Enhancement of N 2 O 4 on Porous Glass at Room Temperature: A Key Intermediate in the Heterogeneous Hydrolysis of NO 2 ? -The heterogeneous hydrolysis of NO 2 at surfaces in the atmosphere is believed to be a significant source of HONO, a key OH precursor in urban areas. In this work, the yet unknown mechanism of this reaction is studied. The results suggest that N 2 O 4 at the interface should be considered as a key intermediate in the above hydrolysis.

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.

Articles you may be interested inThe intermolecular potential energy surface for CO2-Ar: Fitting to highresolution spectroscopy of Van der Waals complexes and second virial coefficients High resolution infrared spectra of H2-Ar, HD-Ar, and D2-Ar van der Waals complexes between 160 and 8620 cm−1The structure, dissociation dynamics, and intermolecular potential energy surfaces of the He 79 Br 2 van der Waals molecule have been studied using high resolution, two color, pump-probe laser induced fluorescence spectroscopy and three dimensional quantum mechanical calculations. A conical nozzle produces higher centerline cluster densities than a standard nozzle, and allows data collection further downstream from the nozzle. This yields improved signal to noise ratios and lower Doppler widths. He 79 Br 2 is found to have a T-shaped average geometry with He to Br 2 center-of-mass distances of 3.98 Å and 4.11 Å for the X and B states, respectively, somewhat longer than previously reported. Spectra were also obtained for excitation to excited bending levels of the van der Waals coordinate. However, these spectra have yet to be rotationally assigned. Vibrational predissociation line widths for the B state of He 79 Br 2 have been measured for three new vibrational levels and range from 0.036 cm Ϫ1 for B, vЈϭ8 to 0.062 cm Ϫ1 for B, vЈϭ12. These values are somewhat larger than was expected based on previous HeBr 2 linewidth measurements for higher vibrational levels. Forms for the potential energy surface that have previously been used to simulate the spectra of HeCl 2 have been applied to the HeBr 2 data. For the HeBr 2 X state, two potentials are tested. First, a slightly anisotropic, one center Morse-Spline-van der Waals potential with angle dependent parameters is used. Second a much more anisotropic potential obtained from ab initio calculations is tested. The more anisotropic potential produces a significantly better fit to the data. The B state potential is constructed using Morse atom-atom potentials for the short range part of the He-Br interaction. This simple potential is sufficient to fit the main excitation band, but does not yield a fit to spectra involving vibrationally excited van der Waals modes.

Although the formation and reactions of gaseous nitrous acid (HONO) in the atmosphere are of great interest, it is difficult to accurately measure HONO both in the atmosphere and in laboratory systems. We report a new technique for quantifying gaseous HONO in laboratory systems. The method utilizes the reaction of gas phase HONO with an excess of HCl gas to produce nitrosyl chloride (ClNO), which is readily quantified using FTIR. HONO was formed by flowing N2 over the surface of an aqueous HCl solution and through a bed of NaNO2, then directly into a 561 L chamber. An excess of gaseous HCl was added to the chamber to initiate the reaction in N2 at room temperature and 1 atm total pressure. The loss of HONO was followed by DOAS and FTIR and the formation of ClNO was measured by FTIR. While direct measurement of HONO by FTIR is limited by uncertainties in the available infrared absorption cross sections, calibration for ClNO is readily carried out since ClNO can be synthesized with high purity. The stoichiometry for ClNO formed to HONO reacted was determined to be 0.9 ± 0.2 (1σ). The concentration−time profiles for both HONO and ClNO were fitted with a kinetics model which gave a rate constant for the reaction HONO + HCl ClNO + H2O of k 1 ≤ (1.9 ± 1.3) × 10-19 cm3 molecule-1 s-1 (2σ) at 297 K. This should be taken as the upper limit for the gas phase reaction since some contribution from heterogeneous reaction at the chamber walls cannot be conclusively ruled out.