Impulsive control of ground surface dynamics of I-3(-) in solution

Coherent control of I-3(-) ground state dynamics in ethanol and acetonitril e solutions is demonstrated. The method is based on impulsive excitation cr eating a dynamic hole employing sub 30 fsec tunable UV laser pulses. The ta rget of control was to increase the ratio of second to first harmonic spect ral 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, doub le 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 I-3(-) Chirping the probing pulses furthe r allows full mapping of the ground state coherence in phase space, pinpoin ting the position of the dynamic holes not only in coordinate space but als o in momentum. A theoretical model reconstructs the results nearly quantita tively and provides insight into the mechanisms active in achieving the con trol aims. It further demonstrates how the fundamental suppression serves t o 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 (similar to2.3) deviates considerably from the ratio of 4 predicted by Kubo line shape theory. Possible sources of this discrepanc y based upon alternative dephasing models are discussed.