Vibrationally resolved O1score-excitation spectra of CO and NO

Abstract

High-resolution photoabsorption spectra of CO and NO below the O $1s$ ionization threshold are presented. The vibrational fine structure of the O $1\stackrel{\ensuremath{\rightarrow}}{s}{\ensuremath{\pi}}^{*}$ and O ${1s}^{\ensuremath{-}1}$ Rydberg excitations could be resolved for both molecules, allowing a determination of the vibrational energies and intramolecular distances of the core-excitation states in CO and NO from Franck-Condon analyses. Ab initio calculations are performed for the O $1\stackrel{\ensuremath{\rightarrow}}{s}{\ensuremath{\pi}}^{*}$ excitation in CO to give an independent confirmation of the spectroscopic parameters derived from the Franck-Condon analysis. The spectral features of the O ${1s}^{\ensuremath{-}1}$ Rydberg region in CO are reassigned on the basis of the experimental results. The results obtained for the O ${1s}^{\ensuremath{-}1}3s$ Rydberg state in NO support the idea of a weakening of the molecular bond upon an O ${1s}^{\ensuremath{-}1}$ ionization process.