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DETERMINATION OF THE DIPOLE MOMENT OF H₃N-SO₃.

MANJULA CANAGARATNA, M. E. OTT AND K. R. LEOPOLD, Department of Chemistry, University of Minnesota, 207 Pleasant St., SE, Minneapolis, MN 55455.

The dipole moment of H₃N-SO₃ has been determined using pulsed nozzle Fourier transform microwave spectroscopy. The value obtained, 6.204(12) D, is in reasonable agreement with published ab initio estimates . These measurements follow our previously reported structural work on this complex in which the intermolecular N-S bond was shown to be significantly longer in the gas phase than in the solid state. Presumably, the mechanism for the contraction of the N-S bond upon crystallization involves a sharply rising dipole moment function at shorter distances. Thus, the present result is especially interesting in connection with the observed gas-solid structure changes. The complex has also been postulated as a potential seed molecule for the nucleation of atmospheric aerosols, and we comment on possible implications of its phase-dependent structure and bonding on the kinetics and thermodynamics of the nucleation process.