evolution of the vibrational coherence in t 2 (i.e., the delay time, s 1 ). Most notably,
vibrational resonances of triiodide and diiodide appear in separate dimensions of the
2DRR spectrum in terms 9–12; this is the pathway defined in Fig. 1.
In previous work [22, 23], response functions were written under the assumption
that the laser pulses are short compared to the vibrational period but long compared
to electronic dephasing (i.e., the snapshot limit) [23]. Both approximations are
appropriate for the experiments we have conducted on triiodide. In these limits, the
components of the fifth-order polarization consist of products of Lorentzian
functions. Fourier transformation with respect to the experimentally controlled
delay times, s 1 and s 2 , yields a 2D spectrum in the conjugate dimensions, x 1 and x 2 .
Fig. 4 Energy level representations associated with individual pathways in a term 1, b term 5, and c term
9. It is assumed that the chemical reaction is fast compared to the vibrational periods of the reactants and
products. Solid and dashed arrows correspond to field-matter interactions with the ket and bra in the
Feynman diagrams presented in Fig. 3
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