  In this paper we report the theoretical results obtained for partial
ionization yields and the above-threshold ionization (ATI) spectra of Magnesium
in a Ti:sapphire laser field (804 nm) in the range of short pulse duration
(20-120 fs). Ionization yield, with linearly polarized light for a 120 fs laser
pulse, is obtained as a function of the peak intensity motivated by recent
experimental data \cite{gillen:2001}. For this, we have solved the
time-dependent Schr\"{o}dinger equation nonperturbatively on a basis of
discretized states obtained with two different methods; one with the
two-electron wavefunction relaxed at the boundaries, giving a quadratic
discretized basis and the other with the two-electron wavefunction expanded in
terms of Mg$^+$-orbitals plus one free electron allowing the handling of
multiple continua (open channels). Results, obtained with the two methods, are
compared and advantages and disadvantages of the open-channel method are
discussed.
