The Energy Levels of the v5/2v9 Dyad of HNO3 from Millimeter and Submillimeter Rotational Spectroscopy

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In this paper we show that the rotational structure of the ν5/2ν9 infrared band near 11 μm can be synthesized to high accuracy from pure rotational measurements in the millimeter- and submillimeter-wave region. The analysis uses an internal axis system Hamiltonian that accounts for the rotational dependence of the torsional splitting in 2ν9, the induced torsional splitting in ν5, and all of the infrared line positions, including those in the regions of strongest mixing and of highest excitation. This model also predicts the strength of the 2ν9 infrared band due to the strong Fermi mixing with ν5. The analysis is based on the 2317 millimeter/submillimeter lines and uses the well-documented SPFIT routines of JPL.