Fig. 2: Isolating inhomogeneous contributions to the O-D stretching linewidths.

a Solvent-background subtracted, normalized IR absorption spectra of 5 mol% water in DMF: D₂O (orange) and HOD (green). Isotropic 2D-IR spectra at waiting time T_w = 100 fs of (b) HOD in DMF (10% D₂O in H₂O) and (c) D₂O in DMF. Note that distortions of the 2D-IR lineshape in (b) at \({\widetilde{\nu }}_{{{{\rm{pump}}}}}\approx 2650\) cm⁻¹ presumably result from residual D₂O. Diagonal and anti-diagonal profiles along the lines indicated in the 2D spectra (b, c, colored lines) are displayed for HOD in (d) and for D₂O in (e). Symbols in (d, e) show experimental data and solid lines show fits (for details, see Supplementary Note 2). Dotted line represents \({\Delta \alpha}=0\). Note that the linewidths of the diagonal signals in (d, e) differ from the widths in (a) due to the different experimental sensitivities to the transition dipole²⁸.