The C ̃

Area of Science:

• Physical Chemistry
• Molecular Spectroscopy
• Quantum Chemistry

Background:

• The electronic transitions of small molecules are fundamental to understanding chemical bonding and reactivity.
• Previous studies on the C2N2 vacuum ultraviolet (VUV) transition (C̃1Bu ← X̃1Σg+) had assumed a linear excited state.

Purpose of the Study:

• To analyze the VUV C2N2 C̃1Bu ← X̃1Σg+ transition.
• To determine the geometry of the C̃1Bu excited electronic state.
• To assign vibrational bands and determine vibrational frequencies.

Main Methods:

• Analysis of vacuum ultraviolet absorption spectroscopy data.
• Spectroscopic assignment of vibrational bands.
• Determination of molecular geometry and vibrational frequencies through spectral analysis.

Main Results:

• The C2N2 C̃1Bu ← X̃1Σg+ transition is confirmed to be linear to bent.
• The C̃1Bu excited electronic state adopts a trans-bent geometry.
• The band origin is identified at 59,840 cm⁻¹.
• Vibrational frequencies for the C̃1Bu state were determined: ν1 (CN stretch) = 2055 ± 20 cm⁻¹, ν2 (CC stretch) = 979 ± 20 cm⁻¹, ν3 (trans-bend) = 542 ± 10 cm⁻¹, ν4 (torsional bend) = 131 ± 10 cm⁻¹, and ν6 (cis-bend) = 141 ± 10 cm⁻¹.

Conclusions:

• The excited C̃1Bu state of cyanogen (C2N2) is trans-bent, challenging prior assumptions.
• Detailed vibrational analysis provides key parameters for the C̃1Bu state, aiding future theoretical and experimental studies.