The geometry and infrared absorption spectrum of (RbCs)2 have been studied by full dimensional quantum dynamics simulations. For this purpose, the potential energy and dipole moment surfaces are generated by means of a cluster expansion with all two and three mode correlations, and fitted to analytical expressions with negligible deviations. Accordingly, the ground state (RbCs)2 has a diamond geometry with D(2h) symmetry. The infrared spectrum with frequencies up to 120 cm(-1), exhibits rich details of the fundamentals, overtones, and combination bands; the highest fundamental frequency of (RbCs)2 is only 40.26 cm(-1). The present study unravels important details of the interactions between the widely investigated ultracold RbCs molecules.