Two-dimensional infrared spectra of the asymmetric stretching vibration of the sulfite ion (IMAGE)
Caption
Figure 1: Two-dimensional infrared spectra of the asymmetric stretching vibration of the SO42- ion for sodium sulfate (Na2SO4, left column) and magnesium sulfate (MgSO4, right column) in water. The strength of the vibrational excitation is plotted as a function of the excitation frequency n1 and the detection frequency n3. Yellow-red contours correspond to excitations of the fundamental vibrational transition between the v=0 and 1 states of the vibration (red arrow in the inset image at top left), while blue contours are due to overtone excitations (v=1 to 2, blue arrow). For sodium sulfate, a change in the red-yellow contour from an elliptical line shape (top left) to a more round shape (bottom left) is observed within about 300 fs. This is due to rapidly fluctuating forces exerted on the sulfate ion by the water environment. In contrast, for magnesium sulfate (right column) the elliptical line shape is preserved on this time scale. Here, fast fluctuations are largely suppressed by the presence of magnesium ions in the immediate vicinity of the sulfate ion.
Credit
MBI / Achintya Kundu
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