J. Quant. Spectrosc. R&at. TransferVol. SO, No. 3, pp. 257-266, 1993 Print4 in Great Britain. All rights resewed 0022-4073/93 $6.00 + 0.00 Copyright 0 1993 Fkrgamon Press Ltd INTEGRATED BAND INTENSITIES OF H02N02 AT 220 K RANDY D. MAY? and RANDALL R. FRIEDL Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove CA 91109, U.S.A. Drive, Pasadena, (Received 28 January 1993) Abstract-Integrated intensities of the 803, 940, 1304, 1397, 1728, and 354Ocm-’ bands of peroxynitric acid (HO,NO,) have been measured at 220 K. Simultaneously-recorded U.V. (200-350 nm) and Fourier transform i.r. (7004000 cm-‘) spectra of low-pressure gas mixtures containing HOzNOz predominantly were analyzed to determine the number densities of H02N02 in a multi-pass absorption cell within an error of approx. 10%. Absorption coefficients at 220 K in the strong 803 cm-’ band, which should be useful in the interpretation of atmospheric spectra containing spectral features of HOzN02, are also reported at high-resolution (0.003 cm-‘). INTRODUCTION Peroxynitric acid (PNA), H02N02, is postulated to be an important temporary reservoir for NOz and HO, in the stratosphere and high-latitude upper troposphere.‘” It is formed by the three-body recombination of HO* and NO, radicals HOz+NOz+M+HOzNOz+M (1) and destroyed by photolysis and reaction with OH. Fourier transform infrared (FTIR) spectra of the Earth’s atmosphere that have been recorded from balloon platforms4 and the space-shuttle5 have revealed spectral features attributed to PNA near 803 cm-‘. Analysis of the data from the initial flight of the ATMOS instrument on the Spacefub 3 shuttle mission indicated that the PNA vertical profile peaked at about 26 km near 31”N with a value of 0.35 parts-per-billion by volume (ppbv).’ This observation is consistent with model predictions within the relatively large experimen- tal uncertainties. Uncertainties in the analysis of the ATMOS data were due in large measure to the lack of spectral line parameters for the 803 cm-’ band caused by the lack of accurate laboratory measurements of the absorption coefficients in the 803 cm-’ Q-branch at the temperatures of the atmospheric observations. We have recorded U.V. (200-350 nm) and FTIR (7004000 cm-‘) spectra, simultaneously, of gas mixtures containing PNA, predominantly, at 220 K and total pressures below 0.10 torr. From the analysis of these spectra PNA number densities in a multi-pass absorption cell were determined to within an error of approx. lo%, which was limited primarily by the accuracy of the U.V. cross sections of PNA. Integrated intensities of the bands at 803, 940, 1304, 1397, 1728, and 3540 cm-’ were determined at 220 K. In addition, a high-resolution FTIR spectrum of the important band at 803 cm-’ was recorded at 220 K. This is the only band of PNA to be identified to date in atmospheric spectra. Absorption coefficients unaffected by pressure broadening are reported for the 803 cm-’ band at 0.003 cm-’ resolution (unapodized). This data should be useful for calculating PNA absorption coefficients over a range of pressures and at a temperature more relevant to the atmospheric observations. Rotational analysis of the 803 cm-’ band using the 0.003 cm-’ FTIR spectrum, together with higher-resolution diode laser spectra, is in progress. Measurements of infrared absorption coefficients of PNA at room-temperatures and at 269 K tTo whom all correspondence should be addressed. 257