Obtaining absorptive line shapes in two-dimensional infrared vibrational correlation spectra.

Absorptive line shapes in two-dimensional infrared (2D IR) vibrational spectra are important for an intuitive interpretation of molecular structure and dynamics. We obtain an absorptive 2D IR correlation spectrum by summing complementary spectra from experiments sampling vibrational coherences that oscillate with conjugate frequencies in the initial evolution time period. The 2D correlation spectrum of a coupled vibrational system reveals certain spectral features with tilted line shapes that are explained in terms of unequal contributions of Liouville-space pathways.