Soorkia Satchin, Liu Chen-Lin, Savee John D, Ferrell Sarah J, Leone Stephen R, Wilson Kevin R
Department of Chemistry, University of California, Berkeley, California 94720, USA.
Rev Sci Instrum. 2011 Dec;82(12):124102. doi: 10.1063/1.3669537.
A new pulsed Laval nozzle apparatus with vacuum ultraviolet (VUV) synchrotron photoionization quadrupole mass spectrometry is constructed to study low-temperature radical-neutral chemical reactions of importance for modeling the atmosphere of Titan and the outer planets. A design for the sampling geometry of a pulsed Laval nozzle expansion has been developed that operates successfully for the determination of rate coefficients by time-resolved mass spectrometry. The new concept employs airfoil sampling of the collimated expansion with excellent sampling throughput. Time-resolved profiles of the high Mach number gas flow obtained by photoionization signals show that perturbation of the collimated expansion by the airfoil is negligible. The reaction of C(2)H with C(2)H(2) is studied at 70 K as a proof-of-principle result for both low-temperature rate coefficient measurements and product identification based on the photoionization spectrum of the reaction product versus VUV photon energy. This approach can be used to provide new insights into reaction mechanisms occurring at kinetic rates close to the collision-determined limit.
构建了一种新型脉冲拉瓦尔喷嘴装置，该装置配备真空紫外（VUV）同步辐射光电离四极杆质谱仪，用于研究对泰坦和外行星大气建模具有重要意义的低温自由基-中性化学反应。已开发出一种脉冲拉瓦尔喷嘴膨胀采样几何结构的设计，该设计通过时间分辨质谱法成功用于速率系数的测定。新概念采用准直膨胀的翼型采样，具有出色的采样通量。通过光电离信号获得的高马赫数气流的时间分辨剖面表明，翼型对准直膨胀的扰动可忽略不计。在70 K下研究了C(2)H与C(2)H(2)的反应，作为低温速率系数测量和基于反应产物光电离光谱与VUV光子能量的产物鉴定的原理验证结果。这种方法可用于深入了解在接近碰撞确定极限的动力学速率下发生的反应机制。
