SEARCH

SEARCH BY CITATION

Keywords:

  • carbon dioxide;
  • oxygen atoms;
  • vibrational relaxation

[1] Laboratory measurements of the quenching of CO2(ν2) by O atoms are presented over the 142–490 K temperature range relevant to the 75–120 km altitude region of the terrestrial atmosphere. The primary cooling mechanism in this region occurs when CO2 is efficiently excited through collisions with ambient O atoms, populating the bending vibrational (ν2) modes. A significant fraction of the vibrationally excited CO2 relaxes through spontaneous 15-μm emission that escapes into space, thereby removing kinetic energy from this region of the atmosphere and generating a local cooling effect. The rate coefficient for the vibrational relaxation of CO2(ν2) by O atoms, kO(ν2), is measured using transient diode laser absorption spectroscopy. A slight negative temperature dependence is observed for kO(ν2), with values ranging from 2.7 (±0.4) × 10−12 cm3 s−1 at 142 K to 1.3 (±0.2) × 10−12 cm3 s−1 at 490 K.