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

5.4 Advanced collision theory 133
I
Table 5.3: Types of long-range intermolecular interactions.
system
()
charge-charge (Coulomb) () = 1 2 2
4 0
charge-dipole
( ) = −→ · −→ = − cos
4 0 2
dipole-dipole ( 1 2 )=
charge-quadrupole Θ ∝ −3
dipole-quadrupole
Θ ∝ −4
charge-induced dipole ∝ −4
quadrupole-quadrupole ΘΘ ∝ −5
induced dipole-induced dipole
∝ −6
μ 1 · μ 2 − 3(μ 1 · r)(μ 2 · r)
2
4 0 3
I Table 5.4: Long-range intermolecular interactions ( =15 D, =3Å 3 , =1,
=0;energies in kJ mol; forcomparison: =25kJ mol @ =298K).
³ ´ ³ ´
system =5Å =10Å
ion-ion 278 139
ion-dipole 17.4 4.35
ion-induced dipole 3.34 0.21
dipole-dipole 2.17 0.27
b) Lennard-Jones (6-12) potential for nonpolar molecules
A realistic intermolecular potential for non-polar molecules is the Lennard-Jones (6-12)
potential
∙ ³LJ ´12 ³ LJ
´6¸
LJ () =4 LJ − (5.198)
LJ is usually given in reduced form in units of K as
∗ LJ = LJ
(5.199)