The (2+1) multiphoton ionization spectrum of jet-cooled CS2 between 54 000 and 58 000 cm−1

The (2+1) multiphoton ionization (MPI) spectrum of jet-cooled CS2 has been recorded in the range 345–370 nm, corresponding to a two-photon frequency between 54 000 and 58 000 cm−1. The origin bands of the ...2π3g4sσg 1Πg and 3Πg←X̃ 1Σ+g Rydberg transitions have been observed at 351.04 and 355.15 nm (vacuum 56 974 and 56 315 cm−1), respectively. A third, broader and stronger, band is observed at ∼365 nm corresponding to a two-photon transition at ∼54 700 cm−1, which is suggested to belong to the valence 5σu3πu 1Πg state. The position of the two-photon band at 351 nm establishes it as the one-photon electric-dipole forbidden origin of the 800 cm−1 progression observed in the ultraviolet absorption spectrum. The first-photon frequency of this transition falls at a level corresponding to the ã 3A2 valence state, so that the (2+1) MPI spectrum is supplemented by numerous transitions associated with the (1+2) MPI spectrum of the 3A2←X̃ 1Σ+g transition.