Impulsive Control of Ground Surface Dynamics of I3-in Solution

Abstract

Coherent control of I3- ground state dynamics in ethanol and acetonitrile solutions is demonstrated. The method is based on impulsive excitation creating a dynamic hole employing sub 30 fsec tunable UV laser pulses. The target of control was to increase the ratio of second to first harmonic spectral modulations of the symmetric stretching vibrational coherences. Methods demonstrated to achieve this target include altering pulse intensity when the excitation pulses are tuned to the maximum of the absorption peak, double excitation pulses separated by half a vibrational cycle, and tuning the pumping or probing pulses to a wavelength simultaneously resonant with both absorption bands of ground state I3-. Chirping the probing pulses further allows full mapping of the ground state coherence in phase space, pinpointing the position of the dynamic holes not only in coordinate space but also in momentum. A theoretical model reconstructs the results nearly quantitatively and provides insight into the mechanisms active in achieving the control aims. It further demonstrates how the fundamental suppression serves to precisely characterize the relaxation dynamics of weak spectral features such as higher harmonics of the symmetric stretching and the antisymmetric stretching fundamental. In particular, the ratio of dephasing rates of the first two harmonics (∼2.3) deviates considerably from the ratio of 4 predicted by Kubo line shape theory. Possible sources of this discrepancy based upon alternative dephasing models are discussed.