Physical Chemistry Third Edition

13.6 Experimental Molecular Study of Chemical Reaction Mechanisms 611

EXAMPLE13.10

If the distance between the two disks in Figure 13.21 is 2.00 cm and if the difference in

orientation of the slots in the two disks is 15.0 degrees (0.262 radian), find the rotational

speed necessary to pass molecules with a speed of 950 m s−^1.

Solution

time of flight

0 .0200 m

950ms−^1

 2. 105 × 10 −^5 s

ω

0 .262 radian

2. 105 × 10 −^5 s

 1. 24 × 104 radians s−^1

(1. 24 × 104 radians s−^1 )

1 rev

2 πradians

 1. 98 × 103 rev s−^1

(1. 98 × 103 rev s−^1 )

(

60 s

1 min

)

 1. 19 × 105 rev min−^1

Chemical reactions can be carried out with two crossed molecular beams.

Figure 13.22 shows an apparatus for the reaction of chlorine atoms with molecules

Halogen

nozzle

Heater

Skimmer

To vacuum

To pumps

To pumps

TOF chopper

Motor

Ionizer

Quadrupole

To ion-counting

system

CI source

Figure 13.22 A Crossed-Molecular Beam Apparatus (Schematic).From R. D. Levine

and R. B. Bernstein,Molecular Reaction Dynamics and Chemical Reactivity, Oxford

University Press, New York, 1987, p. 234.