Infrared Absorption Cross-Section Measurements for Nitrous Acid (HONO) at Room Temperature

Abstract

Infrared absorption cross sections for nitrous acid (HONO) were measured using HONO spectra recorded simultaneously by UV/visible and FTIR spectroscopy. HONO was prepared by the reaction of HCl(g) and NaNO_2(s) and was introduced into a 561 L environmental chamber equipped with parallel sets of White optics with total path 52.5 m for UV/visible and FTIR spectroscopy. Alternatively, HONO was prepared in situ by reaction of ClNO(g) with water vapor. Absolute concentrations of HONO were determined independently using the UV spectrum and published UV absorption cross sections. All experiments were carried out at 750 Torr total pressure in N_2 at 294−297 K. We report both Q-branch intensities and integrated absorbances for the HONO modes trans-ν_3 (1263 cm^(-1)), cis-ν_4 (852 cm^(-1)), and trans-ν_4 (790 cm^(-1)). For trans-ν_3 and cis-ν_4 we also include synthetic reference spectra composed of Gaussian functions which give an accurate reproduction of our experimental references, and can easily be generated by computer for ease of use in other laboratories.

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