INTENSE FIELD-IONIZATION OF MOLECULES WITH ULTRA-SHORT LASER PULSES-ENHANCED IONIZATION AND BARRIER-SUPPRESSION EFFECTS

Exact numerical solutions of the time-dependent Schrodinger equation h ave been performed in order to calculate ionization rates in intense ( I greater than or equal to 10(14) W cm(-2)) short (t < 100 fs) laser p ulses for linear three-dimensional H-3(2+) and linear one-dimensional H-4(3+), H-4(2+). All molecular ions exhibit unusually large ionizatio n rates at large critical interfragment distances R-c similar or equal to 5 au. Expressions are derived for R-c based on quasistatic models of field-induced suppression of electron Coulomb barriers in the molec ules. The predicted R-c agree satisfactorily with the exact numerical results. In the symmetric case, laser-induced electron localization ca n also enhance ionization. The present numerical results show that lar ge or enhanced ionization rates exceeding those of nonionized fragment s will dominate for laser pulses which are sufficiently long to allow dissociative ionization fragments to reach such critical distances.