Engineering topics

Anderson, Stuart M.

Publications and source records attributed to Anderson, Stuart M..

6 records

NASA NTRS1993

Ozone absorption cross section measurements in the Wulf bands

A tandem dual-beam spectrometer has been developed to determine ozone absorption cross sections for 13 selected wavelengths between 750 and 975 nm at room temperature. The increasingly pronounced structure in this region may interfere with atmospheric trace gas transitions that are useful for remote sensing and complicate the measurement of aerosols. Ozone concentrations were determined by absorption at the common HeNe laser transition near 632.8 nm using the absolute cross section reported previously. The overall accuracy of these room temperature measurements is generally better than 2 percent. A synoptic near-IR spectrum scaled to these measurements is employed for comparison with results of previous studies.

Anderson, Stuart M.↗

NASA NTRS1993

Rotational structure in the near-infrared absorption spectrum of ozone

The lowest energy members of the near-IR absorption bands of ozone possess fine structure which is probably due to the rotation of the molecule in the upper vibronic state, suggesting that this state is metastable. A preliminary analysis of the structures as rotational subbands supports a recent theoretical assignment of the near-IR vibronic features to the 3A2 - 1A1 electronic transition. A binding energy of about 0.1 eV is inferred from the breakoff in the observed structure.

Anderson, Stuart M.↗

NASA NTRS1992

Laser measurements of ozone absorption cross sections in the Chappuis band

A sensitive spectrometer has been developed that exploits several He-Ne laser transitions in the visible for precise, high resolution measurements of Chappuis band ozone absorption cross sections at room temperature. An overall uncertainty of better than one percent has been achieved through a combination of transducer calibrations and an experimental technique that unambiguously determines the impurity content of each ozone sample. Results compare favorably with those from most previous analyses in the visible range, though some are obviously lower than this consensus due probably to errors in ozone density measurements.

Anderson, Stuart M.↗

NASA NTRS1991

Effect of isotopic substitution on the visible absorption spectrum of ozone

Gas-phase spectra for (O-16)3 and (O-18)3 are examined to consider the electronic states which cause the Chappuis bands. Specifications of the spectrometer and spectra calibrations are given. The results of both a conventional description of the vibrational structure and an examination of the autocorrelation functions are discussed. Transitions to two electronically excited states are the significant features of the isotope shifts. The transitions are characterized by adiabatic energies about 750/cm apart, and the higher energy approaches 16,400/cm. The vibrational structure of the higher state accompanies a relatively simple progression, and the lower state accompanies one isolated band. The autocorrelation analysis shows that for (O-16)3, major recurrences near 31 and 41 fs are found, and longer equivalent times are found for (O-18)3. At longer times, minor recurrences are also found. The results are considered significant for the understanding of the electronic and vibrational structures of the Chappuis bands. Suggestions for future work based on these results are discussed.

Anderson, Stuart M.↗

NASA NTRS1991

Open-path tunable diode laser absorption for eddy correlation flux measurements of atmospheric trace gases

Biogenic emissions from and dry deposition to terrestrial surfaces are important processes determining the trace gas composition of the atmosphere. An instrument has been developed for flux measurements of gases such as CH4, N2O, and O3 based on the eddy correlation technique which combines trace gas fluctuation measurements with simultaneous windfield measurements. The instrument combines a tunable diode laser infrared light source with an open-path multipass absorption cell in order to provide the fast time response and short base pathlength required for the eddy correlation method. Initial field tests using the instrument to measure methane emissions from a local wetland demonstrate the capability for high precision eddy correlation flux measurements.

Anderson, Stuart M.↗

NASA NTRS1987

Comment on 'Heavy ozone in the stratosphere'

It is suggested that the factor-of-two difference in ozone formation rate constants derived by Bates (1986) can also be explained by the omission of standard correction factors from the rate expression. Proper accounting for the fact that isotope exchange and recombination reactions share a common energized collision complex (which can decay by dissociation to products isotopically distinct from the original reactants) eliminates the anomalous dependence of the rate constant on the isotopic composition of the reactants and products through their symmetry numbers. In a reply, Bates argues that symmetry effects in association do not lead to enhancement of the total heavy ozone abundance.

Anderson, Stuart M.↗