THE ROTATIONAL SPECTRUM OF THE BENZENE HYDROGEN BROMIDE COMPLEX

Ground-state rotational spectra of six symmetric-top isotopomers, C6H6 ... (HBr)-Br-79, C6H6 ... (HBr)-Br-81, C6D6 ... (HBr)-Br-79, C6D6 ... (HBr)-Br-81, C6H6 ... (DBr)-Br-79 and C6H6 ... (DBr)-Br-81, of the be nzene-hydrogen bromide complex were observed and analysed to give the rotational constant B-0, the centrifugal distortion constants D-J and D-JK, and the Br nuclear quadrupole and spin-rotation coupling constan ts chi(aa) and M-bb in each case. It is concluded that in the zero-poi nt state the complex has effective C-6v symmetry, with HBr oriented so that H lies closest to the benzene ring and undergoes a circular moti on which allows it to sample the pi-electron density of the ring. (C) 1997 Elsevier Science B.V.