作者:Birger Bohn、Cornelius Zetzsch
DOI:10.1039/a708536b
日期:——
Pulsed production of OH in a gas-phase system containing acetylene, O2 and NO resulted in biexponential OH-decay curves, indicating formation of HO2 in secondary reactions. Production and detection of OH were performed by 248 nm photolysis of H2O2 and cw-laser long-path absorption at 308 nm, respectively. Measurements were made at room temperature in O2 or N2–O2 mixtures containing 5% O2 at total pressures between 10 and 100 kPa. Analysis of the decay curves resulted in effective rate constants for the removal of OH and the formation of HO2 by acetylene in the presence of O2 in the range (1.4–3.5)×10-13 cm3 s-1, dependent on total pressure and O2 concentration. HO2 is thought to be formed from HCO and O2, with HCO originating in a reaction of an intermediate acetylene–OH adduct with O2. HO2 yields were found to vary between 1.13 and 1.01 and tending to higher values at lower total pressures. These yields are higher than the expected value of 1, which can be explained by a dissociation of a small fraction of vibrationally excited glyoxal formed, together with OH in a second channel of the acetylene–OH adduct+O2 reaction. In order to check whether the increased HO2 yields are real, CO was used instead of acetylene. In this case, an HO2 yield of 0.99 was found, in good agreement with expectations, and a rate constant of (1.66±0.25)×10-13 cm3 s-1 for the OH+CO reaction in 20 kPa O2 was determined. In addition, a rate constant for the HO2+NO reaction of (9.5±1.5)×10-12 cm3 s-1, rate constants for the OH+NO reaction in the range (1.3–7.4)×10-12 cm3 s-1, depending on total pressure, and upper limits for the rate constants of possible reactions HO2+C2H2 (k⩽5×10-15 cm3 s-1) and HO2+CO (k⩽3×10-15 cm3 s-1) were derived. Error limits include statistical (2σ) and possible systematic errors.
在含有乙炔、O2和NO的气相系统中,OH的脉冲产生导致了双指数OH衰减曲线,表明在次级反应中形成了HO2。通过248 nm光解H2O2产生OH,通过连续波激光长路径吸收在308 nm检测OH。在室温下,在总压力介于10至100 kPa之间,含有5% O2的O2或N2-O2混合物中进行测量。衰减曲线的分析得到了在O2存在下,乙炔移除OH和形成HO2的有效速率常数在(1.4-3.5)×10-13 cm3 s-1范围内,这取决于总压力和O2浓度。HO2被认为是从HCO和O2中形成的,HCO源自于乙炔-OH中间体与O2的反应。HO2的产率在1.13和1.01之间变化,并向较低的总压力下趋向更高值。这些产率高于预期的1,这可以通过一小部分振动激发态的乙二醛在乙炔-OH中间体+O2反应的第二通道中与OH一起形成后解离来解释。为了检验增加的HO2产率是否真实,使用了CO代替乙炔。在这种情况下,发现HO2产率为0.99,与预期相符,并在20 kPa O2中确定了OH+CO反应的速率常数为(1.66±0.25)×10-13 cm3 s-1。此外,得到了HO2+NO反应的速率常数为(9.5±1.5)×10-12 cm3 s-1,OH+NO反应的速率常数在(1.3-7.4)×10-12 cm3 s-1范围内,取决于总压力,以及可能反应HO2+C2H2(k⩽5×10-15 cm3 s-1)和HO2+CO(k⩽3×10-15 cm3 s-1)的速率常数的上限。误差限包括统计误差(2σ)和可能的系统误差。