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Summary form only given. Direct observation of temporally varying molecular geometries during a chemical reaction is very challenging. Ultrafast (pico- and femtosecond) laser spectroscopy allows the detection of various short living species and the determination of their lifetimes. In a recent experiment, time-dependent solvatochromic shifts and real time photography of the OH...O motions in liquid water have been observed and interpreted with statistical mechanics of nonlinear optical processes. These results mainly pointed out the vibrational solvatochromism of the (v=0->v=1) band. The purpose of this paper is to present mid-infrared laser transient spectroscopy in liquid water and to show the competition between ground state absorption and the first excited state absorption of the antisymmetric v/sub 3/ vibration.