Predicting OH stretching fundamental wavenumbers of alcohols for conformational assignment: different correction...

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Spectroscopy

Background:

• Predicting vibrational frequencies of alcohol conformers is crucial for understanding molecular behavior.
• Traditional methods using uniform scaling factors lack accuracy due to neglecting local chemical structure effects.
• Anharmonicity corrections are essential for precise wavenumber predictions.

Purpose of the Study:

• To develop an accurate model for predicting OH stretching fundamental wavenumbers of alcohol conformers in the gas phase.
• To improve upon existing harmonic approximation methods by including empirical anharmonicity corrections.
• To investigate the influence of local chemical structure on vibrational frequencies.

Main Methods:

• Application of empirical anharmonicity corrections to harmonic approximation calculations.
• Utilizing local chemical structure information for improved accuracy.
• Testing the model with Raman jet spectroscopy data for various alcohols.
• Comparing results from hybrid density functional and wave-function-based electronic structure methods.

Main Results:

• The model achieves high accuracy, with a mean absolute error of 1.3 cm⁻¹ and a maximum absolute error of 3 cm⁻¹ for 46 conformers across 24 alcohols.
• PBE0-D3 is identified as a well-performing and cost-effective electronic structure method for this model.
• Distinct anharmonicity correction patterns were observed between different electronic structure methods.
• Spectral splitting attributed to tunneling was resolved for propargyl alcohol.

Conclusions:

• The developed model provides a significant improvement in predicting OH stretching wavenumbers compared to uniform scaling methods.
• The local chemical structure plays a critical role in determining vibrational anharmonicity in alcohols.
• The study highlights potential deficiencies in electronic structure methods and differences in anharmonicity.
• The PBE0-D3 method offers a practical and accurate choice for implementing this predictive model.