Detection of the a 1Πg (v′=0, 1)←X 1Σ+g (v″=0) transition in N2 by laser-induced fluorescence

Abstract

The a¹Π_g(v′=0.1)←X¹Σ⁺_g(v″=0) transitions in N₂, part of the Lyman–Birge–Hopfield bands, have been seen by two‐photon absorption detected by VUV fluorescence. Fluorescence was observed over a pressure range from 5 m Torr to 10 Torr. From the lifetime decrease with pressure at low pressure, quenching rate constants were determined, which are equivalent to cross sections in the range of 2.6×10⁻¹⁶ cm². At higher pressures a slow decay was observed that is interpreted as being due to the a′ state which acts as an energy reservoir with a pressure dependent decay constant. We anticipate that laser‐induced fluorescence will be a useful scheme for measuring ground state rotational and vibrational populations for the nitrogen molecule.