McCarthy Timothy J, Timko Michael T, Herschbach Dudley R
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
J Chem Phys. 2006 Oct 7;125(13):133501. doi: 10.1063/1.2202829.
Deflection by magnetic or electric field gradients has long been used to analyze or to alter the translational trajectories of neutral gas-phase atoms or molecules. Recent work has developed sources of slow, cold molecular beams that offer means to enhance markedly the attainable deflections, which are inversely proportional to the translational kinetic energy. The sensitivity and resolution can thus be much increased, typically by factors of 10(2)-10(4). We illustrate ways to exploit this enhanced deflection capability, particularly when balancing electric and magnetic deflections. Chemical scope can be greatly extended by utilizing feeble but ubiquitous interactions, especially the induced electric dipole due to the molecular polarizability and magnetic moments resulting from molecular rotation or nuclear spins. We also examine the effect of non-Maxwellian velocity distributions produced by supersonic expansions or by quantum statistics (pertinent for ultracold beams). Generic plots are provided, employing dimensionless variables, to facilitate the design and interpretation of experiments with deflections amplified by low kinetic energy.
长期以来，利用磁场或电场梯度进行偏转已被用于分析或改变中性气相原子或分子的平移轨迹。最近的研究开发出了慢速、冷分子束源，提供了显著增强可实现偏转的方法，偏转与平移动能成反比。因此，灵敏度和分辨率可以大幅提高，通常提高10² - 10⁴倍。我们阐述了利用这种增强偏转能力的方法，特别是在平衡电偏转和磁偏转时。通过利用微弱但普遍存在的相互作用，尤其是由于分子极化率产生的感应电偶极以及分子旋转或核自旋产生的磁矩，可以极大地扩展化学研究范围。我们还研究了由超声速膨胀或量子统计（适用于超冷束）产生的非麦克斯韦速度分布的影响。提供了使用无量纲变量的通用图表，以方便设计和解释通过低动能放大偏转的实验。
