磁场中顺磁分子的碰撞：基于物质波夫琅禾费衍射的解析模型
Collisions of paramagnetic molecules in magnetic fields: an analytic model based on Fraunhofer diffraction of matter waves
摘要：
我们研究了磁场对开壳层分子（$^2Σ$，$^3Σ$和$^2Π$）与闭壳层原子的旋转非弹性碰撞动力学的影响。我们的处理利用了物质波散射的夫琅和费模型及其最近扩展到电子碰撞[M。Lemeshko和B. Friedrich，J. Chem. Phys. \textbf{129}，024301（2008）]和辐射场[M. Lemeshko和B. Friedrich，Int. J. Mass. Spec. in press（2008）]。磁场使分子在空间固定框架中对齐，从而改变衍射目标的有效形状。这显著地影响微分和积分散射截面。我们通过评价He - CaH（$X ^2Σ^+$），He - O $_2$（$X ^3Σ^-$）和He - OH（$X ^2Π_Ω$）系统在热碰撞能量下的磁场依赖的散射特性来验证我们的治疗。由于横截面可以获得不同方向的磁场相对于相对速度矢量，该模型还提供了预测正面与侧面的空间不对称的碰撞。的空间不对称性被发现是几乎可以忽略不计的He - OH系统，弱的He - CaH碰撞，和强的He - O $_2$。在平行于相对速度矢量的磁场中，He - OH $(J=3/2,f \to J', e/f)$积分截面主要由$ΔM$的奇跃迁控制，而He - CaH（$X ^2Σ^+$）和He - O $_2$（$X ^3Σ^-$）碰撞系统则主要由$ΔM$的偶跃迁控制.对于后一种系统，磁场打开了在没有磁场的情况下关闭的非弹性通道。这些涉及$N=1, J=0 \to N', J' $与$J'=N'$的跃迁。
英文摘要：
We investigate the effects of a magnetic field on the dynamics of rotationally inelastic collisions of open-shell molecules ($^2Σ$, $^3Σ$, and $^2Π$) with closed-shell atoms. Our treatment makes use of the Fraunhofer model of matter wave scattering and its recent extension to collisions in electric [M. Lemeshko and B. Friedrich, J. Chem. Phys. \textbf{129}, 024301 (2008)] and radiative fields [M. Lemeshko and B. Friedrich, Int. J. Mass. Spec. in press (2008)]. A magnetic field aligns the molecule in the space-fixed frame and thereby alters the effective shape of the diffraction target. This significantly affects the differential and integral scattering cross sections. We exemplify our treatment by evaluating the magnetic-field-dependent scattering characteristics of the He -- CaH ($X ^2Σ^+$), He -- O$_2$ ($X ^3Σ^-$) and He -- OH ($X ^2Π_Ω$) systems at thermal collision energies. Since the cross sections can be obtained for different orientations of the magnetic field with respect to the relative velocity vector, the model also offers predictions about the frontal-versus-lateral steric asymmetry of the collisions. The steric asymmetry is found to be almost negligible for the He -- OH system, weak for the He -- CaH collisions, and strong for the He -- O$_2$. While odd $ΔM$ transitions dominate the He -- OH $(J=3/2,f \to J', e/f)$ integral cross sections in a magnetic field parallel to the relative velocity vector, even $ΔM$ transitions prevail in the case of the He -- CaH ($X ^2Σ^+$) and He -- O$_2$ ($X ^3Σ^-$) collision systems. For the latter system, the magnetic field opens inelastic channels that are closed in the absence of the field. These involve the transitions $N=1, J=0 \to N', J' $ with $J'=N'$.
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