A study of some Rydberg states of CO2 by (3+1) multiphoton ionization spectroscopy

The MPI spectra of CO2 were recorded in the range 275 to 338 nm in both a conventional MPI cell and a molecular beam apparatus. The polarization ratio of each MPI peak was measured in order to assign the symmetry of excited states. The 3pσu1Πu and 3pσu1Πu110 Rydberg states were observed, while the 3pπu1Σ+u Rydberg state was missing, and a new Rydberg state, 3pπu1Δu was observed at 333.03 and 333.70 nm. In the nf (n=4,5) Rydberg series, evidence was found of interaction with other nearby Rydberg states. A mass selected pure CO+2 ion signal was measured for the 3pπu1Δu state, but both CO+ and CO+2 ion signals were detected for the other Rydberg states. Predissociation and fragmentation in MPI processes are discussed. Lower limit lifetimes for the observed Rydberg states of CO2 are given