Showing papers by "A. R. Ravishankara published in 2006"
TL;DR: The cavity ring-down spectrometer (CaRDS) was designed and constructed for installation on the NOAA WP-3D Orion (P-3) aircraft for sensitive, rapid in situ measurement of NO3 and N2O5.
Abstract: This article describes a cavity ring-down spectrometer (CaRDS) specifically designed and constructed for installation on the NOAA WP-3D Orion (P-3) aircraft for sensitive, rapid in situ measurement of NO3 and N2O5. While similar to our previously described CaRDS instrument, this instrument has significant improvements in the signal-to-noise ratio, the time resolution, and in overall size and weight. Additionally, the instrument utilizes a custom-built, automated filter changer that was designed and constructed to meet the requirement for removal of particulate matter in the airflow while allowing fully autonomous instrument operation. The CaRDS instrument has a laboratory detection sensitivity of 4×10−11cm−1 in absorbance or 0.1pptv (pptv denotes parts per trillion volume) of NO3 in a 1s average, although the typical detection sensitivities encountered in the field were 0.5pptv for NO3 and 1pptv for N2O5. The instrument accuracy is 25% for NO3 and 20%–40% for N2O5, limited mainly by the uncertainty in the...
123 citations
TL;DR: The results are discussed in terms of a mechanism involving the formation of hydrogen-bonded complexes in which intramolecular vibrational energy redistribution can occur at rates competitive with re-dissociation to the initial collision partners in their original vibrational states.
Abstract: We report rate coefficients for the relaxation of OH(v = 1) and OD(v = 1) by H2O and D2O as a function of temperature between 251 and 390 K. All four rate coefficients exhibit a negative dependence on temperature. In Arrhenius form, the rate coefficients for relaxation (in units of 10–12 cm3 molecule–1 s–1) can be expressed as: for OH(v = 1) + H2O between 263 and 390 K: k = (2.4 ± 0.9) exp((460 ± 115)/T); for OH(v = 1) + D2O between 256 and 371 K: k = (0.49 ± 0.16) exp((610 ± 90)/T); for OD(v = 1) + H2O between 251 and 371 K: k = (0.92 ± 0.16) exp((485 ± 48)/T); for OD(v = 1) + D2O between 253 and 366 K: k = (2.57 ± 0.09) exp((342 ± 10)/T). Rate coefficients at (297 ± 1 K) are also reported for the relaxation of OH(v = 2) by D2O and the relaxation of OD(v = 2) by H2O and D2O. The results are discussed in terms of a mechanism involving the formation of hydrogen-bonded complexes in which intramolecular vibrational energy redistribution can occur at rates competitive with re-dissociation to the initial collision partners in their original vibrational states. New ab initio calculations on the H2O–HO system have been performed which, inter alia, yield vibrational frequencies for all four complexes: H2O–HO, D2O–HO, H2O–DO and D2O–DO. These data are then employed, adapting a formalism due to Troe (J. Troe, J. Chem. Phys., 1977, 66, 4758), in order to estimate the rates of intramolecular energy transfer from the OH (OD) vibration to other modes in the complexes in order to explain the measured relaxation rates—assuming that relaxation proceeds via the hydrogen-bonded complexes.
17 citations
TL;DR: In this article, the rate coefficients for the gas phase reaction of OH with OClO over the temperature range 242-392 K at 25, 50, and 100 Torr (He) were reported.
Abstract: Rate coefficients are reported for the gas phase reaction of OH with OClO over the temperature range 242–392 K at 25, 50, and 100 Torr (He). Kinetic measurements were made using pulsed laser photolysis with laser induced fluorescence detection of the OH radical. The measured rate coefficients were independent of pressure and are well represented by k1(T) = (1.43 ± 0.3) × 10−12 exp(597 ± 36/T) cm3 molecule−1 s−1 (k1(298 K) = 1.06 × 10−11 cm3 molecule−1 s−1). The quoted uncertainties are 2σ (95% confidence level) and include estimated systematic errors. Discrepancies with the previous OH + OClO rate coefficient measurement by Poulet et al. (Int J Chem Kinet 1986, 18, 847–859) are discussed. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 234–241, 2006
2 citations