Measurements of O (¹D) quenching rates in theFregion

Determinations of the quenching of O (¹D) atoms by N2 and O2 molecules in the F region have been made from observations of 6300-A night glow intensity enhancements produced by the Platteville 1.6-Mw transmitter. The heating of F region electrons near the point of reflection of the RF wave leads to electron impact excitation of oxygen atoms to the O (¹D) state. It is shown that at the lower altitudes the resulting region of enhanced 6300-A emission is localized to the region of electron energy absorption. At 225 km the measured time constants for intensity build-up following transmitter turn on and for intensity decay following turn off are identical and equal to (13 ± 1) sec. Time constants of 30–80 sec are found for the altitude range 260–300 km. The quenching frequency obtained at 225 km, referred to the altitude 120 km, is equal to (19 ± 2) sec−1, in agreement with less direct ionospheric determinations. The deduced quenching coefficient for the whole altitude range, 225–300 km, is kq = (6−3+4) × 10−11 cm³ sec−1 at 950°K, in good agreement with laboratory data.