Renner–Teller effect and Rydberg-valence mixing in the N and O K-edge photoabsorption spectra of N2O

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Abstract
We have measured high-resolution angle-resolved ion-yield spectra of the O and N 1s excited N2O molecules (Nt–Nc–O) and investigated them with the help of ab initio quantum chemical calculations. The peak width of the Nc 1s→π* transition is larger than that of the Nt 1s→π* one. This mainly arises from different populations of bending vibrations excited through the Renner–Teller effect, which breaks the degeneracy of the 1s→π* excited states by bending the linear molecule. The angular distribution of fragment ions emitted after the Auger decay is also affected by the Renner–Teller effect. That is, fragment ions significantly lose the information of the Π symmetry of the linear molecule. For the 1s→Rydberg excitations no Renner–Teller effect is observed and the angular distribution is directly related to the Σ and Π symmetries. Furthermore, it is found that the peak intensities of the O and Nt 1s→nsσ Rydberg transitions are unusually large. The N2O molecule has two σ* orbitals, σs*(8σ) and σp*(9σ), below and above the ionization threshold and the 1s→σs* excited states are mixed with the O and Nt 1s–nsσ Rydberg excited states; on the other hand, the Nc 1s→σs* transition is almost dipole-forbidden because of the orbital symmetry.