A Quantum Mechanical Approach to the Computation of Rovibrational Spectra of Diatomic Molecules in Strong Magnetic Fields

Understanding how molecules behave in intense magnetic fields is essential for interpreting spectroscopic data from astrophysical objects like white dwarfs and neutron stars. While electronic structures in these fields have been studied, there has been a lack of reliable, fully quantum mechanical protocols for calculating the resulting rovibrational spectra. This paper addresses that gap by providing a framework to model these spectra across all magnetic field strengths.

The researchers extended the Wilson-Hamiltonian framework—a method originally from lattice gauge theory—to a three-dimensional grid. By using the Peierls substitution, they ensured that the nuclear Hamiltonian remains gauge-invariant, allowing for accurate calculations regardless of the choice of gauge origin. The team integrated this with electronic potential energy surfaces computed using London atomic orbitals, enabling them to capture the non-perturbative coupling between particle motion and the magnetic field. This approach allows for the explicit calculation of electric quadrupole transition moments, which are necessary to determine spectral selection rules and intensities.

The study demonstrates that strong magnetic fields induce significant changes in molecular spectra, including peak shifting, splitting, and the emergence of new transitions. By treating both electrons and nuclei quantum mechanically, the authors identified physical phenomena such as the stiffening of chemical bonds, the creation of rotational barriers, and field-induced symmetry breaking. These results provide a high-resolution computational benchmark for H2 that is suitable for interpreting experimental data in extreme magnetic environments, where classical molecular dynamics approaches often fail to capture accurate transition intensities or selection rules.

This methodology is a critical step forward for astrochemical modeling and high-field spectroscopy. By moving beyond classical trajectories and incorporating quantum nuclear effects, the framework allows researchers to predict how magnetic fields reshape the potential energy landscape of molecules. This provides a necessary tool for identifying molecular species in the intense magnetic fields found on the surfaces of magnetars and other highly magnetized astrophysical bodies.

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