Abstract:

On the basis of population rate equation of multiphoton ionization and fragmentation processes, the controllability of fragmentation process in MPI experiments of polyatomic molecules is analyzed in this paper. Curves of ionization efficiency and mean energy < E > of ions versus laser intensity were calculated for different ionization schemes. From the calculation results, we find that only 1+1 ionization scheme, soft ionization and hard fragmentation can be controlled by changing the intensity of ionization laser. For 3+1 ionization scheme , duo to additional absorption photons after ionization, the ions have already obtained internal energy far exceeds the dissociation threshold of the parent ion, so the parent ion formed by ionization can completely dissociate to daughters in the same laser pules. Our analysis can explain why parent ions didn’t appear in MPI mass spectra of furan molecule at 450nm.  

Key words: Population rate equation, Multiphoton ionization, Mass spectrum, Fragmentation, Furan