The high-resolution infrared spectrum of ((CO2)-C-12-O-18)(2) has been observed in the v(3) band (2314 cm(-1)) region of (CO2)-C-12-O-18 with diode laser absorption spectroscopy of pulsed molecular beam. The vibrational band origin of((CO2)-C-12-O-18)(2) corresponding to the v(3) mode of (CO2)-C-12-O-18 shows a blue shift of 1.62362(19) cm(-1) with respect to that of (CO2)-C-12-O-18. The geometrical parameters of the slipped parallel ground-state structure are R-CC = 3.5947(11) Angstrom and theta(CCO) = 57.97(7)degrees. By calculating vibrational wavefunctions on ab initio potentials for four intermolecular degrees of freedom, the isotope effect on R-CC is found to arise mainly from in-plane tilting. (C) 2004 Elsevier B.V. All rights reserved.