HTFFR kinetics studies of Sn/N2O, a highly efficient chemiluminescent reaction

Abstract

High temperature fast-flow reactors (HTFFR) were used to study the Sn/N2O reaction from 300–950 K at pressures from 4 to 110 Torr. The observed emissions are SnO[a 3Σ+(1) –X 1Σ+] and (b 3Π–X 1Σ+). The photon yield of the former system is 0.53±0.26 independent of T, that of the latter (5.9±2.9) ×10−1 exp[−(1200±200)/T]. Comparison of the photon yields of N2O- in-excess experiments, where [Sn] is measured in absorption, to experiments where Sn is in excess allows determination of oscillator strengths for the ground electronic states of Sn: f[Sn(3P0) (286.4 nm)]=0.20±0.10 and f[Sn(3P1) (300.9 nm)]=0.052±0.026, in good agreement with literature values. At T≳950 K, emission from SnO(c–X 1Σ+) and (A 1Π–X 1Σ+) is observed, apparently due to N2O decomposition followed by Sn/O2 reaction. Quenching rate coefficients at ≈900 K for SnO (a) are determined to be kQN2(a)⩽2.3×10−16; kQAr(a)⩽4.0×10−16; kQN2O(a)⩽4.0×10−14; kQSn(a)⩽4.0×10−12 ml molecule−1 s−1 based on τrad(a)⩾2.5×10−4 s. For SnO (b) the data yield τbkQN2(b) =4.8×10−20; τbkQAr(b)⩽2.0×10−20; τbkQN2O(b)⩽1.0×10−17; τbkQSn(b)⩽1.0×10−15 ml molecule−1. The overall Sn(3P0)/N2O reaction (production of all states) proceeds with a rate coefficient (8.9±4.0)×10−13 exp [−(2260±180)/T] ml molecule−1s−1. Approximate overall rate coefficients are reported for Sn(3P1)/N2O, Sn(3P0)/NO2, and Sn(3P0,1)/O2.

The N(4S) + N2O(X̃1∑) reaction

“…⌬H ϭ Ϫ367, Ϫ 78, Ϫ 72 kJ mol [4,14,15] 298 (4) is known to proceed to at least (53 Ϯ 26)% to 3 ϩ a ͚ (1) molecules in the 300 -950 K domain with a smaller percentage going to b 3 ⌸ molecules [16]. This work is supported by the U.S. Army Research Office under grants DAAD 19-99-1-0209 and DAAG55-98-1-0183.…”

Carbon, Silicon, Germanium, Tin, and Lead (Group IVA)

“…65 ' 66 These high temperature fast flow reactor systems (described in Chapter 7) allow the study of metal atom reactions in the gas phase at temperatures ranging from ~25° to 1400°C. These studies so far have been mainly concerned with metal atom abstraction-oxidation processes.…”

“…For example, the Sn + N 2 0 reac tion has been carefully studied using kinetic methods. 65 ' 66 Chemiluminescence from the SnO* formed was employed as a reaction monitor as studies were carried out in the 25°-680°C range and 4-110 torr range. At the higher temperatures, Sn + N 2 0…”

“…65,66 The importance of these studies relates to the possible generation of new chemical lasers. Kinetics and chemiluminescence are the important features rather than the production of new compounds.…”

Factors affecting the accuracy of rate coefficients of metal atom oxidation reactions in heated flow tubes

“…5,14 Here, the moderating effect of high TR and P on errors in line absorption measurements of [Me] and [Me] kv is the absorption coefficient of Me; l the optical path length; pQ the line center frequency; ArD the Doppler width = (2r0(2 R In 2)1/2/c)(TR/MMe)1/'2; C2 is a constant; a = (TL/TR)1/2; R is the universal gas constant; MMe the molecular weight of Me; c the speed of light; and TL the lamp (emitter) temperature. The absorption coefficient, k" is expressed as a Voigt profile15 to account for thermal and pressure broadening effects: a0 k,i = (M-7r £ «o2 + (wy)' dy (6) where k0 is the line center absorption coefficient /e"="0, y is a variable of integration related to the frequency,15 and a0 is the pressure broadening parameter: [OX] and [M] are calculated from the measured flow rates of the gases, flow tube pressure, and temperature:…”