The energy levels of the nu 5/2 nu(9) dyad of HNO3 from millimeter and submillimeter rotational spectroscopy

In this paper we show that the rotational structure of the nu (5)/2 nu (9) infrared band near 11 mum can be synthesized to high accuracy from pure rot ational measurements in the millimeter- and submillimeter-wave region. The analysis uses an internal axis system Hamiltonian that accounts for the rot ational dependence of the torsional splitting in 2 nu (9), the induced tors ional splitting in nu (5), and all of the infrared line positions, includin g those in the regions of strongest mixing and of highest excitation. This model also predicts the strength of the 2 nu (9) infrared band due to the s trong Fermi mixing with nu (5). The analysis is based on the 2317 millimete r/submillimeter lines and uses the well-documented SPFIT routines of JPL. ( C) 2001 Academic Press.