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Physical Chemistry 3: — Chemical Kinetics — - Christian-Albrechts ...

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5.4 Advanced collision theory 118<br />

I<br />

Figure 5.14: Measurement of differential cross sections in crossed molecular beam<br />

experiments.<br />

I<br />

Differential and integral cross sections from crossed molecular beam experiments:<br />

• We define the differential cross section ( ) for scattering<br />

of products C into the solid angle element Ω at such that<br />

( ) Ω<br />

= ( )<br />

<br />

× × × ( ) × × ( ) × Ω (5.145)<br />

• Corresponding integral cross sections are obtain by integration over and .<br />

• Depending on the scattering process of interest, we distinguish between<br />

<strong>—</strong> elastic cross sections ( ): measure of the size of the molecules,<br />

<strong>—</strong> inelastic cross sections ( ):measureoftheefficiency of energy transfer<br />

processes,<br />

<strong>—</strong> reactive cross sections ( ): measure of reactivity.

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