Ultrasonic relaxation pulse technique

Pulse ultrasonic relaxation method, 32 18 Pump-and-probe techniques, 46 137 Purification, of actinide metals, see Actinide, metals, purification XjPj Purified protein, 36 94 Purple acid phosphatases, 40 371, 376, 43 362, 395-398, 44 243-245 biological function, 43 395 homology, 43 397... 

The spin-equilibrium dynamics of iron(III) complexes in solution have been examined with the techniques of Raman laser temperature-jump, ultrasonic relaxation, and photoperturbation. The complexes investigated, the relaxation times observed, and one of the derived rate constants are presented in Table IV. Many of the relaxation times are quite short, and some of the original temperature-jump results (45) were found to be inconsistent with more accurate ultrasonic experiments (20) and later photoperturbation experiments (102). It has not been possible to repeat some of these laser temperature-jump observations. Instead, the expected absorbance changes and isosbestic points were found to occur within the heating rise time of the laser pulse, consistent with the ultrasonic and photoperturbation experiments (20). Consequently, none of the original Raman laser temperature-jump results is included in Table IV. 

Apart from the temperature-jump technique, other relaxation methods that have been used are those of ultrasonic absorption" " and electric-field pulse. Another technique that has been used for some of the more slowly included guest molecules is that of stopped-flow. ... 

By the same technique of resonance and pulsed ultrasonic perturbation Beattie et al.176) have also studied the spin crossover dynamics in aqueous solutions of [Fe(paptH)2]Cl2- Relaxation times of ca. 40 ns were measured at 25 °C, again independent of concentration and thus presumably arising from a unimolecular spin isomerization process. Some of the thermodynamic parameters of particular interest are here AH0 = 3.91 kcal mol-1, AS° = 14.8 eu, AH = 7.63 kcal mol-1, AH = 3.72 kcal mol-1,, , = 10-2S. 

Chemical relaxation methods are widely used to study the kinetics of fast chemical reactions in solution. In particular, ultrasonic absorption techniques have been used to investigate fast exchange processes with relaxation times in the range 0.3 xs to 0.3 ns. The longer end of this time range has become accessible in recent years through the use of cylindrical resonator methods [1] which have lowered the frequency range covered by fictional pulse echo methods. 

In this work, we measured ultrasonic velocity and absorption in furan and cyclohexane mixtures over a range from 60 to 700 MHz using high-resolution Bragg reflection technique. Also used cooperatively were Brillouin scattering and pulse-echo-overlap techniques. In this binary system, small amount of cyclohexane increases substantially the relaxation frequency of furan. 

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