Table 2.

Cross-peak data from 2D IR spectra

Sample	ωexc,1	ωdet,1	I1	ωexc,2	ωdet,2	I2
apo	1,593	1,633	0.30	1,613	1,642	0.31
Ca2+	1,597	1,637	0.44	1,614	1,641	0.64
La3+	1,596	1,633	0.22	1,613	1,644	0.20
Tb3+	1,597	1,633	0.26	1,613	1,643	0.28

Each spectrum contains two cross-peaks, the lower-frequency of which is subscripted “1” and the higher-frequency of which is subscripted “2”. Parameters included for each pair of cross-peaks: I, the normalized peak intensity of the cross-peak relative to the strongest feature in the spectrum; ω_det, the detection frequency at which the peaks appear (cm⁻¹); ω_exc, the excitation frequency at which the cross-peak appears (cm⁻¹). No cross-peaks were visible in the Lu³⁺ spectrum.