Comparative spectroelectrochemical, stopped-flow kinetic, and polarographic study of the titanium(III)-hydroxylamine reaction

Abstract

recommended to switch back and forth between intermittent and dc operation.In the intermittent mode, the lamp is operated for only a short time, nt, typically 20 X 0.01 sec = 0.2 second for the results in Table II. We found that the light output is the same and so is the stability if n and t are changed within limits to maintain the product constant. For example, if instead of twenty 15-msec pulses, sixty 5-msec pulses are used, output signal is nearly the same value and stability is constant. For short ON-times of less than 2 msec, time delay problems in lamp response and power supply responses can lower reproducibility. In our case, a 4-15 msec ON-time per period proved to be the most appropriate.Measurement Conditions. It is important when making measurements with the hollow cathode lamps to operate under experimental conditions so that sufficient photons are incident on the photomultiplier cathode during the measurement period (12). For example, if a relative standard deviation of 0.1 % is desired for each integration of n pulses, then 10s photon counts must be obtained for the selected hollow cathode time. Thus, the optical throughput and the product nt must be sufficient to provide the required number of photons for the desired precision.

Electrochemical and spectroscopic studies of cation radicals. 4. Stopped-flow determination of triarylaminium radical coupling rate constants

“…Introduction Efficient conversion of light quanta into chemical free energy requires that energy losses of the absorbing system due to luminescence and nonradiative heat production be minimized. In homogeneous solutions, intermolecular 4 Solar Energy Research Institute, Golden, Colo. 80401. electron transfer usually proceeds from the excited triplet state rather than the excited singlet state of a molecule because the lifetime of the latter is short compared with encounter times.…”

“…In fact, this has been done for a limited number of systems, specifically the spectroelectrochemical studies by Kuwana and co-workers1 and the electrochemical/ spectrophotometric rate determinations for the benzidine rearrangement carried out by Reilley2 and Nicholson,3 as well as the comparison of stopped-flow and electrochemical methods for studying the Ti(III)-hydroxylamine reaction by Murray and coworkers. 4 In an effort to better characterize the properties and reactions of triarylaminium cation radicals and to correlate homogeneous rate constants previously determined electrochemically with a totally nonelectrochemical spectroscopic method we have carried out extensive studies using both conventional visible spectrophotometric and stopped-flow techniques. The ions were generated in acetonitrile using Cu(II) as the oxidant.…”

Amperometric titrations

“…Electrogenerated titanium(III) has been used as titrant for copper(II), vanadium(V) (132), and low concentrations of molybdenum!VI) (85). One of the techniques used to study the titanium(III)-NH20H reaction was amperometric titration (201).…”

Simultaneous electrochemical-electron spin resonance measurements. II. Kinetic measurments using constant current pulse

“…A plot of S(tm)/S(ip) vs. &iip(ím/£p ~1), as shown in Figure 2, can be used to determine rate constants. Simulations for a first-order reaction are not necessary, and this curve can easily be calculated from S(iJ S(tp) exp -kjtp dt - (12) where tm > tp. As a test for convergence and accuracy of the digital simulation, calculations were made using different numbers of time increments, Mt, to simulate the current pulse.…”

“…Similar calculations could also be used for spectroelectrochemical measurements. 12 The following mechanisms are considered. The initial step in each case is the electrochemical generation of a paramagnetic intermediate R + e =$=* R"…”