Spectroscopy of the R-system (1 8 0) group band of CS2 achieved by Λ-type excitation

We have demonstrated a high resolution spectroscopic technique, the so-called Λ-type excitation, to re-investigate (1 8 0) group band of CS2, which is closely located below the barrier of bent to linear. Λ-type excitation is a three-photon process. Rotationally resolved spectroscopy can be achieved as long as the chosen intermediate state can be rotationally resolved. Applying this technique, we are able to resolve the doublet due to the complexity of the potential near the bent-to-linear barrier top. And due to gaining a favorable Frank-Condor factor from the initial state (3 18 0), instead of (0 0 0), a combination mode having 2ν3 excitation induced by ν2 mode Coriolis interaction was observed as well.