Vibrationally excited nitric oxide in the upper atmosphere

Vibrational levels of the ground states ((2)pi (1/2), 3/2) of nitric oxide are populated by transfer of vibrational quanta in collisions with molecular oxygen and nitrogen; by atom exchange with atomic oxygen; by absorption of infrared radiation from the earth's surface, the lower atmosphere, and the sun; by fluorescent decay of the beta-, gamma-, and delta-band systems following resonance absorption of solar ultraviolet radiation; by electron impact excitation; and during chemical formation. These excitation mechanisms are balanced by collisional deexcitation and by radiation in the infrared vibration rotation bands. The relative importance of each of these processes is assessed for quiescent day and night conditions and for aurorae. In the absence of collisional interactions, absorption of terrestrial infrared radiation maintains a vibrational temperature of between 220 K and 270 K near the mesopause.