Time-resolved spectroscopy of the Ar* 2-excimer emission

High-pressure argon was excited by a 2-ns 600-keV e-beam pulse, and time integrated as well as time resolved fluorescence spectra were measured. No significant dependence of line center (126.2±0.1 nm) or spectral width (80±10 nm) of the Ar2 continuum on gas pressure was found in the range 0.5–20 bar. From the buildup time constant of fluorescence we calculated the three-body rate constant for Ar2 formation to be 5×10−33 cm6/sec. The fluorescence decay was found to consist of two exponentials with time constants 8.6 and 39.2 ns at 20 bar and 12.6 and 73.9 ns at 10 bar, respectively. We attribute this behavior to the fluorescence originating from the singlet and triplet upper state. From the spectral shift between the two components we determined the singlet-triplet splitting in the excited Ar2 molecule to be 12 Å corresponding to 760 cm−1.