A Study of Solid CO₂/NH₃ and NH₃/H₂O by XPS

The investigation of the chemical properties of ices and ice mixtures (the term “ice” as used in this context refers to the solid phase of materials typically thought of as either gases or liquids) have become increasingly important in the areas of atmospheric science, planetary astronomy, and astrophysics. In this study, high quality CO₂/NH₃ and NH₃/H₂O films have been grown on a stainless steel cold finger using a continuous flow liquid nitrogen system. The solid (or ice) samples were formed using research grade NH₃ and isotopic ¹³CO₂ gases, and ultrapure water. The isotopic gas was used to distinguish it from any background CO₂ in the vacuum chamber. The gases were mixed in a stainless steel prechamber with the pressure monitored using an MKS capacitance manometer. The base pressure in the chamber was less than 5 × 10⁻¹⁰ T prior to deposition and upon gas introduction was increased, using a precision leak valve, to approximately 2 × 10⁻⁸ T. Films were grown at this pressure for approximately 30 min. Gas purity was monitored using a Balzers Prisma QMS 300 quadrupole mass spectrometer. The nucleated films were characterized using x-ray photoelectron spectroscopy (XPS). The reported spectra include survey and high resolution scans of the major photoelectron peaks.