It is interesting to compare the D
E;v E
0
values of the ArI 2 (E,v E ,n E ) (410–
415 cm
−1 ), KrI 2 (E,v E ,n E ) (663–683 cm
−1 ) and N 2 I 2 (E,v E ,n E ) (449– 478 cm
−1 ). The
long-range, * R
−4 , interaction between the I 2 ðE0
þ
g À D0
þ
u Þ transition electric
dipole moment and the permanent electric quadrupole moment a of N 2 (H= 1.5
10
−26
esu) can be strong in these case if the E,v E and D,v D vibronic levels are
near-resonant (R is the distance between centers of mass of the colliding partners).
The EP channel (6.3.23) has to prevail in this case (see Sect. 5.3.2.5 in [18]).
Besides, dispersion, * R
−6 , interaction has to be strong for all, M = Ar, Kr, N 2 ,
partners due to huge dipole moment of the I 2 ðE0
þ
g À D0
þ
u Þ transition, l E-D % 25
10
−18
esu and, hence, giant polarizability a I 2 E
ð Þ % 2 Á 10
5 ˚
A
3 of the I 2 (E) state.
Binding energies of the complex have to be proportional to the l EÀD
j
j
2 a M products,
a M = 1.64 (Ar), 1.77 (N 2 ), 2.48 (Kr), units, Å
3 , are polarizabilities of the partners
(see above and Fig. 6.32).
One sees, that dispersion interaction prevails in the N 2 I 2 (E,v E ,n E ) complexes
since:
the EP channel (6.3.23) has very low probability,
the N 2 I 2 (E,v E ,n E ) binding energy is larger than that of ArI 2 (E,v E ,n E ) and less than
KrI 2 (E,v E ,n E ).
To examine in what N 2 I 2 isomer transitions in the complex occur, calculation of
the N 2 I 2 (X) PES taking into account its linear, parallel, T-shaped and trapezoidal
isomers. It was shown that the parallel N 2 I 2 (E) isomer is observed in the experiments, probably. The low energy barrier between trapezoidal and parallel isomers
results in free rotor vibrational state. Both C 2v and C s symmetry are realized, so EP
channels (3.6.21, 3.6.22) are allowed.
6.4 Rare Gas-Halogen Molecule Clusters
6.4.1 Rg
1
x Rg
2
y I 2 Clusters
The first studies of the weakly-bound clusters were carried out by D.H. Levy and
coworkers [103, 125, 127, 128]. It was shown, in particular, that there are blue
shifts in excitation spectra of VP product luminescence
Ne x He y I 2 B; v B
X; 0
ð
Þ ;
ð6:4:1Þ
m – m 0 % 6.25x + 3.67y (cm
−1 ), x
4, y
4, v B = 13–26 [103]
Ar x He y I 2 B; v B
X; 0
ð
Þ ;
ð6:4:2Þ
m– m 0 % 13.5x + 3.8y (cm
−1 ), x
3, y
2, v B = 21, 22 [128] clusters. Here, m
is a wavenumber of the excitation band maximum, and m 0 is a wavenumber of the
6.3 Van der Waals Complexes
251
E;v E
0
values of the ArI 2 (E,v E ,n E ) (410–
415 cm
−1 ), KrI 2 (E,v E ,n E ) (663–683 cm
−1 ) and N 2 I 2 (E,v E ,n E ) (449– 478 cm
−1 ). The
long-range, * R
−4 , interaction between the I 2 ðE0
þ
g À D0
þ
u Þ transition electric
dipole moment and the permanent electric quadrupole moment a of N 2 (H= 1.5
10
−26
esu) can be strong in these case if the E,v E and D,v D vibronic levels are
near-resonant (R is the distance between centers of mass of the colliding partners).
The EP channel (6.3.23) has to prevail in this case (see Sect. 5.3.2.5 in [18]).
Besides, dispersion, * R
−6 , interaction has to be strong for all, M = Ar, Kr, N 2 ,
partners due to huge dipole moment of the I 2 ðE0
þ
g À D0
þ
u Þ transition, l E-D % 25
10
−18
esu and, hence, giant polarizability a I 2 E
ð Þ % 2 Á 10
5 ˚
A
3 of the I 2 (E) state.
Binding energies of the complex have to be proportional to the l EÀD
j
j
2 a M products,
a M = 1.64 (Ar), 1.77 (N 2 ), 2.48 (Kr), units, Å
3 , are polarizabilities of the partners
(see above and Fig. 6.32).
One sees, that dispersion interaction prevails in the N 2 I 2 (E,v E ,n E ) complexes
since:
the EP channel (6.3.23) has very low probability,
the N 2 I 2 (E,v E ,n E ) binding energy is larger than that of ArI 2 (E,v E ,n E ) and less than
KrI 2 (E,v E ,n E ).
To examine in what N 2 I 2 isomer transitions in the complex occur, calculation of
the N 2 I 2 (X) PES taking into account its linear, parallel, T-shaped and trapezoidal
isomers. It was shown that the parallel N 2 I 2 (E) isomer is observed in the experiments, probably. The low energy barrier between trapezoidal and parallel isomers
results in free rotor vibrational state. Both C 2v and C s symmetry are realized, so EP
channels (3.6.21, 3.6.22) are allowed.
6.4 Rare Gas-Halogen Molecule Clusters
6.4.1 Rg
1
x Rg
2
y I 2 Clusters
The first studies of the weakly-bound clusters were carried out by D.H. Levy and
coworkers [103, 125, 127, 128]. It was shown, in particular, that there are blue
shifts in excitation spectra of VP product luminescence
Ne x He y I 2 B; v B
X; 0
ð
Þ ;
ð6:4:1Þ
m – m 0 % 6.25x + 3.67y (cm
−1 ), x
4, y
4, v B = 13–26 [103]
Ar x He y I 2 B; v B
X; 0
ð
Þ ;
ð6:4:2Þ
m– m 0 % 13.5x + 3.8y (cm
−1 ), x
3, y
2, v B = 21, 22 [128] clusters. Here, m
is a wavenumber of the excitation band maximum, and m 0 is a wavenumber of the
6.3 Van der Waals Complexes
251