posted on 2006-12-21, 00:00authored byErik R. Berg, Sarah A. Freeman, Daniel D. Green, Darin J. Ulness
The effects of hydrogen bonding on the ring stretching modes (both ring breathing and triangle) of pyridine
are experimentally investigated using noisy light based coherent Raman scattering spectroscopy. Three systems,
pyridine/formamide, pyridine/water, and pyridine/acetic acid, provide varying degrees of strength for the
diluent−pyridine hydrogen bond complex. Formamide forms a relatively weaker hydrogen bond, while acetic
acid essentially fully transfers a proton to pyridine. Both dilution studies and temperature studies are performed
on the three systems. Together, these provide a broad context in which a very simple model for the electronic
behavior of pyridine is formulated. This model is based on a molecular orbital picture and electrostatic
arguments, and it well explains the observed experimental results. Additionally, a new mechanism for the
line broadening of the ring breathing mode for the pyridine−water hydrogen bonded complex is proposed.