Rate equation modelling of molecular multiphoton ionization dynamics

Selected aspects of kinetic rate equations are used as a framework for the modelling of molecular multiphoton ionization. Expressions are obtained for the ion yield where one and two intermediate resonances are present and the effects of saturation due to laser beam spatial and temporal structure are shown to be important in many molecular multiphoton experiments. A comparison is made between ionization and fluorescence yields and their spatial structure, following two-photon excitation, under identical experimental conditions. Radiationless processes are shown to be important in determining the ionization yield, which leads to the apparent selectivity of molecular multiphoton ionization experiments toward Rydberg states.