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

5.2 Kinetic gas theory 101
5.2 Kinetic gas theory
5.2.1 The Maxwell-Boltzmann speed distributions of gas molecules in 1D and 3D
I
Figure 5.2: Experimental measurement of molecular speed distribution using a rotating
disk velocity selector and an effusive molecular beam (orrifice diameter ¿ ).
I
Rotating disk velocity selector:
• Flight time of molecules with velocity between two rotating disks (distance ):
1 =
(5.55)
• Time delay of second slit with respect to first slit ( =angle, = angular velocity):
2 =
(5.56)
• Transmission only if
y
1 = 2 (5.57)
= ×
(5.58)
In practice, one uses a number of velocity selectors in series. A measurement of the 1D
speed distribution ( ) = ( )
using this method gives