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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Unimolecular dissociation of formyl radical, HCO -> H plus CO, studied over 1-100 bar pressure range
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Unimolecular dissociation of formyl radical, HCO -> H plus CO, studied over 1-100 bar pressure range

机译：在1-100 bar的压力范围内研究了甲酰基自由基HCO-> H加CO的单分子解离

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Unimolecular dissociation of formyl radical, HCO --> H + CO (1), was studied using pulsed laser photolysis coupled to transient UV-vis absorption spectroscopy. One-pass UV absorption, multipass UV absorption, and cavity ring down spectroscopy in the red spectral region were used to monitor temporal profiles of the HCO radical. A heatable high-pressure flow reactor of a new design was employed. Reaction I was studied over a buffer gas (He) pressure range 0.8-100 bar and a temperature range 498-769 K. Formyl radicals were prepared by pulsed photolysis of acetaldehyde and propionaldehyde (308 nm, XeCl excimer laser, 320 nm, doubled dye laser). In addition to formyl radicals monitored at 230 and 613.8 nm, methyl radicals were monitored via absorption at 216.5 nm. The initial concentrations of free radicals were varied between 7 x 10(10) and 8 x 10(13) molecules cm(-3). The obtained second-order rate constant at 1 bar is k(1)(He) = (0.8 +/- 0.4) x 10(-10) exp(-66.0 +/- 3.4 kJ mol(-1)/RT) cm(3) molecule(-1) s(-1) (498-769 K). The low-pressure data of this study were combined with those from a high-temperature shock tube study and the low-temperature data on the reverse reaction to yield k(1)(He) = (0.60 +/- 0.14) x 10(-10) exp(-64.2 +/- 1.4 kJ mol(-1)/RT) cm(3) molecule(-1) s(-1) over an extended temperature range, 298-1229 K. The dissociation rate constants measured in this work are lower than previously reported by a factor of 2.2 at the highest temperature of our measurements and a factor of 3.5 at the low end. Our experimental data indicate a pressure dependence of the second-order rate constant for the dissociation of formyl radical (1), which is attributed to pressure falloff expected from the theory of isolated resonances.
机译：使用脉冲激光光解结合瞬态UV-vis吸收光谱法研究了甲酰基自由基HCO-> H + CO（1）的单分子解离。在红色光谱区域中使用单程UV吸收，多程UV吸收和腔衰荡光谱来监测HCO自由基的时间分布。采用了一种新设计的可加热高压流动反应器。在缓冲气体（He）压力范围为0.8-100 bar和温度范围为498-769 K的条件下研究了反应I。通过脉冲光解乙醛和丙醛（308 nm，XeCl准分子激光，320 nm，双染料）制备甲酰基自由基激光）。除了在230和613.8 nm处监测到甲酰基外，还通过216.5 nm处的吸收来监测甲基。自由基的初始浓度在7 x 10（10）和8 x 10（13）分子cm（-3）之间变化。在1 bar下获得的二级速率常数为k（1）（He）=（0.8 +/- 0.4）x 10（-10）exp（-66.0 +/- 3.4 kJ mol（-1）/ RT）cm （3）分子（-1）s（-1）（498-769 K）。将这项研究的低压数据与高温冲击管研究的低压数据相结合，并将逆向反应的低温数据合并为k（1）（He）=（0.60 +/- 0.14）x 10（ -10）exp（-64.2 +/- 1.4 kJ mol（-1）/ RT）cm（3）分子（-1）s（-1）在298-1229 K的扩展温度范围内。测得的解离速率常数在我们的测量最高温度下，这项工作比以前报道的要低2.2倍，在低端则要低3.5倍。我们的实验数据表明，甲酰基自由基（1）离解的二阶速率常数与压力有关，这归因于孤立共振理论所预期的压力下降。

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