Mechanisms for the far-infrared absorption in liquid methane

Area of Science:

• Computational physics
• Molecular dynamics simulations
• Spectroscopy

Background:

• Understanding the absorption spectrum of liquid methane is crucial for various chemical and physical applications.
• Previous studies have explored different contributions to the induced dipole moment, but a comprehensive model for liquid methane was lacking.

Purpose of the Study:

• To compute the time correlation function for the induced dipole moment in liquid methane.
• To identify and quantify the contributions of various induction mechanisms to the far-infrared absorption spectrum.
• To compare simulation results with experimental data for validation.

Main Methods:

• Molecular dynamics (MD) computer simulations were performed for liquid methane at 122.2 K and 25.34 mol/L.
• First-order induction mechanisms, including octupole and hexadecapole moments, field gradients, and electronic superposition, were incorporated.
• The computed absorption line shape was compared with experimental spectra.

Main Results:

• The octupole-induced dipole moment was found to be the most significant contributor to the far-infrared absorption spectrum.
• Additional induction mechanisms were identified as important for accurately modeling absorption in liquid methane.
• A satisfactory agreement between computed and experimental spectra was achieved when detailed balancing was considered.

Conclusions:

• The study successfully models the far-infrared absorption spectrum of liquid methane using molecular dynamics simulations.
• Accurate prediction requires considering multiple induction mechanisms beyond the dominant octupole contribution.
• The inclusion of detailed balancing is essential for reconciling simulation and experimental results.