The N₂ + O⁺ charge‐exchange reaction and the dayglow N₂⁺ emission

Abstract

Abstract. Dayglow spectra were recorded by the Arizona Airglow Experiment from the payload bay of the shuttle, STS-74. These spectra are used to reexamine the role of the prominent N2 + first negative emission from the dayglow thermosphere. Many reports of the N2 + emissions identify problems in validating the intensity of the emission. Also, an extended vibrational and rotational structure of the bands remains unexplained in the historical analysis. These anomalies appear to be due to the charge-exchange reaction, N2+O+(2D,2p)-• N2++O, which is the dominant source of N2 + ions in the sunlit atmosphere at high altitudes. In the present work the N2 + emission was considered to originate from two separate ion sources. First are those emissions originating from ions produced by photoionizaton and electron bombardment; these emissions can be modeled. Second are the emissions originating from ions produced by the charge-exchange reaction; these emissions cannot be modeled. Synthetic emission profiles due to the first ion source were modeled and subtracted from the observed spectrum, leaving emission profiles resulting from the charge-exchange ion source. These residual vibrational and rotational profiles were analyzed to retrieve resonance scattering rates for these ions. These scattering rates can be used to estimate the N2 + first negative emission rate expected from the thermosphere with a model of the

Color Ratios of Subauroral (STEVE) Arcs

“…Enhancing N 2 + 1 N without similarly increasing 557.7 nm would be difficult to accomplish with direct particle excitation. It is possible that (1) a large fraction of the hot O + ions could be in the 2D and 2P states, and these could charge exchange with atmospheric N 2 producing ground state N 2 + ions (Broadfoot & Stone, 1999). Then only low-energy, few eV electrons would be needed to excite the N 2 + ions into the upper state of the 1 N band.…”

Evaluation of electron impact excitation of N2 X 1Σg+(0) into the N2+ X 2Σg+(v), A 2Πu(v), and B 2Σu+(v) states

“…When sunlit aurora extends to high altitude (up to 700∼1100 km), resonant scattering of solar radiation by N 2 + via the B 2 Σ u + − X 2 Σ g + transition produces an abnormally bright blue color in sunlit aurorae [ Bates , 1949; Hunten , 2003]. Charge exchange of N 2 with O + ( 2 D) and O + ( 2 P) also plays an important role in the production of N 2 + (B 2 Σ u + ) [ Broadfoot and Stone , 1999]. The brightness of the first negative (0,0) band is frequently observed in the kiloRayleigh range [ Romick et al , 1999].…”

Thermospheric neutral temperatures derived from charge-exchange produced N<sub>2</sub><sup>+</sup> Meinel (1,0) rotational distributions

“…The kinetic module (Lummerzheim and Lilensten, 1994) Ionization of N 2 is accomplished by three primary means: electron impact, and by photoionization and resonant scattering under sunlit conditions. An additional means of selective ionization is provided through charge-exchange reactions between O + and N 2 (Broadfoot, 1967;Broadfoot and Stone, 1999). Espy et al (1987), on the basis of excess populations of N + 2 (A 2 u , ν = 1) ions in comparison with ν = 0, 2 ions, have provided strong support that in aurora, the resonant charge exchange shown in Reaction (R1) selectively populates the ν = 1 level.…”