  The total photodetachment cross section of a linear triatomic anion is
derived for arbitrary laser polarization direction. The cross section is shown
to be strongly oscillatory when the laser polarization direction is parallel to
the axis of the system; the oscillation amplitude decreases and vanishes as the
angle between the laser polarization and the anion axis increases and becomes
perpendicular to the axis. The average cross section over the orientations of
the triatomic system is also obtained. The cross section of the triatomic anion
is compared with the cross section of a two-center system. We find there are
two oscillation frequencies in the triatomic anion in contrast to only one
oscillation frequency in the two-center case. Closed-orbit theory is used to
explain the oscillations.
