Vibronic emission from short-lived core-hole states: Theory and applications for the water molecule

Vibronic cross sections for x-ray and Auger decay from short-lived core-hole states in molecules are derived starting from A{}berg's description of atomic x-ray and Auger decay as multichannel-scattering processes [A{}berg, Phys. Scr. 21, 495 (1980)]. The derivation includes a scattering-matrix formulation in which intra- and interchannel interactions as well as nonadiabatic corrections are introduced. Computable expressions for x-ray and Auger vibronic spectra are derived assuming the harmonic approximation for multidimensional nuclear motions. Applications for water are carried out using truly ab initio values for all energy and lifetime-related parameters.