Femtosecond dissociation of core-excited HCl monitored by frequency detuning

Core excitation of gaseous HCl to the dissociative sigma* state leads to a deexcitation spectrum with two qualitatively different contributions-a broad molecular background and narrow atomic lines. The experiment demonstrates that the ratio of integrated intensities from these two contributions depends crucially on the excitation frequency; the molecular background is enhanced with increased detuning of the photon frequency. This is discussed in a time-dependent model, using the concept of an effective duration time for the resonant x-ray scattering process. [S0031-9007(97)04296-8].