An in situ monitoring system for plasma-induced reactions in ethanol was developed by infrared absorption spectroscopy in multiple internal reflection geometry. We monitored in situ the preferential decrease in the IR peak intensity of CH3 and OH groups in liquid ethanol. In addition, we monitored in situ the preferential inclusion of OCH3 and free OH groups deposited on a multiple internal reflection prism. Unlike optical emission spectroscopy, the IR-based technique detects non-light-emitting compounds. It presents as a powerful alternative tool for monitoring liquid-phase plasma reactions.

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Reactions involving hydrogen plasma and oxygen plasma with a self-assembled monolayer (SAM) of octadecyltrichlorosilane were investigated by infrared absorption spectroscopy in multiple internal reflection geometry. The rate of decrease of the CH 3 peak intensity is smaller than that of the CH 2 peak intensity when the SAM is exposed to hydrogen plasma. This is attributed to the formation of CH 3 components as intermediate states of the hydrogenation of the SAM during hydrogen plasma exposure. Peak intensities due to CH 2 and CH 3 components in the SAM decreased at the same rate during oxygen plasma exposure. C=O components, detected during plasma exposure, are indicated as the intermediate states of film oxidation.

Plasma is becoming increasingly adopted in bioapplications such as plasma medicine and agriculture. This study investigates the interaction between plasma and molecules in living tissues, focusing on plasma-protein interactions. To this end, the reaction of air-pressure air plasma with NH2-terminated self-assembled monolayer is investigated by infrared spectroscopy in multiple internal reflection geometry. The atmospheric-pressure plasma decomposed the NH2components, the characteristic units of proteins. The decomposition is attributed to water clusters generated in the plasma, indicating that protein decomposition by plasma requires humid air.