We report the molecular dynamics of several solvated ions present in a
queous ionic solutions (HCl, HNO3, NaCl, and NaNO3) investigated by fe
mtosecond time-resolved optical Kerr effect measurements. From the acc
urate fitting of decay curves, measured over 5-6 decades of intensity
range, it has been possible to characterize (i) an instantaneous elect
ronic response, (ii) a fast contribution of water, (iii) a rotational
relaxation of the individual ions (tau(rot) similar to 2-3 ps), and (i
v) a slow concentration-dependent decay connected to the direct ion-io
n interactions. These results will be of interest to those seeking to
measure electro-optic effects in aqueous solutions as these experiment
s give new information on the nature of the aqueous state.