Multi-photon ionisation spectroscopy for rotational state preparation of

Area of Science:

• Atomic and Molecular Physics
• Quantum Chemistry

Background:

• High-precision experiments require molecular ions in well-defined states.
• Studying the time variation of fundamental constants like the proton-to-electron mass ratio (mₚ/mₑ) necessitates precise control over molecular ion states.

Purpose of the Study:

• To investigate the 2+1' resonance enhanced multi-photon ionization (REMPI) of molecular nitrogen (N₂) via the a¹Π<0xE2><0x82><0x97>(v=6) intermediate state.
• To assess the feasibility of generating molecular nitrogen ions in a specific ro-vibrational state using this method.
• To extract molecular constants for the uncharacterized a¹Π<0xE2><0x82><0x97>(v=6) intermediate state.

Main Methods:

• Utilized 2+1' REMI spectroscopy on molecular nitrogen.
• Performed detailed spectral analysis to determine molecular constants of the intermediate state.
• Optimized laser parameters (wavelength, pulse energy) and intermediate state selection.

Main Results:

• Successfully identified and characterized the a¹Π<0xE2><0x82><0x97>(v=6) intermediate state for N₂ REMI.
• Developed a method to suppress the formation of rotationally excited molecular ions.
• Achieved high purity generation of molecular nitrogen ions in the ro-vibrational ground state.

Conclusions:

• The 2+1' REMI via the a¹Π<0xE2><0x82><0x97>(v=6) state is a viable method for producing pure molecular nitrogen ions.
• This technique offers a crucial tool for precision measurements, including the study of fundamental constant variations.
• Precise control over laser parameters and intermediate states is key to achieving high-purity ion generation.