Photoelectric method for measuring the kinetics of fast reactions
Abstract Generated abstract
This paper describes a photoelectric approach for measuring the kinetics of fast chemical reactions in continuous-flow systems. The method replaces manual movement of a monochromator and photodetector along the reaction chamber with a coordinate-sensitive photoelectric scanning device that records the distribution of monochromatic light absorption along the chamber. The authors outline an apparatus using a reagent mixer, reaction chamber, radiation source, scanning photodetector, and recording system, and discuss possible devices such as scanistors, vidicons, and optical-mechanical scanners. By enabling rapid, adjustable scanning, the method is presented as reducing measurement time and reagent consumption while improving stability and accuracy by minimizing the influence of flow-rate instability.
Full Text
PHOTOELECTRIC METHOD FOR MEASURING THE KINETICS OF FAST REACTIONS
P. I. Goskov, V. L. Ivasenko, V. K. Katanyuk, V. P. Lopatinskii, S. A. Lukovnikov, V. T. Novikov, V. A. Salikhov, Yu. K. Shelkovnikov.
(Presented by the scientific seminar of organic departments and laboratories)
Known methods for measuring the kinetics of fast reactions involve moving a monochromator and a photodetector along a reaction chamber with a continuously flowing jet and, as a result, determining the light absorption by the components of the reaction mixture along the extended reaction chamber [1].
The disadvantages of the above-known methods are that the movement of the monochromator and photodetector along the reaction chamber is carried out manually by means of a micrometric unit. As a result, the duration of the experiment increases, the consumption of reagents rises, and the accuracy of the measurements decreases because, over a long measurement time, it is difficult to ensure high stability of the velocity of the continuously flowing jet; moreover, in this case it is impossible to regulate the measurement rate over wide limits (from very short times to long ones), which greatly narrows the possibilities of this method for measuring the kinetics of fast reactions.
In order to overcome these shortcomings, the authors have developed a method based on the use, for continuous measurement of light absorption along the chamber, of a photoelectric scanning device (FSD).
Figure 1 shows a block diagram of the setup for implementing the proposed method; in Fig. 2, by way of example, the light flux that has passed through the reaction chamber and falls on the FSD is shown, and the corresponding
the output signal (video signal) from the PESC corresponding to this case.
According to Fig. 1, the block diagram of the proposed method consists of a liquid-reagent mixer 1, a reaction chamber 2, a source of monochromatic radiation 3, a photoelectric scanning device 4, and a system for recording the video signal from the PESC 5.
Fig. 1. Block diagram of an apparatus for investigating the kinetics of fast reactions by means of a PESC.
With a constant flow of reagents in mixer 1, a steady distribution of the concentrations of the components of the reaction mixture is established along the length of reaction chamber 2; this distribution is recorded from the change in the intensity of the monochromatic radiation flux by means of the photoelectric scanning device 4. Its output signal, whose envelope repeats the distribution of light absorption along the reaction chamber, is fed to the recording system 5, for example, a cathode-ray tube.
Fig. 2. Schematic representation of the intensity of the light flux incident on the PESC photodetector (a) and the video signal from the PESC corresponding to this case.
As the photoelectric scanning device one may use any coordinate-sensitive photodetector with sufficiently high speed, i.e., a photodetector with electrical or electromechanical (optical-mechanical) scanning,
for example, a vidicon, a scanistor, a Nipkow disk, etc. The basic requirement for the PhESU is the possibility of regulating the sweep time within the range from several hertz to several hundred (thousand) kilohertz. This makes it possible to study the kinetics of the most diverse types of reactions. The authors investigated and practically used only two types of PhESU: semiconductor (scanistors) and electromechanical (with scanning mirrors or disks). In the first case the sweep time was tens of microseconds, and in the second case tens of milliseconds.
The PhESUs investigated can provide the above-described measuring setup with the following technical characteristics:
- Scanning rate along chamber 2: \(10 \cdot 10^5\) Hz.
- Speed adjustment: smooth.
- Scanning duration: \((0.5 \div 0.9)(10^{-1} \div 10^{-5})\) s.
- Length of the scanning field:
a) without changing the scale optically—up to 50 mm;
b) with a change of scale—up to 500 mm. - Coordinate resolution: \(10 \div 20\ \mu\text{m}\).
- Sensitivity to luminous fluxes: from fractions of a lux to 10 lux.
- Recording of the distribution of light absorption along chamber 2:
a) on an electronic oscilloscope, or
b) on photographic film. - Spectral characteristic of the photoconverter: \(0.2\text{--}1.1\ \mu\text{m}\).
Because the measurement is carried out rapidly (the pattern of the distribution of light absorption along the reaction chamber is determined by the PhESU in fractions of a second), the influence of jet instability on the measurement results is practically completely eliminated, and as a result the accuracy and stability of the measurements are significantly increased. In addition, owing to the reduction in measurement time, reagent consumption is substantially decreased.
Thus, in the proposed method, through the use of a photodetector with electrical or electromechanical scanning, the PhESU makes it possible to eliminate the shortcomings inherent in known methods for measuring the kinetics of fast chemical reactions and caused in those methods by the use of mechanical manual scanning.
Literature
- E. Koldin. Fast Reactions in Solution. Moscow, “Mir,” 1966.