Disclaimer: This material is being kept online for historical purposes. Though accurate at the time of publication, it is no longer being updated. The page may contain broken links or outdated information, and parts may not function in current web browsers. Visit espo.nasa.gov for information about our current projects.

 

Measurements of the Rate Constant of HO2 + NO2 + N2 f HO2NO2 + N2 Using...

Christensen, L., M. Okumura, S. P. Sander, R. R. Friedl, C. E. Miller, and J. J. Sloan (2004), Measurements of the Rate Constant of HO2 + NO2 + N2 f HO2NO2 + N2 Using Near-Infrared Wavelength-Modulation Spectroscopy and UV-Visible Absorption Spectroscopy, J. Phys. Chem. A, 108, 80-91, doi:10.1021/jp035905o.
Abstract: 

Rate coefficients for the reaction HO2 + NO2 + N2 f HO2NO2 + N2 (reaction 1) were measured using simultaneous near-IR and UV spectroscopy from 220 to 298 K and from 45 to 200 Torr. Using the data acquired in the present experiment, the low-pressure and high-pressure limit rate constants for reaction 1 were determined to be ko ) (2.1 ( 0.1) × 10-31 × (T/300)-(3.1(0.3) cm6 molecule-2 s-1 and k∞ ) (2.4 ( 0.1) × 10-12 × (T/300))-(1.9(0.5) cm3 molecule-1 s-1, using the expressions for rate constants adopted by the NASA data evaluation panel (Fc ) 0.6). The reaction rate was significantly enhanced in the presence of methanol due to a chaperone effect involving an HO2‚CH3OH complex. Enhancement parameters for this process were quantified as a function of temperature. During the course of our studies, we observed an unexpected timedependent UV absorption unaccounted for in previous examinations of reaction 1 that employed UV spectroscopy to monitor HO2. We show that this absorption, which may have led to errors in those prior studies, is due to the process NO2 + NO2 a N2O4 (reaction 3). Using UV-visible spectroscopy, we determine k-3 to be (36 ( 10) s-1 at 231 K and 100 Torr using the NASA-recommended equilibrium constant for the dimerization of NO2. This represents the first measurement of k-3 at T < 250 K.

PDF of Publication: 
Download from publisher's website.
Research Program: 
Tropospheric Composition Program (TCP)
Upper Atmosphere Research Program (UARP)