Two-photon absorption spectroscopy of mass-selected ions: N2O+ and CS+2

Abstract

A technique for the spectroscopic characterization of mass‐selected ions in ground and bound excited electronic states involving two‐photon absorption and fragment ion detection is demonstrated. A triple quadrupole mass analyzer system is used. Collisionally relaxed ions (M⁺) from a high pressure source are mass selected, then excited sequentially by two laser colors (λ₁,λ₂) according to M⁺→^λ₁M⁺*→^λ₂M⁺**→F⁺_i and fragment ions (F⁺_i) are detected. Stable ionic states are characterized by scanning λ₁ with constant λ₂ and this is illustrated on the known transitions of N₂O⁺ (Ã ²Σ⁺←X̃ ²Π) and of CS⁺₂ (B̃ ²Σ⁺_u←X̃ ²Π_g). New spectroscopic information—vibrational frequencies and rotational constants—and dynamic parameters—lifetimes and fragmentation branching ratios—on N₂O⁺(B̃ ²Σ⁺) and CS⁺₂ (C̃ ²Σ⁺_g) are obtained by scanning λ₂ when λ₁ is chosen to populate several or individual rotational levels of the intermediate state.