10min:

W. F. WANG, J. MARCOS SIROTA, Joint Center for Earth Systems Technology, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250, USA; P. P. ONG AND E. C. LOOI, Department of Physics, Faculty of Science, National University of Singapore, Lower Kent Ridge Road, Singapore 119260, Singapore.

The high-resolution infrared spectrum of HNO₃ in the region of 805-853 cm^-1 has been measured and assigned for the 3₉-₉ hot band. The significant splittings in the upper state 3₉ arising from the torsional motion of H around ON were observed and identified. It was found that 3₉, which is around 1289 cm^-1, was involved in a strong Coriolis resonance with a dark state near 1301 cm^-1, apart from the slightly higher vibrational state ₄. To account for the corresponding Coriolis perturbations as well as the torsional splittings observed in the 3₉-₉ band, a comprehensive line-position fit was performed by simultaneously adjusting three sets of constants for 3_9,1, 3_9,2 and the dark state. Accurate rovibrational constants were obtained giving a fit of 947 unperturbed and 146 perturbed lines to the rms accuracy of 0.00062 cm^-1 and 0.00175 cm^-1, respectively. The interacting dark state, found at 1300.7331(19) cm^-1, can be assigned to 2₆ which proves to be responsible for the previously unjustified K_c = 6 resonance observed in the strong ₃ band.