| The singlet-S state of atomic oxygen, O(1S), is responsible for the prominent 2972 A and 5577 A emissions in the terrestrial airglow. Production, mechanisms for O(1S) include photodissociation of O2, electron impact excitation of O, dissociative recombination of O2+, energy transfer from N2(A 3Sigmau+), the reaction N+O2 +, and chemiluminescence due to recombination of O2. Above 100km O(1S) is lost primarily by radiation. N2(A) experiences collisional deactivation by O below about 160 km.; Previous models for dayglow and auroral emissions of the N2 (A 3Sigmau+ → X 1Sigma g+) Vegard-Kaplan bands and O(1S), when based on laboratory rate coefficients, disagree with observations.; To solve this problem, the sources and sinks of O(1S) are considered using daytime aeronomical observations from 105 to 315 km and a numerical model. Middle ultraviolet spectra of the thermosphere were obtained from a sounding rocket and from a space shuttle payload. N2 Second Positive (2 PG) bands, N2 Vegard-Kaplan (VK) bands, and the OI 2972 A emission are extracted from the data using a least-squares multiple regression fit to synthetic spectra. A photoelectron and photochemical model is used to analyze the resulting vertical emission profiles.; The 2 PG band profiles indicate that photoelectron excitation of the N2 triplet system is modeled with an absolute uncertainty of +/-18%. The VK/2 PG intensity ratio suggests that laboratory rate coefficients for N2(A; v' = 0,1,2)+O should be increased by a factor of 1.77 to 2.34. However, the laboratory rates were measured at room temperature. When the effect of high thermosphere temperatures on collision frequency is accounted for, the rate coefficients for v' = 0, 1, and 2 are found to be (3.4 +/- 0.8) x 10-11 (T/298)1/2, (5.6 +/- 1.3) x 10-11 (T/298)1/2, and (4.8 +/- 1.2) x 10 -11(T/298)1/2cm3s-1 . At 298 K, these values are within 5% of the laboratory values for v' = 0 and 2 and within 40% of the laboratory values for v' = 1. The effective quantum yield of O( 1S) by N2(A)+O is found to be 0.47 +/- 17. This is within the error bars of previous work. The observations support a photoelectron cross section for O(1S) that is a factor of 2.0 larger than theoretical calculations but is consistent with laboratory work. |
