Infrared measurements and calculations on H2O.HO

Area of Science:

• Spectroscopy
• Chemical Physics
• Quantum Chemistry

Background:

• The hydroxyl radical (HO) is a key reactive species in atmospheric and combustion chemistry.
• Understanding the interactions of HO with water (H2O) is crucial for modeling these environments.
• Previous spectroscopic studies have identified some vibrational modes of the H2O.HO complex, but ambiguities remained.

Purpose of the Study:

• To measure and calculate the infrared spectrum of the H2O.HO complex.
• To assign previously unobserved absorption bands.
• To elucidate the structure and vibrational properties of the H2O.HO complex in an argon matrix.

Main Methods:

• Infrared spectroscopy of H2O.HO isolated in argon matrices at cryogenic temperatures (11.5 K).
• Computational calculation of vibrational frequencies and intensities for the H2O.HO complex.
• Isotopic substitution studies (H/D) to confirm assignments.

Main Results:

• A new absorption band at 3442.1 cm⁻¹ was assigned to the OH stretch of the H2O.HO complex.
• This absorption arises from a distinct site within the argon matrix compared to previously assigned bands.
• Observed intensity changes upon isotopic substitution (D for H) align with theoretical calculations.

Conclusions:

• The study successfully assigned a new vibrational mode for the H2O.HO complex.
• The findings provide a more complete understanding of the H2O.HO interaction and its spectroscopic signature.
• This work contributes to the detailed characterization of radical-water complexes.