STUDY OF THE IH-OPPENHEIMER SEPARATION BETWEEN LIGHT AND HEAVY NUCLEUS MOTIONS(BR DYNAMICS USING A BORN)

The study of the dynamics of heavy-light + heavy systems using the Bor n-Oppenheimer-type separation between the light and the heavy nuclear motions is presently extended to the IH+Br system. The hydrogenic wave functions that describe the H nucleus motion for clamped I and Br nucl ei, and the potential energy curves that govern the I-Br relative moti on are reported. Particular attention has been paid to the hydrogenic state for which the potential energy curve has a well. Surprisingly, i t is found that this state does not participate in the H-atom exchange process in the reactive collision: IH (upsilon = 0,j) + Br --> I + HB r(upsilon',j'). This reaction mainly proceeds via crossings between di abatic potential energy curves correlated to the IH (upsilon = 0,j) Br and I + HBr(upsilon' = 1, upsilon' = 2,j') limits. In addition, the photodetachment spectrum of the IHBr- anion has been calculated. The present 3D result fairly agrees with the recent calculation of Metz an d Neumark (J. Chem. Phys. 97 (1992) 962). Salient features of the phot odetachment spectrum stem from the hydrogenic wavefunctions properties .