Multiphoton absorption line shapes and branching ratios in intense laser fields: An application toH2+photodissociation

Time-dependent transition amplitudes between bound and continuum states coupled by an intense laser field are expressed in terms of their energy-dependent analogs maintaining the coherence effects through the intervention of complex molecular dressed states (field-induced resonances). A coupled-equation method combined with an artificial-channel technique, properly describing the preparation step, is used to calculate absorption line shapes and branching ratios of the Floquet states involved in the multiphoton absorption-emission processes. The formalism is applied to the photodissociation of ${\mathrm{H}}_2^{+}$(1s${\mathrm{\sigma }}_{\mathit{g}}$,v=0,j=1→2p${\mathrm{\sigma }}_{\mathit{u}}$). The intense-field behavior of laser-induced resonance Fano profiles are analyzed in relation with the dissociation line shapes. Strong mixings appear for intensities larger than ${10}^{13}$ W/${\mathrm{cm}}^2$ and the distribution of higher-energy peaks decreases with increasing intensity, due to stimulated emissions of the dissociating fragments.