Nonlinear two-dimensional vibrational spectroscopy

There is currently great interest in developing the vibrational analog to t wo-dimensional NMR spectroscopy. One approach to implementing two-dimension al vibrational spectroscopy is to use doubly vibrationally enhanced (DOVE) four-wave mixing (FWM). Nonlinear signals occur because of correlations and mode coupling that are induced by interactions involving the driven modes. Since cross peaks do not occur between modes if interactions are absent, s pectral congestion is removed and only the coupled modes remain. We describ e the development of a two-dimensional doubly vibrationally enhanced four w ave mixing method that extends the doubly resonant nonlinear spectroscopies to vibrational nonlinearities. We demonstrate the selective enhancements o f coupled modes that are possible with the double resonances where the inte nsity of the enhancements reflects the strength of the interactions that ar e responsible for the vibrational mode coupling. We also demonstrate the ca pabilities for selectively enhancing specific sample components in an isoto pic mixture. Since biological applications of DOVE require aqueous environm ents, we have examined the ability of DOVE methods to discriminate against the strong water absorption and have found that water has a small vibration al nonlinearity that allows DOVE of the solutes. Our results demonstrate th e feasibility and features required to make DOVE methods practical for a wi de range of scientific applications where identification of intra- and inte rmolecular interactions is important.