Rotation/Torsion Coupling in H5(+), D5(+), H4D(+), and HD4(+) Using Diffusion Monte Carlo

Area of Science:

• Quantum Chemistry
• Molecular Spectroscopy
• Computational Physics

Background:

• Hydrogen clusters like H5(+) exhibit complex internal dynamics due to low-energy barriers to internal rotation.
• Understanding rotation-torsion coupling is essential for accurately predicting molecular properties and spectra.
• Previous studies established baseline energies for J=0, necessitating further investigation at higher rotational states.

Purpose of the Study:

• To develop and apply novel computational methods for studying rotation-torsion coupling in H5(+).
• To investigate the influence of rotational excitation and deuteration on the vibrational wave functions of H5(+).
• To extend theoretical calculations to low rotational quantum numbers (J ≤ 3).

Main Methods:

• Fixed-node approximation utilizing reduced dimensional calculations for nodal surface determination.
• State space and configuration space descriptions for wave function and internal coordinate representation.
• Diffusion Monte Carlo (DMC) method to extend calculations to low J states.

Main Results:

• Two distinct computational approaches yielded results in good agreement for J=0 energies.
• Calculations extended to J ≤ 3 revealed modest changes in vibrational wave functions across investigated rotational and vibrational excitations.
• The effects of deuteration were explored for D5(+) and its hydrogen-deuterium variants.

Conclusions:

• The developed methods accurately capture rotation-torsion coupling in H5(+).
• Internal rotation and deuteration have limited impact on vibrational wave functions at the studied excitation levels.
• The findings provide a foundation for further theoretical and experimental studies of hydrogen cluster dynamics.