Improved sliced velocity map imaging apparatus optimized for H photofragments

Area of Science:

• Chemical Physics
• Atomic and Molecular Physics
• Spectroscopy

Background:

• Time-sliced velocity map imaging (SVMI) is a high-resolution technique for analyzing product kinetic energies.
• Implementing SVMI for atomic hydrogen (H) fragments presents significant challenges due to their low mass and high velocities.

Purpose of the Study:

• To develop and validate an improved ion optics design for achieving SVMI of H fragments across a wide kinetic energy range.
• To enable precise measurement of kinetic energy distributions for H atoms in chemical reactions.

Main Methods:

• Introduction of an additional electrostatic lens in the drift region for radial magnification control.
• Utilizing an accelerator region with variable dimensions for optimized spatial and temporal focusing.
• Numerical simulations of electric fields and ion trajectories for design optimization.

Main Results:

• Successful SVMI of H fragments from HBr, H2S, and CH2OH photodissociation with kinetic energies from <0.4 eV to >3 eV.
• Achieved kinetic energy resolution of ≲1%-2%, comparable to traditional velocity map imaging and SVMI of heavier products.
• Demonstrated reliable performance up to at least 6 eV kinetic energy.

Conclusions:

• The novel ion optics design effectively enables high-resolution SVMI for atomic hydrogen fragments.
• Numerical simulations accurately predict system performance, reducing the need for extensive calibration.
• This advancement expands the applicability of SVMI to a broader range of chemical dynamics studies involving hydrogen atoms.