Electric field effects on aromatic and aliphatic hydrocarbons: a density-functional study.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Spectroscopy

Background:

• External electric fields can significantly influence molecular properties.
• Understanding these effects is crucial for predicting molecular behavior in various environments.

Purpose of the Study:

• To investigate the impact of uniform static electric fields on aliphatic and aromatic molecules.
• To analyze changes in molecular geometry, dipole moments, vibrational frequencies, and electronic structure.

Main Methods:

• Density Functional Theory (DFT) with B3LYP/6-311++G(2d,2p).
• Analysis of molecular geometry, dipole moments, and infrared (IR) vibrational frequencies.
• Time-Dependent DFT (TD-DFT) for electronic transitions.

Main Results:

• Electric fields perturb molecular geometry and alter dipole moments.
• Observed molecular vibrational Stark effect, causing frequency shifts and intensity redistribution in IR spectra.
• Selective reordering of frontier orbitals (HOMO-LUMO) under moderately intense fields.
• Diminished HOMO-LUMO energy gap in molecules with pi-character LUMO beyond a threshold field.
• Increased excitation energies and decreased oscillator strengths for electronic transitions with increasing field strength.

Conclusions:

• External electric fields induce significant changes in molecular properties, including geometry, vibrational spectra, and electronic structure.
• The study provides insights into the Stark effect and field-induced orbital reordering.
• Findings are relevant for understanding molecular responses in electric fields and for designing new materials.