Experiments employing pulsed high-pressure (90 bar) supersonic jet expansions into a laser REMPI time-of-flight mass spectrometer are presented. Due to the very short opening time of the high-pressure valve, a compact arrangement with moderate pumping speed requirements is sufficient, which can be used up to 50 Hz repetition frequency, still maintaining an operating pressure in the expansion chamber of ca. 10~4 mbar. p-Fluorotoluene was used as a rotational and vibrational molecular thermometerto characterize the cooling capabilities of high-pressure pulsed argon and CO_2 expansions into vacuum, spanning a wide range of stagnation pressures into the supercritical regime. Rotational and torsional temperatures were deduced from the contour of the S_0 → S_1(0-0) transition by an asymmetric-top/free-internal-rotor simulation and compared with the results of a simpler rigid-rotor asymmetric-top fit. The experiments show that average rotational temperatures of ca. 1-2 K in argon and 13-15 K in CO_2 can be reached at the highest pressures studied. The population of higher |m| torsional levels of p-fluorotoluene is clearly demonstrated by the appearance of characteristic features on the blue edge of the contours, which are more pronounced in the warmer CO_2 expansions. While the rotational temperatures in argon expansions compare well with estimated gas dynamical terminal translational temperatures, there are considerable differences in the case of CO_2. Still, the degree of internal cooling reached with CO_2 is sufficiently low, so that a setup of this kind might provide good opportunities for future studies of thermally labile low-volatile molecules to cool them to cryogenic temperatures low enough to achieve a sufficient simplification of their spectra.
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机译：提出了使用脉冲高压（90 bar）超声速射流扩展仪进入激光REMPI飞行时间质谱仪的实验。由于高压阀的打开时间非常短，因此具有适中的抽速要求的紧凑装置就足够了，可以在高达50 Hz的重复频率下使用，同时仍可保持约10 MPa的膨胀室工作压力。 10〜4毫巴。对氟甲苯被用作旋转和振动分子温度计，以表征高压脉冲氩气的冷却能力以及CO_2膨胀为真空的能力，跨越了范围广泛的停滞压力进入超临界状态。通过不对称顶部/自由内部转子仿真从S_0→S_1（0-0）过渡的轮廓推导出旋转和扭转温度，并将其与简单的刚性转子不对称顶部拟合的结果进行比较。实验表明，平均旋转温度约为。在研究的最高压力下，氩气可以达到1-2 K，CO_2可以达到13-15K。 | m |较高的人口轮廓的蓝色边缘上出现了特征性特征，清楚地证明了对氟甲苯的扭转水平，这在温暖的CO_2膨胀中更为明显。尽管氩气膨胀中的旋转温度与估计的气体动力学末端平移温度比较好，但在CO_2的情况下存在相当大的差异。尽管如此，CO_2所达到的内部冷却程度仍然很低，因此这种设置可能为将来对热不稳定的低挥发性分子进行研究提供了很好的机会，以将其冷却至足够低的低温以充分简化其低温。光谱。
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