This project is concerned with developing basic data on atomic and molecular nitrogen that is needed to better understand energy flow and chemistry in the upper atmosphere. Electron impact dissociation and photodissociation of molecular nitrogen produce atomic nitrogen in either the ground state N(4S) or in one of its excited states, N(2D) or N(2P). The reactivity of atomic nitrogen and its role in the odd nitrogen cycle depends sensitively upon the state of excitation of the nitrogen atom. Changes by 100% in thermospheric NO concentrations are predicted when the ratio of ground to excited states produced in dissociation is varied from 50:50 to 46:54. While a ratio of 50:50 is assumed on theoretical grounds, the ratio itself has never been determined experimentally. The principle investigator has developed a novel technique that permits direct measurement of the excitation state of both nitrogen atoms produced in N2 dissociation. The measurement is carried out in a fast beam of nitrogen molecules using laser excitation to study excited states of N2 in the region from 10 to 18 eV. This technique will be used to determine precisely the rate of predissociation of excited states of N2 and the state of excitation of the atomic nitrogen products formed. Branching ratios to N(4S), N(2D), and N(2P) are then obtained by summation over all the states involved in photodissociation and electron impact dissociation of N2.
