title: Ab initio study of the Br(2P)-HBr van der Waals complex.
abstract: This study reports an ab initio characterization of a prereactive van der Waals complex between an open-shell atom Br((2)P) and a closed shell molecule HBr. The three adiabatic potential surfaces 1 (2)A('), 2 (2)A('), and 1 (2)A("), which result from the splitting of degenerate P state of Br are obtained from coupled cluster calculations. The coupling between same-symmetry states is calculated by multireference configuration-interaction method. A transformation to a diabatic representation and inclusion of the spin-orbit coupling effects on the interactions are also discussed. Bound states are calculated using an adiabatic bender model. The global minimum on the lowest adiabatic potential surface corresponds to a T-shaped geometry and has a well depth of D(e)=762.5 cm(-1) at R(e)=3.22 A. A secondary minimum occurs for a hydrogen-bonded geometry with D(e)=445.3 cm(-1) at R(e)=4.24 A. Upon inclusion of spin-orbit coupling the hydrogen-bonded minimum remains at the same depth, but the T-shaped minimum washes out to less than half of its spin-free value. The lowest bound state is localized in the linear minimum. The spin-orbit coupling plays a very important role in shaping of the potential energy surfaces of Br-HBr.
authors.affiliation: Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland.
authors.forename: R
authors.initials: R
authors.lastname: Toboła
authors.forename: G
authors.initials: G
authors.lastname: Chałasiński
authors.forename: J
authors.initials: J
authors.lastname: Kłos
authors.forename: M M
authors.initials: MM
authors.lastname: Szcześniak