Investigation of the Interaction of Water Molecules with the Surface of a Quartz Tube Using Diode Laser Spectroscopy

Abstract

The behavior of water molecules at the density of 10¹³ to 10¹⁶ cm⁻³ in a fused silica tube at room temperature has been studied. The number of molecules in the gas phase initially injected in the tube is comparable to the number of molecules adsorbed on the walls of the pre-evacuated tube. The concentrations of molecules in the gas phase were measured by diode laser spectroscopy with an external optical cavity. An off-axis alignment of the cavity with a large set number of transverse modes was used, which made it possible to measure the concentrations of molecules with narrow absorption profiles, temporal resolution of 5 s, and the accuracy better than ±5%. A strong interaction of molecules with the walls was observed. The time behavior of molecules in the gas phase both after the injection of gas into the vacuum volume and after its rapid evacuation under dynamic equilibrium between capture and desorption processes is non-exponential. The characteristic time of these processes 10⁻¹¹ to 10² s depends on the redistribution of molecules between the gas and the near-wall layers, which is governed by the physical and chemical adsorption mechanisms. The theoretical results on the kinetics of the processes are in good agreement with the experimental data.