Dissociative adsorption of hydrogen fluoride onto amorphous solid water

Area of Science:

• Physical Chemistry
• Surface Science
• Spectroscopy

Background:

• Hydrogen fluoride (HF) adsorption on ice surfaces is crucial for understanding atmospheric chemistry.
• Amorphous solid water (ASW) is a relevant model system for astrophysical ices.

Purpose of the Study:

• To investigate the adsorption of HF onto ASW films at cryogenic temperatures.
• To characterize the spectral features and intermixing of HF within ASW using RAIRS.

Main Methods:

• Reflection-absorption infrared spectroscopy (RAIRS) was used to study HF:H(2)O films on Pt(111) at 50 K.
• A classical optics model was employed for quantitative spectral interpretation.
• Isotope scrambling experiments (HF/DF with H(2)O) were conducted.

Main Results:

• A strong absorbance continuum was observed in RAIRS spectra upon HF adsorption onto ASW.
• The continuum is attributed to absorption within the film, not optical artifacts.
• Intermixing and uptake were limited to the initial molecular layers.
• Extensive isotope scrambling confirmed ionic dissociation of HF.

Conclusions:

• HF undergoes significant ionic dissociation upon adsorption and dissolution in ASW at 50 K.
• The observed spectral features are consistent with the formation of Zundel-type ions.
• The study provides quantitative insights into HF-water interactions at the molecular level.