Detection of a new diffuse band around 599.2 nm in single photon excitation of ³⁹K₂ dimer Rydberg states

We report the first observation of bound free emission around 599.2 nm in single photon excitation of ³⁹K₂ Rydberg states using 337.1 nm (N₂) laser radiation from an excimer laser. The broad continuum emission is tentatively assigned to the 2¹Σ⁺_u→X¹Σ ⁺_g transition. The parametric dependences for the new band and the well-known yellow diffuse band (2³Π_g→a³Σ⁺_u), observed around 573.5 nm, have indicated that such emissions are induced by collision energy transfer from high lying Rydberg states. Energy and temperature dependences were also carried out for better understanding of the population mechanism of the upper states, responsible for such emissions.