Time-resolved emission spectroscopy in laser-generated nitrogen plasmas

Extremely high-lying states of atomic and molecular nitrogen ions have been observed and analyzed in the transient plasma that results from focusing a Q-switched Nd:YAG (where YAG denotes yttrium aluminum garnet) laser into a pure nitrogen atmosphere ranging in pressure from 100 to 800 Torr. During the first 10 to 80 ns after plasma ignition several states of N³⁺ can be detected. Their Stark broadened linewidth is strongly time dependent due to the rapidly changing electron density in the decaying plasma. At around 20 to 40 μs after plasma ignition, rotationally resolved emission in the first negative system of N₂⁺, ²Σ_u⁺→X ²Σ_g⁺ indicates a rotational and vibrational temperature of about 9500 K. No significant interference from the second positive system C ³Π_u→B ³Π_g of the neutral molecule is observed. Under these conditions rotational levels up to N’=112 in the R branch of the (0,0) band have been identified. In this band, new perturbations at around N’=82 and 95 due to the v=12 and 13 vibrational levels of the A ²Π_u state are reported.