Detection of Nitrogen Atoms in the 2 s ( 2 p ) 3 3 s S 5 2 6 Metastable Autoionizing State

Metastable nitrogen atoms, produced by electron-impact dissociation of ${\mathrm{N}}_{2}$, have been detected in time-of-flight apparatuses located at Oregon State University and at University of California at Berkeley. Two different types of metastable atoms are detected; one type resembles Rydberg hydrogen atoms, while the other does not. The measured natural lifetime for the non-Rydberg atoms is 100 \ifmmode\pm\else\textpm\fi{} 25 \ensuremath{\mu}sec. Additional information regarding the identity of both types of metastable atoms is obtained by observing their quenching in a static electric field. The field-dependent decay constant for the Rydberg atoms is essentially a step function, and these atoms are entirely quenched by a field of 1.5 kV/cm. Both results are consistent with theory if the Rydberg atoms are in levels with principal quantum number greater than 25. The field-dependent decay constant for the non-Rydberg atoms varies quadratically with the strength of the applied electric field. In a field of 4 kV/cm applied along a 6-cm length of flight path, the value of this decay constant is 0.3 \ifmmode\times\else\texttimes\fi{} ${10}^{6}$ ${\mathrm{sec}}^{\ensuremath{-}1}$. The quenching results, together with the lifetime measurement, are a strong indication that the non-Rydberg atoms detected in the time-of-flight spectra are nitrogen atoms in the $2s{(2p)}^{3}3s^{6}S_{\frac{5}{2}}$ metastable autoionizing state.