This project is concerned with solvent effects on the structural properties of nitrogen-donor-SO2 complexes, including: H3N-SO2, and its methylated (CH3 containing) analogues. The goal is to assess the extent to which inert, condensed-phase environments (solid neon, argon, and nitrogen) induce structural change in these systems. Experimentally, we utilize infrared spectroscopy to observe shifts in key vibrational modes that parallel the compression of the N-S bond. Theoretically, we use quantum-chemical calculations (computer simulations of the bonding) to predict gas-phase structural properties, bond energies, vibrational frequencies as well as the energy profile along the N-S bond. Our preliminary computational results indicate that these complexes will undergo significant structural changes. A great deal of effort went into identifying the optimal computational methods to make this determination. The first consideration was identifying which among twelve methods tested best predicated the experimental frequencies of SO2, and using this method, we will report gas-phase and structures and predicted frequencies for H3N-SO2, CH3H2N-SO2, (CH3)2HN-SO2 and (CH3)3N-SO2. Collectively these complexes span a great range of interaction strengths, specifically: H3N-SO2: –6.6 kcal/mol (RNS=2.685 Å), CH3H2N-SO2: -8.4 kcal/mol (RNS=2.509 Å), (CH3)2H2N-SO2: -11.0 kcal/mol (RNS=2.334 Å), (CH3)3H2N-SO2: -13.4 kcal/mol (RNS=2.302 Å). We also explored the performance of various computational methods for energetic results by comparing them to a very high-level model and also compared predicted frequencies to those previously measured in solid nitrogen.
