Molecule Types Symmetric Tops Samples

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The pure rotational spectrum of the ground state of NH₃

This data file was constructed by fitting to the line positions and intensities in the HITRAN 2008 (http://www.hitran.com) database. The fit was restricted to J < 16, and is sufficient to reproduce the line positions to better than 0.001 cm^-1 and the intensities to better than 10^-20  cm² cm^-1 Molecule^-1. There are two points that are slightly non-standard:

1. The point group used is D_3h, rather than C_3v. This is necessary to account for the inversion doubling in the ground state, which appears in the data file as two vibrational states:
• s/0+ with A₁' symmetry
• a/0- with A₂" symmetry
2. To fit the K = 3n levels requires three perturbation operators:
• <0+|J+-^6|0+> = J₊⁶ + J_-⁶
• <0+|J^2J+-|0+> = J²(J₊⁶ + J_-⁶)
• <0+|J+-^12|0+> = J₊¹² + J_-¹²

1. nh3x0.pgo This has the two inversion doublets in separate manifolds (s and a), with a transition moment acting between the two manifolds. This is a good starting point for simulating electronic spectra, where the transitions will typically be from one inversion doublet or other.
2. nh3x0one.pgo This has the two inversion doublets in the same manifold. The resulting energy levels will be the same, but as the dipole moment now acts within the manifold, the Stark effect in the ground state can be simulated with this file.