Spectroscopic Analysis of the N2 B3Πg − A3Σ+u in Radiation-Induced Air Ionization

Abstract

This article presents experimental results from probing atmospheric air irradiated by a Polonium-210 alpha particle source using both optical emission spectroscopy and continuous wave cavity ring down absorption spectroscopy to study the first positive (B³Π_g - A³Σ⁺_u) system of molecular nitrogen. Optical emission spectra were acquired between 11,000 and 17,391 cm ^-1 (575-900 nm). Long exposure measurements showed definitive emission from the first positive system, atomic nitrogen, atomic oxygen, and atomic argon. A non-Boltzmann emission model was constructed and fit to the data to infer relative vibrational state populations of N₂(B³Π_g). In pursuit of more quantitative characterization of the plasma, cavity ring down absorption measurements were performed between 12,800 and 13,070 cm^-1 (765-781 nm) using an external cavity diode laser targeting detection and quantification of electronically excited molecular nitrogen N₂(³Σ⁺_u). The null result in this measurement provides experimental evidence that in atmospheric pressure air, the presence of N₂(A³Σ⁺_u) generated by alpha particle radiation is below the estimated 0.4 ppb detection limit of the experiment.