Sensitive Low-Recoil VUV 1 + 1' REMPI Detection of ND₃

Area of Science:

• Chemical Physics
• Molecular Dynamics
• Spectroscopy

Background:

• Velocity map imaging is crucial for measuring product distributions in molecular scattering.
• High-resolution studies with cold molecular beams are limited by cation recoil during photoionization detection.
• Minimal cation recoil detection has been achieved for NO but not for other molecules like ND3.

Purpose of the Study:

• To develop a minimal-recoil detection scheme for deuterated ammonia (ND3) for cold molecule scattering experiments.
• To enable high-resolution velocity map imaging of ND3 collision products with HD.

Main Methods:

• A resonance-enhanced multi-photon ionization (REMPI) detection scheme for ND3 was developed.
• The 1 + 1' REMPI scheme utilized vacuum ultraviolet (VUV) photons (∼160 nm) generated via four-wave-mixing in Xenon.
• The ionization step wavelength was varied (434–458 nm) to probe various autoionizing neutral states of ND3.

Main Results:

• The developed REMPI scheme imparts sufficiently low recoil energy to ND3 ions for high-resolution imaging.
• Ion recoil was mapped across a range of ionization wavelengths with vibrational resolution for final ionic states.
• Rotational resolution was achieved for specific excitation energies near vibrational thresholds, with assignments to Rydberg series.

Conclusions:

• This study successfully extends minimal-recoil detection capabilities to ND3, a significant advancement for molecular scattering studies.
• The new method allows for unprecedented high-resolution imaging of ND3 collision products in cold beam experiments.
• The findings pave the way for detailed investigations of chemical dynamics involving ND3 and other molecules.