Distinguishing Population and Coherence Transfer Pathways in a Metal Dicarbonyl Complex Using Pulse-Shaped 2DIR Spectroscopy

Collection of two dimensional infrared (2DIR) spectra using two ultrafast, broadband infrared pump pulses followed by an ultrafast probe pulse optimizes the experimental time and frequency resolution, but can also introduce quantum beat and coherence transfer pathways. The associated coherent dynamics can introduce intensity oscillations and extra features to 2DIR spectra. We describe a method to suppress these pathways using pump-pulse shaping, without significantly degrading the time and spectral resolution. We illustrate the method for a rhodium dicarbonyl complex, acetylacetonato dicarbonyl rhodium, to establish the relative importance of coherence and population transfer between carbonyl symmetric and asymmetric stretching modes. Our technique effectively suppresses the quantum beats. Comparison of peak intensities obtained with shaped and unshaped pump pulses demonstrates that coherence transfer does not play a significant role in the 2DIR spectrum of RDC in this spectral region.