来自《耶鲁大学开放课程：新生有机化学 第5集 第5集》

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  But there's another angle
  但还有一个角度
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  at which you're sure that these two are going to be in-phase,
  可以保证两束光线是同相位的
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  and that's this angle.
  就是这个角度
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  Now how do we get to that angle?
  这角度是怎么来的?
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  So this blue line here is called the scattering vector,
  这条蓝线叫做散射矢量
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  and that's how different the arrow coming out is from the arrow going in.
  用来扫描出射光与入射光之间的变化
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  That's just a funny mathematical or geometric thing that people have defined;
  这只是个简单的几何上的概念
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  they call it the scattering vector.
  把它叫作散射矢量
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  Now this length is exactly the same as that length.
  可以看到这里的图形呈对称关系
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  This length is exactly the same as that length,
  对应角度相等 对应长度相等
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  and when you turn at a given angle,
  所以转到这个角度
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  the vector between those will be perpendicular to the direction they're going
  散射矢量与两电子的连线相垂直