Conductance of a surface of chlorophyll-a in various ambient gases

For this study, we used a special electrode pattern we have described in a previous report devoted to depolarization thermocurrents flowing on a glass surface /1/. These interdigital comb-shaped electrodes were made on a pure fused silica substrate by a vacuum evaporation followed with a photochemical etching. At this step we could see the conduction current intensity of the substrate was very low, near the minimum value which could be measured on our experimental set up. Then, the chlorophyll-a was electrodeposited from the negative electrode onto the interelectrode space, according to a process stemmed from TANG and ALBRECHT'S method /2/. To prevent the specimen from being oxidized or polluted, the last processing was carried on in a vessel filled with argon at a pressure of 1.1 bar. Afterwards, all the electrical measurements were performed on the specimen stored in the vessel which could be either pumped to a secondary vacuum by means of a turbomolecular pump, or filled with a gas (carbon dioxide, argon) or a vapour (ethanol) at a monitored dynamic pressure. The I(V) characteristics were recorded using a CARY 401 electrometer and batteries as a voltage supply. Dielectric losses and capacitance were measured using a GENERAL RADIO 1621 transformer bridge. For illuminating the specimen, we used a white light from a tungsten-halogen lamp.