Dr. James A. Dodd Profile

Dr. James A. Dodd

Deputy Chief Scientist

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Proceedings Article | 1 November 2005 Paper

Room temperature measurements of CO₂(v₂)-O vibrational energy transfer

Karen Castle, Katherine Kleissas, Justin Rhinehart, Eunsook Hwang, James Dodd

Proceedings Volume 5979, 597910 (2005) https://doi.org/10.1117/12.627073

KEYWORDS: Carbon monoxide, Absorption, Xenon, Photolysis, Energy transfer, Chemical species, Semiconductor lasers, Gas lasers, Temperature metrology, Oxygen

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In the Earth's upper atmosphere, collisions between ground state CO₂ molecules and translationally excited O atoms effectively populate the bending (v₂) vibrational modes of CO₂. Subsequent relaxation of the v₂ modes occurs through spontaneous or stimulated emission of 15-μm radiation. Much of this radiation escapes into space, thereby removing ambient kinetic energy from the atmosphere. This cooling mechanism is especially important at altitudes between 75 and 120 km where the O atom density is relatively high and the conditions are optically thin. We have performed laboratory measurements to better characterize the vibrational energy transfer efficiency for this system. Several improvements to the experiment have been made since our preliminary manuscript on this topic. The temperature-jump method is used to form vibrationally excited CO₂, and transient diode laser absorption spectroscopy is used to monitor the vibrational level populations following collisions with atomic oxygen. Using this approach, the room-temperature vibrational relaxation rate coefficient, k_O(v₂), has been measured to be (2.0±0.3)x10^-12 cm³s^-1. This value is slightly higher than previous laboratory measurements, which have clustered in the (1-1.5)x10^-12 cm³s^-1 range, and on the low end of aeronomical estimates of (2-6)x10^-12 cm³s^-1.

Proceedings Article | 16 February 2004 Paper

Laboratory studies of CO2(nu2)-O vibrational energy transfer

Karen Castle, Eunsook Hwang, James Dodd

Proceedings Volume 5235, (2004) https://doi.org/10.1117/12.515423

KEYWORDS: Carbon monoxide, Absorption, Chemical species, Gas lasers, Photolysis, Energy transfer, Semiconductor lasers, Temperature metrology, Xenon, Argon

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For altitudes above about 80 km, oxygen molecules are increasingly dissociated by solar vacuum ultraviolet absorption, and O atoms, together with N₂, become a principal constituent of the atmosphere. Through collisions with the ambient O atoms, the ground vibrational state of CO₂ is efficiently excited to its lowest excited vibrational state, with one quantum of energy in the ν₂ bending mode. In the near-space environment, a sizable fraction of this population relaxes via 15-μm spontaneous infrared emission, which effectively converts ambient kinetic energy into radiative energy that passes into space. This process is the principal upper atmospheric cooling mechanism in the 75-120 km altitude range. Despite the importance of this mechanism, current estimates of the CO₂(ν₂)-O vibrational relaxation rate constant k_O(ν₂) vary over a factor of six, with the laboratory measurements clustering in the 1-1.5 × 10^-12cm³s^-1range, and the aeronomical estimates in the 3-6 × 10^-12cm³s^-1range. We are currently pursuing vibrational relaxation measurements on the CO₂(ν₂)-O system in the laboratory, using the temperature jump method together with transient diode laser absorption spectroscopy detection of the CO₂ vibrational level populations. We will present the current state of progress of the experimental effort, as well as possible future directions.

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