Collapse of Vibrational Structure in the Auger Resonant Raman Spectrum of CO by Frequency Detuning

Observations made in the $\mathrm{C}1s\to {\pi }^{*}$ Auger resonant Raman spectra of carbon monoxide demonstrate that the vibrational structure in such spectra is strongly frequency dependent. In the limit of narrow bandpass photon excitation, the vibrational excitations of the $5\sigma$ participator transition collapse to one single line within a sub-eV detuning range. The effect is explained in terms of a generalized duration time for the resonance process, in which the lifetime of the core excited state and the inverse of the detuning frequency play equal roles.