Knowledge Bank

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 $estimateh$. These measurements follow our previously $reportedi$ 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.