide (NO) is discussed. The sun is used as an IR source, and the radiation is modulated by the splitting of absorption lines in a sample of NO gas which is positioned in a variable longitudinal field. A sample of the results obtained at a high altitude observatory is presented. The diurnal variation in the observed NO column is consistent with photochemical predictions. Unexpected shorter term variabilities which are observed may be dynamic effects but are more likely to be instrumental artifacts. The instrument is insensitive to tropospheric NO, making it potentially useful for long term monitoring from the ground of NO in the stratosphere and mesosphere.

Trace gas detection with short-external-cavity InGaAsP diode laser transmitter modules operating at 1.58 microm

Detection of CO(2) and CO at 1.58 microm (6322 cm(-1)) using an InGaAsP diode laser and mode control is described.Mode control is a technique whereby a short cavity, external to the laser, is used to force the laser to operate in a single mode. By monitoring the voltage across the terminals of the laser and using electronic feedback it is possible to optimize continually the external cavity so that the laser operates reliably in the mode of choice for scans >3.5 cm(-1). This technique offers the possibility of high-sensitivity detection over a region of ~30 cm(-1) with continuous coverage in overlapping sections of ~3 cm(-1) with conventional (and hence inexpensive) multimode diode lasers.