Distinguishing Population and Coherence Transfer Pathways in a Metal Dicarbonyl Complex Using Pulse-Shaped Two-Dimensional Infrared Spectroscopy

Abstract

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 create intensity oscillations and add 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.

Ultrafast Coherence Delocalization in Real Space Simulated by Polaritons

“…Because the four polariton states could generate many pathways that contributed to 2D IR signals when broadband pulses were used, to avoid unnecessary signals and focus on coherence delocalization only, we applied tailored pulse sequences to create specific coherences. [ 34,45,46 ] For example, we truncated the first two pulses in the frequency domain so that it only created the initial coherence |UP i 〉〈LP i |, where i represented cavity A or B. Then, we scanned t 2 (the time delay between the second pump pulse and probe pulse, Figure 1a) to monitor the coherence evolution.…”

Excited-State Vibration-Polariton Transitions and Dynamics in Nitroprusside

“…Selective pumping is an established technique 24,49,50 which we implement in the 2D IR apparatus via a pulse shaper. The pulse shaper disperses the pump beam in frequency across the AOM.…”

“…For the following results, we chose to obtain pump-probe data at a series of waiting times rather than collecting full 2D IR spectra, which reduced data collection time by two orders of magnitude while still preserving comparable signal-to-noise ratios. We maintain state-selective excitation by using spectrally filtered pump pulses, which has been used before to suppress oscillations in 2D IR measurments 24,49,50 . The spectrally filtered pulses are created with the mid-IR pulse shaper, which allows us to impose an arbitrary frequency mask on the pump pulse.…”

Recent advances in multidimensional ultrafast spectroscopy

“…The data are subsequently windowed, apodized and Fourier-transformed along the t 1 axis to generate a 2D ω 1 -ω 3 correlation map, for a specific value of the waiting time. Depending on the vertical Franck-Condon factors between the |g and |e states, and the laser bandwidth used, electronic, vibronic or vibrational coherences will be launched and propagated, leading to oscillations in the corresponding 2D spectra as a function of the waiting time [1,3,9,23,[70][71][72][73].…”