Femtosecond time scale structural determinations

Both linear and nonlinear Raman spectroscopy can be combined with time-resolved detection techniques when pumping with short laser pulses [8.781. Since Raman spectroscopy allows the determination of molecular parameters from measurements of frequencies and populations of vibrational and rotational energy levels, time-resolved techniques give information on energy transfer between vibrational levels or on structural changes of short-lived intermediate species in chemical reactions. One example is the vibrational excitation of molecules in liquids and the collisional energy transfer from the excited vibrational modes into other levels or into translational energy of the collision partners. These processes proceed on picosecond to femtosecond time scales [8.77,8.79]. 

By the end of the twentieth century, the ability of research chemists to determine detailed structures of proteins and DNA systems in which electron transfer reactions can be monitored on time scales ranging from seconds down to nano-, pico-, and femtoseconds has brought Wolynes dream of a movie of an electron transfer process to the realm of possibility in biological oxidation-reduction systems. In protein chemistry several metalloen-zymes containing buried metal ions such as Fe in Fig. 2 have been modified by attaching other metal ions such as Ru(bipy)2" at various sites on the surface of the proteins... 

Zaric and HalF predicted a weakly bound structure and a strongly bound intermediate in the reaction path of the activation of methane with the fragment [Tp Rh(CO)] [Tp = HB(3,5-dimethylpyraz()lyl)5 before oxidative addition. Subsequent studies using (microsecond- to femtosecond-scale) time-resolved IR spectroscopy proved that the second intermediate has a strongly bound r -C,H moiety. Similar structures were determined for the transition states in the C-H activation of methane by the [CpM(PH3)CH3)] (M = Rh, Ir) fragment by ab initio orbital theory methods. ... 

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