Knowledge Bank

The band structure of the $\nu 3$ vibration of $NpF6$ between 620 and $630cm-1$ has been resolved and analyzed, using a Fourier transform spectrometer at a resolution of $0.005cm-1$ and a temperature-controlled long path length cell. The overall band contour allows estimation of the band origin and the Coriolis coupling constant. Fine structure components comprising each J manifold of the ground state are evident in many manifolds at the experimental resolution. The unique pattern of fine structure components within each rotational manifold allows assignment of the J quantum numbers and determination of fine structure scalar and tensor components. Frequencies of J manifold centers can be obtained from the spectrum for the identified rotational states between $J=12$ and $J=40$ in the P and R branches of the molecule. Regression can then be used to obtain spectroscopic constants, including the rotational constant and the exact band origin. The Q branch of $NpF6$ shows a regular progression of sub-bandheads similar to that of $UF6$. These sub-bandheads were computer simulated to extract spectroscopic constants. Empirical anharmonicity constants can also be obtained from simulation of vibrational hot band components of the Q branch. Initial data indicate that no unexpected perturbations or interactions are present in the $NpF6$ molecule.