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首页> 外文期刊>Plasma Sources Science & Technology >Vibrational quenching by water in a CO_2 glow discharge measured using quantum cascade laser absorption spectroscopy
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Vibrational quenching by water in a CO_2 glow discharge measured using quantum cascade laser absorption spectroscopy

机译：使用量子级联激光吸收光谱测量的CO_2辉光放电中的水通过水振动淬火

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In situ quantum cascade laser (QCL) absorption spectroscopy is used to investigate the effect of admixed water in a pulsed CO_2 glow discharge on the vibrational excitation of CO_2 and CO and the conversion of CO_2. Time-resolved transmittance spectra of the non-equilibrium CO_2 plasma are measured with a 100 μs time resolution. A custom fitting routine is used to extract the time evolution of the gas temperature, rotational temperature and vibrational temperatures of CO_2 and CO, while the CO_2 conversion is determined from measured CO_2 and CO number densities. Rotational Raman scattering is additionally performed in the centre of the reactor to verify measured rotational and vibrational temperatures from line-of-sight absorption spectroscopy. The plasma is operated at 6.7 mbar, with up to 10% water admixed, and is pulsed with a 5–10 ms on-off cycle, with a current of 50 mA supplied during the plasma on-time. Vibrational temperatures and CO_2 conversion are not significantly affected by water admixtures below 0.5%. However, the asymmetric stretch temperature of CO_2 (T_3) shows considerable quenching upon admixing 10% water vapour, with the maximum elevation above the rotational temperature (T_(rot)) decreasing from 580 ± 86 K to 230 ± 63 K. For the vibrational temperature of CO (TCO), a similar trend is measured. However, the slopes of T_3 and T_(CO) within the first few hundred μs after the start of the plasma remain unchanged, even when admixing 10% water vapour, suggesting equal excitation of the vibrational modes through e–V and V–V interactions. The conversion decreases by almost a factor of 4 when admixing 10% water. We argue that vibrational quenching of CO_2 by water can explain part of the decrease. Changes in electron density and temperature and reactions between CO and OH can also play a role.
机译：采用原位量子级联激光（QCL）吸收光谱法研究了脉冲CO_2辉光放电中混合水对CO_2和CO振动激发及CO_2转化的影响。以100μs的时间分辨率测量了非平衡态co2等离子体的时间分辨透射光谱。自定义拟合程序用于提取CO_2和CO的气体温度、旋转温度和振动温度的时间演化，而CO_2转化率由测量的CO_2和CO数密度确定。另外，在反应器中心进行旋转拉曼散射，以验证视线吸收光谱测量的旋转和振动温度。等离子体在6.7毫巴的压力下工作，混合了高达10%的水，并以5-10毫秒的通断周期进行脉冲，在等离子体通电期间提供50毫安的电流。低于0.5%的水外加剂对振动温度和CO_2转化率没有显著影响。然而，当混合10%的水蒸气时，CO_2（T_3）的不对称拉伸温度显示出相当大的淬灭，高于旋转温度（T_（rot））的最大高度从580±86 K降至230±63 K。对于CO（TCO）的振动温度，测量到了类似的趋势。然而，在等离子体开始后的最初几百μs内，T_3和T_（CO）的斜率保持不变，即使在掺入10%的水蒸气时，这表明通过e–V和V–V相互作用对振动模式的激发是相等的。当加入10%的水时，转化率几乎降低了4倍。我们认为，水对CO2的振动猝灭可以部分解释这种下降。电子密度和温度的变化以及CO和OH之间的反应也会起作用。

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