			15min:

ROTATIONAL SPECTRUM OF THE CO₂--CO₂--N₂O TRIMER.

REBECCA A. APPLEMAN, ROBERT L. KUCZKOWSKI, Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055, USA.

The rotational spectrum of a trimer containing CO₂ and N₂O has been assigned using a pulsed supersonic nozzle Fourier transform microwave spectrometer. 43 transitions of the normal species have been fit to a Watson A-reduction Hamiltonian to give the following constants: A = 1597.4630(29) MHz, B = 1232.9673(15) MHz, C = 831.1002(11) MHz, Delta _J = 2.610(33) kHz, Delta _JK = -3.63(14) kHz, Delta _K = 7.30(36) kHz, delta _J = 0.830(15) kHz, and delta _K = 0.71(10) kHz. These constants are consistent with predicted spectra of both CO₂--CO₂--N₂O and CO₂--N₂O--N₂O, but dipole moment data and preliminary isotopic work indicate that the observed spectrum probably belongs to the first species. The structure is believed to be barrel-like, with the three monomer units roughly parallel to each other. Theoretical modeling of the complex, including atom-atom electrostatic, dispersion and repulsion terms, gives minimum energy forms consistent with the observed rotational constants.