High-resolution x-ray spectra of carbon monoxide reveal ultrafast dynamics induced by long UV pulse
In theoretical simulations of a UV + x-ray pump-probe (UVX-PP) setup, we show that frequency detuning of the pump UV pulse acts as a camera shutter by regulating the duration of the UVX-PP process. This two-photon absorption with long overlapping UV and x-ray pulses, allowing for high spectral resolution, thereby provides information about ultrafast dynamics of the nuclear wave packet without the requirement of ultrashort pulses and controlled delay times.
In a case study of carbon monoxide, the calculated UVX-PP spectra of the O1s−12π1 and C1s−12π1 core-excited states show different vibrational profiles. The interference of intermediate vibrational states reveals details of nuclear dynamics in the UVX-PP process related to a variable duration time controlled by the UV detuning. Both O1s−12π1 and C1s−12π1 pump-probe channels display a splitting of the spectral profile, which however is associated with different physical mechanisms. At the O1s−12π1 resonance, the observed dispersive and non-dispersive spectral bands intersect and result in destructive interference.