Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043, Japan.
J Phys Chem A. 2010 Mar 11;114(9):3280-6. doi: 10.1021/jp909553t.
Rotational state-selection of the asymmetric-top molecule propylene oxide was carried out using an electrostatic hexapole field of 85-cm length. Molecular beam intensities were monitored by a quadrupole mass spectrometer. It was found that beam intensities of molecular beams for pure propylene oxide and those seeded in He and in Ar increased with increasing hexapole voltages. The hexapole voltage dependence of the beam intensity, which is called the focusing curve, was interpreted by computer simulation of the trajectories of molecules in the hexapolar field due to the Stark effect, as a function of rotational temperatures of molecular beams. The calculated best fit focusing curves, when compared with the experimental results, demonstrated that the rotational temperatures, associated with the distribution of states of a given rotational angular momentum J, are similar to the translational temperatures. It was found that the M = 0 states (where M is the projection of J along the direction of the electrostatic field) and negative values of the pseudoquantum number tau of propylene oxide can be selected using our experimental setup. These results suggest that the hexapole electric field is a tool even for the selection of rotational and orientation states of asymmetric-top molecules.
采用长度为 85 厘米的静电六极场对丙烯氧化物的不对称分子进行了旋转态选择。通过四极质谱仪监测分子束强度。结果发现，纯丙烯氧化物和在 He 和 Ar 中掺杂的分子束的强度随六极电压的增加而增加。通过计算机模拟由于 Stark 效应引起的分子在六极场中的轨迹，对分子束的旋转温度作为函数解释了束强度的六极电压依赖性，即聚焦曲线。当将计算出的最佳拟合聚焦曲线与实验结果进行比较时，表明与特定旋转角动量 J 的状态分布相关的旋转温度与平移温度相似。结果发现，可以使用我们的实验装置选择 M = 0 状态（其中 M 是 J 沿静电场方向的投影）和丙烯氧化物的伪量子数 τ的负值。这些结果表明，六极电场甚至是用于选择不对称分子的旋转和取向状态的工具。
