15min:

M. REZAEI, J. NOROOZ OLIAEE, N. MOAZZEN-AHMADI, Department of Physics and Astronomy, University of Calgary, 2500 University Dr., N.W., Calgary, AB T2N 1N4, Canada; A. R. W. MCKELLAR, Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, ON K1A 0R6, Canada.

High resolution spectra have previously been studied for N₂O dimers (two isomers), trimers (one isomer), and tetramers (two isomers). Here, we assign two new bands to the N₂O pentamer. The bands are observed in the region of the N₂O ₁ fundamental using a tunable laser to probe a pulsed supersonic slit jet expansion. They are centered at 2233.9 and 2236.4 cm^-1 for ¹⁴N₂O, and at 2164.4 and 2166.8 cm^-1 for ¹⁵N₂O. Attribution to the pentamer is based on comparison of the observed rotational constants with theoretical ones from calculated cluster structures based on two rather different N₂O pair potentials. The first potential function is from a recent high level ab initio study. The second potential is a relatively simple empirical one, based partly on fitting to bulk properties. The likely pentamer structure is a completely unsymmetric one. It can be visualized starting with a highly symmetric oblate tetramer which is attacked by a fifth monomer, locating itself at a favorable distance and breaking the symmetry. Interestingly, analysis of the two bands yields very similar but not quite identical ground state parameters. We believe that they are due to distinct isomers having this same basic structure but differing in the orientation direction of one N₂O monomer.