HIGH-RESOLUTION FTIR SPECTRUM OF THE NU(5) AND 2-NU(9) BANDS OF HNO3

The Fourier transform infrared (FTIR) spectrum of the nu-5 and 2-nu-9 bands of nitric acid (HNO3) has been measured with a resolution of 0.004 cm-1 in the frequency range of 856-910 cm-1. By fitting a total of 744 unperturbed transitions of nu-5 with a standard deviation (SD) of 0.00051 cm-1, using a Watson Hamiltonian, a set of nine improved rovibrational constants for the upper state was obtained, Some transitions of 2-nu-9 were perturbed by a Femi resonance with the nearby nu-5 state. A total of 280 unperturbed transitions of 2-nu-9 have been analyzed to provide nine rovibrational constants for the nu-9=2 state with a SD of 0.00058 cm-1. The nu-5 and 2-nu-9 bands are mainly A-type with band centres at 879.108200 +/- 0.000045 and 896.44881 +/- 0.00011 cm-1, respectively. A comparison of calculated line intensities of nu-5 with measured values gives the transition moment as 155 +/- 0.031 D and the integrated band intensity as 282 +/- 56 cm-2 atm-1 (or 68 +/- 14 km mol-1). The transition moment of the 2-nu-9 band is therefore estimated to be 0.17 +/- 0.03 D which gives an integrated band intensity of 356 +/- 71 cm-2 atm-1 (or 86 +/- 17 km mol-1).