Infrared absorptions of the H(2)O ... H(2) complex trapped in solid neon

Area of Science:

• Physical Chemistry
• Spectroscopy
• Low-Temperature Physics

Background:

• Hydrogen (H2) is typically infrared inactive due to its symmetry.
• Water (H2O) exhibits characteristic infrared absorptions.
• Previous studies suggest interactions between H2 and H2O can alter their spectral properties.

Purpose of the Study:

• To investigate the infrared spectrum of solid H2 and H2O mixtures at cryogenic temperatures.
• To identify and characterize new spectral features arising from H2-H2O interactions.
• To assign observed absorptions to specific molecular complexes.

Main Methods:

• Deposition of a neon matrix containing trace amounts of H2 and H2O at 4.3 K.
• Infrared spectroscopy to analyze the vibrational modes of the deposited sample.
• Analysis of spectral shifts and new absorption bands.

Main Results:

• An unexpected infrared absorption band for H2 was observed, indicating its vibrational fundamental became active.
• New absorptions associated with H2O vibrational fundamentals were detected.
• These new peaks were assigned to the van der Waals complex of H2O with H2.
• Complexes involving ortho-H2 (J=1) were found to be the primary contributors to the observed infrared absorptions.

Conclusions:

• The formation of a H2O-H2 van der Waals complex in a solid neon matrix is confirmed by infrared spectroscopy.
• The interaction with H2O activates the normally infrared-inactive H2 vibrational mode.
• The ortho-H2 isomer plays a significant role in the formation and spectral properties of these complexes.