C4Cl: bent or linear?

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Spectroscopy

Background:

• Previous theoretical studies on the CCl3 radical's ground state structure yielded conflicting results.
• Experimental data suggested a bent ground state, but theoretical calculations were inconsistent.

Purpose of the Study:

• To accurately determine the ground state structure of the CCl3 radical.
• To resolve discrepancies between theory and experiment regarding the CCl3 radical's geometry.
• To investigate the low-lying excited states of the CCl3 radical.

Main Methods:

• Symmetry-Adapted Cluster Configuration-Interaction (SAC-CI) theory was employed for high-level electronic structure calculations.
• Density Functional Theory (DFT) was used as a complementary computational method.
• Calculations were performed to address issues of spin contamination observed in previous coupled-cluster calculations.

Main Results:

• SAC-CI calculations unequivocally support a bent ground state structure for the CCl3 radical with 2Pi symmetry.
• DFT calculations also indicate a bent ground state structure.
• The energy difference between the ground state and a nearby Sigma state was calculated to be approximately 0.2 eV.
• Calculated excitation energies align with experimental absorption peaks.

Conclusions:

• The CCl3 radical possesses a bent ground state structure, consistent with experimental findings.
• SAC-CI theory provides reliable results for the electronic structure of the CCl3 radical, overcoming limitations of other methods like CCSD.
• The study clarifies the electronic structure and spectral properties of the CCl3 radical.