Interference effects in Auger resonant Raman spectra of CO via selective vibrational excitations across the O $1s\to 2\pi$ resonance

The Auger resonant Raman spectra of CO, arising from the transitions to the $X$ and $A$ final electronic states of $\mathrm{C}{\mathrm{O}}^{+}$, have been recorded at photon energies corresponding to the vibrational excitations $v^{\prime }=3,5$, and 8 in the O $1s\to 2\pi$ resonance. The spectra are simulated within the model that takes into account both the lifetime-vibrational interference (LVI) and interference with the nonresonant photoemission. The spectroscopic parameters, ${\omega }_e$, ${\omega }_e{x}_e$, $\Gamma$ and $r_e$, of the O $1s^{-1}2\pi$ core-excited state, necessary for the simulation, have been derived by fitting the Franck-Condon simulation to the total ion yield spectrum, assuming a Morse potential for the O $1s^{-1}2\pi$ state. Not only the LVI but also the interference with the nonresonant photoemission turn out to be significant.

Figure 1

(Color online) The O $1s\to 2\pi$ total ion yield spectrum of CO. The solid line represents the best fit to the experimental data points (open circles).

Figure 2

Measured electron emission spectra from the two outermost valence orbitals at three different excitation energies corresponding to excitations to the $v^{\prime }=3$, 5, and 8 vibrational components of the O $1s^{-1}2\pi$ core-excited state (resonant spectra) and at an energy of $530.92\mathrm{eV}$, i.e., below the resonance (“nonresonant” spectrum).

Figure 3

(Color online) Upper panel: The measured (circles) and simulated (solid line) electron emission spectra via excitation to $v^{\prime }=3$ of the O $1s^{-1}2\pi$ core-excited state. The simulation includes only the LVI. The presented experimental spectra are the difference between the resonant and “nonresonant” spectra. See text for the details. Lower panel: direct (solid blue line) and interference (dotted green line) terms defined by Eq. (2).

Figure 4

(Color online) The measured (circles) and simulated (solid line) electron emission spectra via excitation to $v^{\prime }=5$ of the O $1s^{-1}2\pi$ core-excited state. See the caption of Fig. 3 and text for the details.

Figure 5

(Color online) The measured (circles) and simulated (solid line) electron emission spectra via excitation to $v^{\prime }=8$ of the O $1s^{-1}2\pi$ core-excited state. See the caption of Fig. 3 and text for the details.

Figure 6

(Color online) Upper panel: The measured (circles) and simulated (solid red line) spectra via excitation to $v^{\prime }=3$ of the O $1s^{-1}2\pi$ core-excited state. The simulation includes both the LVI and the interference with the direct photoionization channel. The experimental spectrum is the same as the resonant spectrum in Fig. 2. See text for the details. Lower panel: LVI (solid blue line), direct photoionization (thin dotted red line) and interference (dotted green line) terms defined by Eq. (4).

Figure 7

(Color online) The measured (circles) and simulated (solid red line) spectra via excitation to $v^{\prime }=5$ of the O $1s^{-1}2\pi$ core-excited state. See the caption of Fig. 6 and text for the details.

Figure 8

(Color online) The measured (circles) and simulated (solid red line) spectra via excitation to $v^{\prime }=8$ of the O $1s^{-1}2\pi$ core-excited state. See the caption of Fig. 6 and text for the details.