Far-infrared absorption by collisionally interacting nitrogen and methane molecules.

Area of Science:

• * Molecular Spectroscopy
• * Quantum Chemistry
• * Gas Phase Dynamics

Background:

• * Rototranslational enhancement spectra provide insights into intermolecular interactions.
• * Theoretical dipole functions are crucial for accurate spectral calculations.
• * Previous studies highlighted discrepancies in nitrogen-methane spectral analysis.

Purpose of the Study:

• * To perform quantum line shape calculations for nitrogen-methane gaseous mixtures.
• * To evaluate the accuracy of a recent theoretical dipole function.
• * To investigate the contribution of induction mechanisms to spectral features.

Main Methods:

• * Quantum line shape calculations were employed.
• * A theoretical dipole function incorporating multipolar induction and dispersion forces was utilized.
• * Calculated spectra were compared with experimental measurements across a temperature range (126–297 K).

Main Results:

• * Calculations based on the theoretical dipole function showed a significant intensity defect at high frequencies (>250 cm(-1)).
• * This defect persisted despite accounting for long-range induction mechanisms.
• * The findings align with previous observations for the nitrogen-methane pair.

Conclusions:

• * The current theoretical dipole function, while accounting for key induction mechanisms, is insufficient to fully reproduce experimental absorption spectra of nitrogen-methane.
• * Further refinement of theoretical models for intermolecular dipole functions is needed for accurate spectral predictions.
• * The study underscores the complexity of intermolecular interactions in gaseous mixtures.