Infrared Studies in the 1- to 15-Micron Region to 30,000 Atmospheres

Area of Science:

• Solid-state physics
• Mineral physics
• Infrared spectroscopy

Background:

• Infrared spectroscopy is a powerful tool for analyzing molecular vibrations in solids.
• Understanding material behavior under high pressure is crucial for geology and materials science.
• Previous studies have shown pressure-induced spectral shifts in various materials.

Purpose of the Study:

• To investigate the infrared spectra of solids under high pressures up to 30,000 atmospheres.
• To analyze pressure-induced changes in vibrational modes and their implications.
• To determine the compressibility of the carbon-oxygen bond in calcite.

Main Methods:

• Construction of a specialized pressure cell utilizing type II diamonds.
• Acquisition of infrared spectra in the 1- to 15-micron region using commercial equipment.
• Analysis of spectral band shifts, intensity changes, and frequency splitting under varying pressures.

Main Results:

• Observed general trends of higher frequencies and decreased intensity for vibrational bands under pressure.
• Documented major spectral changes in calcite, including activation of the v₁ mode and splitting of v₃ and v₄ frequencies.
• Calculated the compressibility of the C-O bond length in calcite to be 2.8×10^-7/atmosphere.

Conclusions:

• The study demonstrates the capability of high-pressure infrared spectroscopy to reveal subtle and major spectral alterations in solids.
• Results for calcite suggest a pressure-induced shift of the carbonate ion from the trigonal axis.
• Comparative analysis indicated that similar spectral changes were not observed in other carbonates with calcite or aragonite structures within the studied pressure range.