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

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7.2 Applications of transition state theory 155<br />

I Separation of degrees of freedom: For separable degrees of freedom, we can write<br />

the molecular partition function as<br />

= × × × (7.41)<br />

Nuclear spin ( ) may have to be taken into account in some cases as well.<br />

I<br />

Table 7.1: Molecular partition functions.<br />

type of motion energy partition function magnitude<br />

µ <br />

translation (1-D) 2 2<br />

12 2 <br />

10 8 × <br />

8 2<br />

<br />

µ µ 2 <br />

translation (3-D) 2 <br />

2 32<br />

<br />

+ 2 <br />

+ 2 2 <br />

10 24 × <br />

8 2 2 2 <br />

µ 2 <br />

rotation (1-D) a ~ 2<br />

12<br />

2 2<br />

2 <br />

10<br />

µ ~ 2 <br />

rotation (2-D) b ~ 2<br />

2 <br />

( +1)<br />

10 2<br />

2 ~ 2 <br />

µ <br />

rotation (3-D) c 12<br />

32 2 <br />

or <br />

(<br />

~ 2 ) 12 10 3 10 4<br />

vibration d [1 − exp (− )] −1 1 10<br />

electronic <br />

P exp (− ) 1<br />

a Free internal rotor. For a hindered rotor (torsional vibrational mode), the partition function has to<br />

be determined by an explicit calculation over the hindered rotor quantum states.<br />

b Linear molecule.<br />

c Nonlinear molecule.<br />

d For each harmonic oscillator degree of freedom measured from zero-point level.

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