Molecular dynamics in intense laser fields

We discuss recent developments in the study of the interaction of intense l asers with diatomic molecules. An overview of theory and experiment is give n and particular attention is given to the energy spectra of ions resulting from photodissociative ionization. The ionization process is studied in th e multiphoton regime using Floquet theory and compared with field-ionizatio n results appropriate for the tunnelling regime. A review is given of the e vidence for the existence of critical distances between the nuclei at which ionization rates are strongly enhanced. The field-ionization model is foun d to reproduce the main features observed by experiments. The field-ionizat ion Coulomb explosion (FICE) model accurately reproduces the kinetic energy releases and threshold intensities of the various fragmentation channels o f the iodine dimer: I-2. With the three-dimensional FICE model, threshold i ntensities as a function of angle between the molecular axis and the laser E-field are calculated. The angular distributions obtained are in good agre ement with measurements taken for distributions of I-2 fragments. The angul ar distributions of the H-2 and N-2 fragments, on the other hand, are much more sharply peaked, indicating reorientation by the laser field.