ABOVE-THRESHOLD IONIZATION ELECTRON-SPECTRA FROM A DISSOCIATING MOLECULAR ION CALCULATED USING THE WAVE-FUNCTION SPLITTING TECHNIQUE

Above-Threshold Ionization (ATI) electron kinetic energy spectra from a H-2(+) molecule were calculated numerically by solving the time-depe ndent Schrodinger equation and were compared with the spectra generate d by a hydrogen atom. We observe that the ionizing electron at one pro ton can gain additional energy due to scattering on its neighbor (abso rption of photons via inverse bremsstrahlung). This leads to the enhan cement of a plateau appearing above the energy 10U(p), where U-p is th e ponderomotive energy. For very large internuclear distances, this pl ateau extends up to 20U(p). Strong dependence of shapes of ATI spectra on the internuclear distance is found. The presence of very high ener gy photoelectrons necessitates the use of extremely large ,grids in nu merical simulations based on the full time-dependent Schrodinger equat ion. We present a wave-function splitting scheme, which allows one to circumvent the problem of large grids and thus obtain accurate multiph oton photoelectron spectra. The technique relies on splitting the inte gration grid into two overlapping regions, one close to nuclei and the other one far from nuclei.