The Effect of Oxygen Adsorption on Photo- and Semiconduction of β-Carotene
- 1 March 1961
- journal article
- Published by AIP Publishing in The Journal of Chemical Physics
- Vol. 34 (3), 812-819
- https://doi.org/10.1063/1.1731680
Abstract
The presence of adsorbed oxygen gas increases the magnitude of the surface semiconduction currents in crystalline powder β-carotene by a factor of about 103. The activation energy for the surface semiconduction process is 1.52 ev in argon gas and is decreased to 1.29 ev in oxygen. The room temperature photo-current is increased by a factor of about 25 in oxygen over the value in argon. The activation energy of the photoconduction process is not affected by oxygen. The increase in dark current in an oxygen ambient requires a time of about 2 hr to come to the equilibrium value at room temperature. Radiation is not required to cause the increase. The effect of the oxygen can be reversed completely by heating the β-carotene to 120°C in an inert atmosphere (dry nitrogen or argon). The increase in dark current is linearly proportional to the partial pressure of oxygen in the chamber. The rate of desorption of the oxygen increases with the temperature. The resulting data yield an activation energy of desorption of 0.17 ev. It is suggested that this is the binding energy for the formation of an oxygen-carotene complex, and that the decrease in semiconduction activation energy is correlated to this binding energy. An analysis is given which leads to the conclusion that the mechanism of the current increase with formation of the oxygen complex is twofold; a decrease in the activation energy for semiconduction, and an increase in the mobility of the charge carriers. There is no evidence for a change in the charge creation process. The experimental results are considered to be a partial verification of Platt's theory on the donor-carotene-acceptor complex in photosynthesis since the triplet level of chlorophyll b has a value of 1.43 ev, midway between the value of 1.52 ev for the free carotene semiconduction activation energy and 1.29 ev for the corresponding value of the oxygen-carotene complex. It is also suggested that a possible mechanism for the carotene protection of cells from destructive photo-oxidation may be the formation of the oxygen-carotene complex.Keywords
This publication has 12 references indexed in Scilit:
- Photoconduction Activation Energies in cis-trans Isomers of β-CaroteneThe Journal of Chemical Physics, 1961
- Photoconduction and Cis-Trans Isomerism in β-CaroteneThe Journal of Chemical Physics, 1959
- Evidence for the Triplet State in Photoconductivity in AnthraceneThe Journal of Chemical Physics, 1958
- The triplet state in fluid mediaProceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, 1958
- Inhibition of Carotenoid Synthesis in Photosynthetic Bacteria: Specific Inhibition of Carotenoid Synthesis in a Photosynthetic Bacterium and its Physiological ConsequencesNature, 1958
- Photoconduction of Phthalocyanines in Presence of OxygenThe Journal of Chemical Physics, 1957
- Effect of the Gaseous Atmosphere on the Photoconduction and Semiconduction of Aromatic Hydrocarbon CrystalsThe Journal of Chemical Physics, 1956
- Effect of Gases on the Photoconductivity of AnthraceneThe Journal of Chemical Physics, 1956
- The Effect of Oxygen on the Photoconductivity of Anthracene. IIThe Journal of Chemical Physics, 1954
- The Cytological Effects of PodophyllinScience, 1947