Jahn-Teller effect in the methane cation: Rovibronic structure and the geometric phase

Area of Science:

• Quantum Chemistry
• Molecular Spectroscopy
• Chemical Physics

Background:

• Understanding the electronic and nuclear dynamics of small molecules is crucial in chemistry.
• Methane (CH4) is a fundamental molecule with a complex cation (CH4+) structure.
• Previous studies have hinted at complex dynamics within CH4+.

Purpose of the Study:

• To assign the rovibronic structure in the photoelectron spectrum of CH4.
• To analyze the effects of geometric phase and tunneling motion in CH4+.
• To determine the adiabatic ionization energy of CH4.

Main Methods:

• Infrared-vacuum ultraviolet (IR-VUV) double-resonance experiments were employed.
• An effective tunneling-rotation Hamiltonian was used for analysis.
• Theoretical and experimental level structures of CH4+ were compared.

Main Results:

• The rovibronic structure of CH4 was successfully assigned.
• The study revealed the significant effect of geometric phase in CH4+.
• Low-energy dynamics are dominated by large-amplitude tunneling between C(2v) minima.
• The rotationless ground state of CH4+ was identified as a tunneling doublet with F2 symmetry.
• The adiabatic ionization energy of CH4 was determined to be 101753.0(15) cm(-1).

Conclusions:

• The structure and dynamics of CH4+ at low energies are governed by tunneling motion.
• The geometric phase plays a crucial role in the observed spectral features.
• The findings provide a detailed understanding of methane cation spectroscopy and dynamics.