The N(^2D - ^4S) 520 nm forbidden doublet transition in the nightglow: An experimental test of the theoretical intensity ratio

Details The N(^2D - ^4S) 520 nm forbidden doublet transition in the nightglow: An experimental test of the theoretical intensity ratio The N(^2D - ^4S) 520 nm forbidden doublet transition in the nightglow: An experimental test of the theoretical intensity ratio

Apr 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja.....1618s&link_type=abstract

EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #1618

Astronomy and Astrophysics

Astronomy

Scientific paper

N(^2D) is an important species in the nighttime ionosphere, as its reaction with O_2 is a principal source of NO. Its modeled concentration peaks near 200 km, at approximately 4 × 10^5 cm-3. Nightglow emission in the optically forbidden lines at 519.8 and 520.0 nm is quite weak, a consequence of the combination of an extremely long radiative lifetime, about 10^5 sec, and quenching by O-atoms, O_2, and N_2. The radiative lifetime is known only from theory, and various calculations lead to a range of possible values for the intensity ratio R = I(519.8)/I(520.0) of 1.5-2.5. On the observational side, Hernandez and Turtle [1969] determined a range of R = 1.3-1.9 in the nightglow, and Sivjee et al. [1981] reported a variable ratio in aurorae, between 1.2 and 1.6. From sky spectra obtained at the Keck II telescope on Mauna Kea, we have accumulated eighty-five 30-60 minute data sets, from March and October, 2000, and April, 2001, over 13 nights of astronomical observations. We find R to have a quite precise value of 1.760± 0.012 (2-σ). There is no difference between the three data sets in terms of the extracted ratio, which therefore seems to be independent of external conditions. At the same time, determination of the O(^1D - ^3P) doublet intensity ratio, I(630.0)/I(636.4), gives a value of 3.03 ± 0.01, the statistical expectation. G. Hernandez and J. P. Turtle, Planet. Space Sci. 17, 675, 1969. G. G. Sivjee, C. S. Deehr, and K. Henricksen, J. Geophys. Res. 86, 1581, 1981.

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