A molecular beam apparatus was set up for measuring depletion spectra of single molecules embedded in superfluid helium nanodroplets. Here, we report on the measurement of the rotationally resolved infrared spectrum of the antisymmetric stretching mode of (OCO)-O-16-O-18 in helium nanodroplets ((N) over bar (0) approximate to 2650 atoms). The band origin of (OCO)-O-16-O-18 in helium droplets was found at 2331.770(1) cm(-1) and is therefore shifted by 0.343 cm(-1) to the red compared to the gas phase value [L.S. Rothman, L.D.G. Young, Infrared energy levels and intensities of carbon dioxide - II, J. Quant. Spectrosc. Radiat. Transfer 25 (1981) 505]. The B rotational constant of (OCO)-O-16-O-18 in helium droplets was determined to be 0.1438(5) cm(-1), a value that is by a factor of 2.6 smaller than the known gas phase B constant [L.S. Rothman, L.D.G. Young, Infrared energy levels and intensities of carbon dioxide - II, J. Quant. Spectrosc. Radiat. Transfer 25 (1981) 505]. (c) 2006 Elsevier B.V. All rights reserved.