Validation of the Extended Simultaneous Kinetics and Ringdown Model by Measurements of the Reaction NH₂ + NO

Abstract

The determination of rate constants for fast chemical reactions from nonexponential cavity ringdown profiles requires a consideration of the interfering laser bandwidth effect that arises if the line width of the ringdown probe laser exceeds the absorption line width of the detected species. The deconvolution of the kinetics and the bandwidth effect can be accomplished with the extended simultaneous kinetics and ringdown (eSKaR) model presented by Guo et al. (Guo, et al. Phys. Chem. Chem. Phys. 2003, 5, 4622). We present a detailed validation of this eSKaR model by a corresponding investigation of the well-known rate constant for the reaction NH2 + NO. Line profiles of the pulsed ringdown probe laser and the NH2 absorption line were determined from forward modeling of experimental ringdown profiles and verified by narrow-bandwidth laser absorption measurements. In addition, the rate constant for the title reaction was evaluated using the eSKaR model and also by means of a conventional pump-probe approach with variable time delays between the photolysis (pump) and ringdown (probe) laser pulses. The resulting room temperature rate constant for the NH2 + NO reaction, k1= (8.5 +/- 1.0) x 10(12) cm(3) mol(-1) s(-1), and the room temperature pressure broadening coefficient of NH2, = 2.27 GHz/bar, measured on the A2A1<-- X2B1 transition at wavelengths around lambda = 597 nm, were found to be in excellent agreement with the available literature data.

The story of NCN as a key species in prompt-NO formation

“…No significant pressure dependence of the absorption cross section was observed. This is consistent with PGOPHER simulations: Assuming a typical pressure-broadening coefficient of 0.6 GHz (T = 1600 K, p = 100 kPa) for a three-atomic species [81] results in a merely 6% lower peak absorption cross section compared to a Doppler-limited case when changing the pressure from 0.05 to 0.1 MPa.…”

Glyoxal Oxidation Mechanism: Implications for the Reactions HCO + O2 and OCHCHO + HO2

“…46 G is the device-specific electronic gain factor of the FM spectrometer, which has to be determined separately. Its value has been remeasured and was found to be consistent with our previous determinations.…”

Density and production of NH and NH2 in an Ar–NH3 expanding plasma jet

“…For the low working pressures in our experimental conditions, pressure broadening is negligible 59 The density of NH in the A 3 ⌸͑ Ј=0͒ ← X 3 ⌺ − ͑ Љ =0͒P 33 ͑9͒ transition can be calculated from measured integrated absorption A int ,…”