HIGH RESOLUTION MEASUREMENTS AND ANALYSIS OF THE FTIR SPECTRA OF NITRIC ACID (HN03) AND ITS DEUTERA TED SPECIES (DN03)

Abstract

The infrared spectra of the ?2, ?5, and 2?9 bands of normal nitric acid (HNO3) , and the ?6, ?7, ?8, ?9, 2?9-?9, and (?6+?9)-?9 acid bands of deuterated nitric (DNO3) have been measured using the high resolution Fourier transform infrared technique. A Bomem DA3.002 interferometric spectrometer was used to record the spectra of these bands. The measured line frequencies were estimated to be accurate to within �0005 cm-1 or better. The observed infrared transitions of these asymmetric-top molecules have been assigned with quantum numbers J, Ka, and K and fitted to give upper state rovibrational constants by means of a non-linear least-squares program which uses a Watson's A-reduced rotational Hamiltonian in the Ir representation. The v2 band of HN03 has been measured with a resolution of 0.004 cm-1 in the 1657-1755 cm-1 region. A total of 4459 b-type transitions were used to obtain an improved set of 13 rovibrational constants for the upper state. The standard deviation of the fit was 0. 00035 cm-1 . The band center was found to be an order more accurate than that reported. The transition moment of the band was estimated from an integrated band intensity calculation. The spectrum of HNO3 in the 856-910 cm-1 region has been measured with 0. 004 cm-1 resolution for the study of the A-type v5 and 2v9 bands. By fitting 744 unperturbed transitions of v5 with a standard deviation of 0. 00051 cm-1, an improved set of rovibrational constants for the v5 = 1 state was obtained. For the 2v9 band, 280 unperturbed transitions have been analysed with a standard deviation of 0.00058 cm-1. The transition moment for each band has been estimated. The constants for the v8 band of DN03 have been derived for the first time from the fit of 1888 c-type transitions with a standard deviation of 0.00022 cm-1. The band centered at 762. 8738� 0001 cm-1 was measured with a resolution of 0.002 cm-1. Using a combination difference fit which includes microwave data and those from the present work, the ground state constants have been improved. Herman-Wallis factors were derived to account for an intensity anomaly observed in the spectrum. The spectrum of DNO3 has been newly measured in the v9 region (320-384 cm- 1) with a resolution of 0.0035 -1 cm. A total of 1772 c-type transitions has been fitted to give 9 constants for the upper state. An analysis was also made on the hot band 2v9 - v9 in order to obtain the constants for the v9 = 2 state. The inertial defect for the v9 = O, 1, states has been calculated. The A-type v6 and v7 bands of DN03 were recorded with 0.002 cm- 1 resolution in the 510-667 cm-1 region. A set of 10 rovibrational constants for the v7 = 1 state has been obtained from a fit of 2930 transitions, with a standard deviation of 0.00021 cm-1. For the v6 band, 1571 transitions were fitted with a standard deviation of 0.00046 cm-1. Furthermore, constants for the (v6 +v9 )-v9 band were derived. Accurate band centers were also obtained. From a combination difference fit, the ground state constants for DNO3 were further improved. Spectrum calculated from the analysis agrees well with the corresponding observed spectrum.