V. CONCLUSIONS detached-electron wave from center 1 with the source at center 0 and the source at 2 produce the sin( kd ) and sin(2 kd ) oscillations in the total cross section. Detached-electron wave from center 2 also have similar interference terms. The final oscillation amplitudes include all the interference terms. We will not repeat the detail of such derivation which is quite similar to the two-center case[36]. We emphasize that such a derivation based on closed-orbit theory establishes that kd is the action ∫ $^{p}$· d q of the detached-electron propagating from one cen- ter to a neighboring center and 2 kd is the action of the detached-electron propagating from center 1 to center 2 or from center 2 to center 1. The two oscillations are directly associated with the detached-electron orbits from one center to a neighboring center having action kd and the detached-electron orbits connecting center 1 and 2 having action 2 kd . We have studied the photodetachment of the recent triatomic anion model[38] in the general case. We have derived the total photodetachment cross section for arbitrary laser polarization direction. It is demonstrated there are two oscillation frequencies in the cross sections. The amplitudes of the oscillations can be varied by changing the laser polarization direction. The amplitudes are largest when the laser polarization is parallel to the anion axis. As the laser polarization direction is turned to be perpendicular to the axis, the oscillation amplitudes decrease and vanish. We also obtained the average cross section for random orientations of anion. The averaging procedure modifies the oscillation amplitudes but it does not change the oscillation frequencies. The two oscillations in the present three-center system can be explained using closed-orbit theory as interference between detached-electron waves produced from one center and the sources at other centers. Two types of detached- electron orbits are responsible for the two oscillations. 8 [1] H. C. Bryant et al ., Phys. Rev. Lett. 58 , 2412 (1987). [2] J. E. Stewart et al ., Phys. Rev. A 38 , 5628 (1988). [3] M. L. Du and J. B. Delos, Phys. Rev. A 38 , 5609 (1988). [4] M. L. Du and J. B. Delos, Phys. Lett. A 134 , 476 (1989). [5] M. L. Du, Phys. Rev. A 40 , 4983 (1989).