Steven J. Lipson

Highly rotationally excited NO(υ,J) in the thermosphere from CIRRIS 1A limb radiance measurements

Earthlimb spectra of thermospheric NO fundamental band emissions, obtained in the CIRRIS 1A Space Shuttle experiment, have been analyzed using nonlinear least-squares spectral fitting. Absolute NO(v{>=}1, J) column densities have been determined in the 100 to 260-km tangent height region and inverted to yield altitude-dependent number densities for both a rotationally thermalized and a high rotationally excited population component. Emissions from high-J levels are predicted to dominate the {Delta}v=2 overtone bands during the daytime. The rotationally excited population is found to decrease more at night than the rotationally thermalized component. In addition, radiance from the CO v=1{r_arrow}0 fundamental band is observed in the NO R-branch band head region, with greater relative importance at night. The derived CO rotational temperatures are significantly greater than modeled local kinetic temperatures. These results provide important inputs to models of NO(v, J) formation mechanisms, and of the chemistry, radiative processes, and energy budget of the thermosphere. 25 refs., 4 figs.

Observation of high-N hydroxyl pure rotation lines in atmospheric emission spectra by the CIRRIS 1A Space Shuttle Experiment

Pure rotation line emissions from highly rotationally excited OH have been observed between 80 and 110 km tangent height under both nighttime and daytime quiescent conditions. Data were obtained using the cryogenic CIRRIS 1A interferometer, operated on the Space Shuttle. Transitions from OH(v=0–2, N′≤33) were identified between 400 and 1000 cm−1, corresponding to states with energies as high as 23000 cm−1. These are the first definitive observations of OH pure rotation transitions in the air glow, and by far the highest N levels observed in any type of OH airglow emission spectrum. The present observations of highly excited rotational states of OH parallel those made during recent field studies of NO and laboratory studies of OH, NO, and CO.

Analysis of hydroxyl earthlimb airglow emissions: Kinetic model for state‐to‐state dynamics of OH (υ,N)

Detailed spectroscopic analysis of hydroxyl fundamental vibration-rotation and pure rotation emission lines has yielded OH(υ,N) absolute column densities for nighttime earthlimb spectra in the 20 to 110-km tangent height region. High-resolution spectra were obtained in the Cryogenic Infrared Radiance Instrumentation for Shuttle (CIRRIS 1A) experiment. Rotationally thermalized populations in υ = 1–9 have been derived from the fundamental bands between 2000 and 4000 cm−1. Highly rotationally excited populations with N ≤ 33 ( ≤ 2.3 eV rotational energy) have been inferred from the pure rotation spectra between 400 and 1000 cm−1. These emissions originate in the airglow region near 85–90 km altitude. Spectral fits of the pure rotation lines imply equal populations in the spinrotation states F1 and F2 but a ratio Π(A′):Π(A″) = 1.8±0.3 for the Λ-doublet populations. A forward predicting, first-principles kinetic model has been developed for the resultant OH(υ,N) limb column densities. The kinetic model incorporates a necessary and sufficient number of processes known to generate and quench OH(υ,N) in the mesopause region and includes recently calculated vibration-rotation Einstein coefficients for the high-N levels. The model reproduces both the thermal and the highly rotationally excited OH(υ,N) column densities. The tangent height dependence of the rotationally excited OH(υ,N) column densities is consistent with two possible formation mechanisms: (1) transfer of vibrational to rotational energy induced by collisions with O atoms or (2) direct chemical production via H + O3 → OH(υ,N) + O2.

Vibrational relaxation of OH(X 2Πi, v=1–3) by O2

Rate constants for OH(X 2Πi, v=1–3) vibrational relaxation induced by nonreactive collision with O2 have been measured. OH(v) is created by the H+O3 →OH(v≤9)+O2 reaction in an electron‐irradiated O3, H2, Ar mixture. OH(v) fundamental and first overtone IR emission is observed using time‐resolved Fourier spectroscopy. Spectral fitting followed by kinetic fitting of the resultant populations using a single‐quantum relaxation model yields rate constants of kv=1 =(1.3±0.4)×10−13, kv=2=(2.1±0.3)×10−13, kv=3=(2.9±0.8) ×10−13 (all units are in cm3 /s). Our measurements are consistent with and extend published results on the same system, as well as predictions made by Schwartz–Slawsky–Herzfeld theory.

Subthermal nitric oxide spin-orbit distributions in the thermosphere

The two NO(X{sup 2}{Pi}, v=1, {Omega}=1/2, 3/2) spin-orbit populations in the Earth`s thermosphere have been found to depart by more than a factor of 2 from the ratio expected from thermal equilibrium. The effective temperature describing the observed population distribution is as much as 700 K lower than the local kinetic temperature. Absolute NO(v=1, J, {Omega}) column densities were derived from high-resolution (1 cm{sup {minus}1}) infrared earthlimb spectra for tangent altitudes up to 200 km, obtained in the CIRRIS 1A Space Shuttle experiment. Nonlinear least-squares synthetic spectral fitting was used to analyze the NO {Delta}v=1 fundamental band emissions near 5.3 {mu}m. The spin-orbit distribution represents a third degree of freedom with the local kinetic temperature. These observations may significantly impact the interpretation of band-integrated measurements of NO in the upper atmosphere, for which equilibrium sublevel distributions have been assumed. The subthermal distribution is most likely produced in the collisional uppumping of NO(v=0) by O atoms, which is the major source of NO(v=1) in the thermosphere. This inference suggests that the present effect is related to the subthermal spin-orbit distributions observed in laboratory studies of NO{sub 2} photodissociation. 24 refs., 2 figs.

OH(ν,N) column densities from high-resolution Earthlimb spectra

Individual OH(ν,N) rotational state population column densities have been derived from spectral analysis of CIRRIS 1A nighttime earthlimb airglow data. Both pure rotation and vibration-rotation fundamental spectra have been examined, providing unique information on highly excited rotational states of OH(ν=0-6). The relative populations of the four spin sublevels have also been determined. These findings provide important insights into OH dynamics at the mesopause.

CIRRIS 1A observation of 13C16O and 12C18O fundamental band radiance in the upper atmosphere

Fundamental band emission from the ν=1 levels of isotopically substituted 13C16O and 12C18O has been observed for the first time in the earths atmosphere. High-resolution earthlimb spectra were obtained in the Cryogenic Infrared Radiance Instrumentation for Shuttle (CIRRIS 1A) experiment under both nighttime and daytime conditions. Spectral data between 70 and 150 km tangent height were analyzed in the 4.7 µm wavelength region, providing absolute 12C16O, 13C16O, and 12C18O column radiances. The minor isotope column radiances are up to 30 times more intense than predicted, based solely on the natural isotopic abundances of 13C and 18O. The derived line-of-sight radiances were accurately modeled using the Phillips Laboratory Atmospheric Radiance Code, and provide a strong test of radiative transport and excitation algorithms, as well as model climatologies.

Semiquantal modeling of thermal vibrational relaxation of diatomic molecules

Abstract Vibrationally excited molecules play an important role in the spectroscopy, energetics, and chemical behavior of a wide range of gaseous systems of scientific and applied interest. Unfortunately, many desired collisional relaxation rates have not yet been experimentally measured, and current theoretical methods are often inadequate or too cumbersome for practical application. We report a semiquantal two-parameter scaling method for predicting relaxation rates that is very simple to employ, and impressively fits the temperature and vibrational dependencies of quantum mechanical and experimental collisional relaxation rates for several diatomic molecules (e.g., N 2 , HF, OH, NO) over many orders of magnitude.