Rovibrational spectroscopy of the CH⁺-He and CH⁺-He₄ complexes

Area of Science:

• Physical Chemistry
• Molecular Spectroscopy
• Quantum Chemistry

Background:

• Weakly bound complexes are crucial for understanding intermolecular forces.
• Carbon hydride ions (CH+) are important in astrochemistry and fundamental chemical physics.
• Spectroscopic characterization of small molecular ions provides insights into their structure and bonding.

Purpose of the Study:

• To investigate the structure and vibrational properties of CH+-He and CH+-He4 complexes.
• To utilize infrared predissociation spectroscopy to probe these weakly bound systems.
• To determine the geometric configuration of CH+ interacting with helium atoms.

Main Methods:

• A cryogenic 22-pole ion trap apparatus was employed.
• A table-top pulsed infrared (IR) laser source was used for excitation.
• Infrared photodissociation spectroscopy was performed at 4 K.
• The C-H stretching vibrations were analyzed in the 2720-2800 cm-1 range.

Main Results:

• The infrared photodissociation spectrum of CH+-He confirmed a T-shaped structure with a band origin at 2745.9 cm-1.
• Perpendicular transitions were observed for CH+-He, consistent with a near-prolate top rotor.
• For CH+-He4, parallel transitions indicated the C-H stretch along the symmetry axis of an oblate top.

Conclusions:

• The study successfully determined the structures of CH+-He and CH+-He4 complexes.
• The results provide valuable data for theoretical calculations and understanding ion-atom interactions.
• Predissociation spectroscopy in a cryogenic ion trap is a powerful technique for studying weakly bound molecular ions.