Core excitations of biphenyl.

Area of Science:

• Physical Chemistry
• Molecular Spectroscopy
• Quantum Chemistry

Background:

• Biphenyl is a fundamental aromatic molecule with unique electronic and structural properties.
• Understanding core-level electronic excitations is crucial for characterizing molecular electronic structure.
• Previous studies on similar molecules provide context for interpreting biphenyl spectra.

Purpose of the Study:

• To present and theoretically analyze high-resolution C(1s) near-edge X-ray absorption and X-ray photoionization spectra of free biphenyl.
• To assign observed spectral features by correlating experimental data with theoretical calculations.
• To investigate the influence of chemical shifts, vibronic effects, and vibrational modes on spectral profiles.

Main Methods:

• High-resolution C(1s) near-edge X-ray absorption spectroscopy (XAS).
• High-resolution X-ray photoionization (XPI) spectroscopy.
• Theoretical analysis including finite lifetime broadening and vibronic coupling calculations.

Main Results:

• Spectral features are influenced by chemical shifts and vibronic effects, with limited resolution of vibrational fine structure due to broadening and overlapping contributions.
• Core-level spectra of biphenyl do not exhibit contributions from dihedral modes, unlike valence level photoionization.
• C-H stretching modes are significantly enhanced in core excitation spectra, while C-C stretching modes are reduced compared to naphthalene.

Conclusions:

• The study successfully assigns spectral features in biphenyl's core-level X-ray spectra.
• Vibronic effects and chemical shifts play a dominant role in shaping spectral profiles.
• The observed differences in vibrational mode contributions provide insights into the electronic structure and dynamics of biphenyl.