A transient pump-probe spectrum was collected at a waiting time of 150 fs and used in phasing the heterodyned fast-scan BoxCARS 2D IR spectra (Figure ). Example rephasing, nonrephasing, and absorptive spectra collected with the four-frame phase cycling scheme at a waiting time of 150 fs are included in Figure . Additionally, to demonstrate the capabilities of this new optical setup for fast measurement of weak vibrational probes, 2D IR spectra of 50 mM sodium thiocyanate (NaSCN) (≥98.0%; Sigma-Aldrich) in D2O (99.9%; Cambridge Isotope Laboratories, Inc.) were collected at a waiting time of 150 fs with the same aforementioned experimental parameters. The absorbance of the nitrile stretching mode at 2067 cm -1 was measured to be 0.1 OD in the sample used for 2D IR