Mass Spectrometry of Free Radicals and Vibronically Excited Molecules Produced by Pulsed Electrical Discharges

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Abstract
Free radicals and metastable molecules produced by short‐duration pulsed electrical discharges have been studied with a mass spectrometer employing a collision‐free molecular‐beam sampling system. Nitrogen atoms generated by extremely short pulses (0.035‐μsec half‐width) have been used to study the dynamics of the gas‐sampling system. NH free radicals produced by electrical discharges in ammonia were detected in the X 3Σ− ground state and in the a 1Δ electronically excited state. It is estimated that approximately 22% of the NH radicals were in the a 1Δ state. Direct measurement of the ionization potential of NH in the ground state gives I (NH) = 13.1 eV. Vibronically excited nitrogen molecules from a discharge in a N2–He mixture have been observed with excitation energies up to about 9 eV, indicating that either or both of the metastable electronic states, a 1Πg and a′ 1Σu−, are substantially populated by the discharge. Evidence for excitation of N2 X 1Σg+ ground‐state molecules to high vibrational quantum numbers has been obtained from the appearance‐potential curve of the N2+ ion.

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