The infrared spectrum and structure of the nitrous oxide trimer

Reported here are the first spectroscopic observations of the nitrous oxide trimer. Two rotationally resolved vibrational bands have been observed using the optothermal detection method. The ground vibrational state rotational constants obtained from these spectra are A=0.052 606(40), B=0.043 571(15), and C=0.028 736(7) cm−1. Ab initio calculations are also reported here, at the MP2/6-31+G(2d,2p) level, which yield A=0.054 92, B=0.045 17, and C=0.030 52 cm−1. The structure of the nitrous oxide trimer can be thought of as a slightly distorted dimer, which has a slipped parallel geometry [Z. S. Huang and R. E. Miller, J. Chem. Phys. 89, 5408 (1988)], with a third monomer unit lying above this dimer. This structure is similar to the recently observed nonplanar isomer of (CO2)3 [M. J. Weida and D. J. Nesbitt, J. Chem. Phys. 105, 10,210 (1996)].