Two-dimensional heterodyned and stimulated infrared photon echoes of N-methylacetamide-D

The stimulated infrared photon echo of N-methylacetamide-D [NMAD; ${\mathrm{CH}}_{\mathrm{3}}{\mathrm{(CO)ND(CH}}_3\mathrm{)]}$ was measured and used to determine the vibrational frequency correlation function. The correlation function was modeled as a single exponential plus a constant, and it was found that most of the NMAD vibrational frequency distribution is motionally narrowed with a pure dephasing time of 1.12 ps. The two-dimensional infrared (2D IR) spectrum of NMAD was also obtained by heterodyning the echo field with a weak local oscillator pulse. The real and imaginary portions of the 2D IR spectrum exhibit multiple peaks due to υ=0–1 and 1–2 coherences that are excited, which are not resolved in the absolute magnitude of the 2D IR spectrum. Using the correlation function determined from the stimulated photon echo, the 2D IR spectrum was accurately simulated. Resolution enhancement of the 2D IR spectrum was performed by manipulating the photon echo field with window functions. The enhanced experimental and simulated 2D IR spectra are dramatically narrowed.