THE COMPLEX H3N-CENTER-DOT-CENTER-DOT-CENTER-DOT-BR-2 CHARACTERIZED IN THE GAS-PHASE BY ROTATIONAL SPECTROSCOPY

The ground-state rotational spectra of four isotopomers of the complex H3N...Br-2 have been observed using pulsed-nozzle, FT microwave spectroscopy. Reaction of NH and Br-2 was avoided by using a fast-mixing nozzle. The isotopomers (H3N)-N-15...Br-79(2),(H3N)-N-15...(BrBr)-Br-81-Br-79,(H3N)-N-15...(BrBr)-Br-79-Br-81, 3 and (H3N)-N-15...Br-81(2) exhibited symmetric-top type spectra which were analyzed to give rotational constants B-0, the centrifugal distortional constants D-J and D-JK, the Br-nuclear quadrupole coupling constants (chi)(Br-x) (x=i, inner or o, outer), and the Br spin-rotational coupling constants M(bb) (Br-x). The distances r(N...Br-i)=2.72(2) Angstrom and r(Br-Br)=2.335(10) Angstrom in the complex were estimated from the rotational constants while the intermolecular stretching force constant k(sigma)=18.5(5) N m(-1) was determined from D-J. An interpretation of the magnitude of the (chi)(Br,) values and the difference Delta(chi)(Br)=(chi)(Br-i)-(chi)(Br-o) allows the conclusion that the extent of intermolecular charge transfer is probably small and that a polarization of Br-2, equivalent to the transfer of similar to 0. le from Br-i to Br, accompanies formation of the complex. The properties of the series of complexes H3N...XY, where XY=Cl-2, BrCl, and Br-2 are compared. (C) 1995 American Institute of Physics.