r
Internuclear distance in a diatomic molecule
R
The distance between center of mass in a complex
R e
Equilibrium distances corresponding to the potential well depth of a
vdW complex
R 0
Equilibrium distances corresponding to the n = 0 vdW modes
R
Gas constant
r e
Internuclear equilibrium distance
R
nm
e
Electronic transition matrix element
R v0v00
R-centroid
Rg
Rare gas atom
s
Electron spin
s
Electron spin momentum
S
Total spin quantum number
S
Total spin angular momentum
ss
Steady-state (stationary)
T
Kinetic energy
T
Temperature
T e
Electronic term
T v
Oscillation period
b
TKinetic energy operator
V
Volume
V
Velocity of the relative motion of the species
V rel
Relative velocity vector
À
VAB
Average relative velocity of the species A and B
b
V
Potential energy operator
b
V
Perturbation operator
v
Vibrational quantum number
u
Ungerade
U
Potential energy
u
Velocity vector
U(R)
Interaction potential
U k (Q)
Energy of the k th state
U LÀJ R
ð Þ
Lennard-Jones potential
X
A
i
Distribution over quantum number of species A
z II
Number of binary collisions
z III
Number of triple collisions
Z
Number of collisions needed for the complete relaxation
Greek
a
Parameter of Morse potential
a A
Polarizability of species A
xviii
Symbols