THE PERPENDICULAR NU(4)(- +1)+NU(6)(-/+1) COMPONENT OF THE ROVIBRATIONAL NU(4)+NU(6) BAND OF (CH3BR)-BR-79, STUDIED IN A HIGH-RESOLUTION FTIR SPECTRUM FROM 3870CM(-1) TO 4110CM(-1)/

860 rotational lines of the almost unperturbed nu4(-/+1) + nu6(-/+1) c omponent of the nu4 + nu6 band of CH3 Br-79 have been assigned in spit e of overlaps with several other bands. Only a few sub-bands (KDELTAK = 1, -7, -8, -9) are subject to slight resonances. An RMS deviation of 0.0039 cm-1 has been achieved by a least-squares fit of 742 lines. As expected, the A', B', D(J)', D(JK)' and D(K)' molecular constants hav e been found quite close to those of the parallel component. The compa rison between the centres of both components of the nu4 + nu6 band all owed us to measure two anharmonicity constants: x46 = -5.25 cm-1 and g 46 = 0.89 cm-1.