Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published June 21, 2012 | Supplemental Material
Journal Article Open

Kinetics of n-Butoxy and 2-Pentoxy Isomerization and Detection of Primary Products by Infrared Cavity Ringdown Spectroscopy

Abstract

The primary products of n-butoxy and 2-pentoxy isomerization in the presence and absence of O_2 have been detected using pulsed laser photolysis-cavity ringdown spectroscopy (PLP-CRDS). Alkoxy radicals n-butoxy and 2-pentoxy were generated by photolysis of alkyl nitrite precursors (n-butyl nitrite or 2-pentyl nitrite, respectively), and the isomerization products with and without O_2 were detected by infrared cavity ringdown spectroscopy 20 μs after the photolysis. We report the mid-IR OH stretch (ν_1) absorption spectra for δ-HO-1-C_4H_8•, δ-HO-1-C_4H_8OO•, δ-HO-1-C_5H_(10)•, and δ-HO-1-C_5H_(10)OO•. The observed ν_1 bands are similar in position and shape to the related alcohols (n-butanol and 2-pentanol), although the HOROO• absorption is slightly stronger than the HOR• absorption. We determined the rate of isomerization relative to reaction with O_2 for the n-butoxy and 2-pentoxy radicals by measuring the relative ν_1 absorbance of HOROO• as a function of [O_2]. At 295 K and 670 Torr of N_2 or N_2/O_2, we found rate constant ratios of k_(isom)/k_(O2) = 1.7 (±0.1) × 10^(19) cm^(–3) for n-butoxy and k_(isom)/k_(O2) = 3.4(±0.4) × 10^(19) cm^(–3) for 2-pentoxy (2σ uncertainty). Using currently known rate constants k_(O2), we estimate isomerization rates of k_(isom) = 2.4 (±1.2) × 10^5 s^(–1) and k_(isom) ≈ 3 × 10^5 s^(–1) for n-butoxy and 2-pentoxy radicals, respectively, where the uncertainties are primarily due to uncertainties in k_(O2). Because isomerization is predicted to be in the high pressure limit at 670 Torr, these relative rates are expected to be the same at atmospheric pressure. Our results include corrections for prompt isomerization of hot nascent alkoxy radicals as well as reaction with background NO and unimolecular alkoxy decomposition. We estimate prompt isomerization yields under our conditions of 4 ± 2% and 5 ± 2% for n-butoxy and 2-pentoxy formed from photolysis of the alkyl nitrites at 351 nm. Our measured relative rate values are in good agreement with and more precise than previous end-product analysis studies conducted on the n-butoxy and 2-pentoxy systems. We show that reactions typically neglected in the analysis of alkoxy relative kinetics (decomposition, recombination with NO, and prompt isomerization) may need to be included to obtain accurate values of k_(isom)/k_(O2).

Additional Information

© 2012 American Chemical Society. Special Issue: A. R. Ravishankara Festschrift. Received: December 15, 2011. Revised: April 23, 2012. Publication Date (Web): April 24, 2012. Financial support was provided by the NASA Upper Atmosphere Research Program Grants NAG5-11657, NNG06GD88G, and NNX09AE21G, National Science Foundation grant CHE-0957490 and the California Air Resources Board Contracts 03-333 and 07-730. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract to the National Aeronautics and Space Administration. M.K.S. thanks the Department of Defense NDSEG Graduate Fellowship for funding. E.R.G. was supported by an EPA STAR Graduate Research Fellowship. Support from the NASA UARP and Tropospheric Chemistry Program is acknowledged. A.K.M. thanks the NASA Earth System Science and NSF Graduate Research Fellowship programs. M.L.W. thanks the Caltech Student- Faculty Programs office for funding through the Summer Undergraduate Research Fellowship program. We thank Todd Fuelberth and Dave Natzic for building the OPA crystal rotation mechanism and other technical assistance, David Robichaud for LabVIEW programming, Ralph Page for optimization of the spectrometer optics, Nathan Eddingsaas for assistance with FTIR analysis of the 2-pentyl nitrite, Michael Roy for machining of the CRDS mirror mounts, Tom Dunn for electronics assistance, and Richard Gerhart for glassware construction and repair.

Attached Files

Supplemental Material - jp212136r_si_001.pdf

Files

jp212136r_si_001.pdf
Files (461.9 kB)
Name Size Download all
md5:43c5919414a4f482468bf501a56002d6
461.9 kB Preview Download

Additional details

Created:
August 19, 2023
Modified:
October 17, 2023