Dv B > 2, VP product becomes much more important. For v B = 21, both NeBr 2 (B,
v B -1 and v B -2) intermediates have been observed. These intermediates have significantly different kinetics, with the NeBr 2 (B, v B -1) decay rate nearly twice that of
the NeBr 2 (B, v B -2). Both Br 2 (B, v B -2) and Br 2 (B, v B -3) VP products are formed in
almost equal amounts, but the Br 2 (B, v B -2) product formation rate is faster than that
of Br 2 (B, v B -3). The broad vibrational product state distributions and multiple
dissociation pathways indicate that IVR becomes increasingly important for v B > 19.
6.4.2.2 The Rg 2 Cl 2 Clusters
The Ar 2 Cl 2 Clusters. Ar 2 Cl 2 (X) cluster is a distorted tetrahedron with an Ar 2 -Cl 2
distance of 3.9(5) Å and an Ar–Ar bond distance of 4.1(6) Å. The binding energy of
the Ar 2 Cl 2 (X) cluster is 447.5 ± 3.5 cm
−1 , and that of Ar 2 Cl 2 (B, 9) state
is *426 cm
−1 . Three Cl 2 (B, v B ) vibrational quanta are necessary for the Ar 2 Cl 2 (B,
9) VP [134].
The Ne 2 Cl 2 Clusters. The structure of the Ne 2 Cl 2 (X) state, as well as the structure
and dynamics of Ne 2 Cl 2 (B) state, have been studied using the laser pump-probe
spectroscopy in [135]. It has been shown that Ne 2 Cl 2 has a distorted tetrahedral
structure in both states with a Ne–Ne bond length of 3.23(5) Å and Ne 2 center of
mass to Cl 2 center of mass distance of 3.12(3) Å. The Ne 2 Cl 2 (B, v B = 7–13) binding
energy is *147 cm
−1 . For the v B < 10 levels, transfer of one Cl 2 (B, v B ) vibrational
quantum to the vdW modes is sufficient to dissociate both neon atoms from the
complex, but the Ne 2 Cl 2 (B, v B − Dv B ) VP occurs via Dv B = 1, as well as the
Dv B = 2 channel. For the Dv B = 2 channel, the NeCl 2 (B) VP product has been
observed. This feature indicates that such a sequential mechanism competes with
the direct Ne 2 Cl 2 (B, v B ) VP. The Ne 2 Cl 2 (B, v B ) lifetime is 123.7, 44.4 and 9.5
(units, ps) for the v B = 8, 11 and 13, respectively.
The He 2 Cl 2 Clusters. The action and excitation spectra of the Cl 2 (E ! B)
luminescence have been measured in [136] to study the VP product state distribution. It has been shown that the Dv B = 2 VP channel is the principal one, and it is
almost certainly a sequential process:
He 2 Cl 2 B; v B
ð
Þ!
#
He þ He 2 Cl 2 B;v B À1
ð
Þ
He þ Cl 2 B;v B À2
ð
Þ
ð6:4:7Þ
The Cl 2 (B, v B ) rotational distribution is remarkably similar to that of HeCl 2 (B,
v B ) observed for the Dv B = 2 channel (see Sect. 6.3.2.2). The authors of [137]
believed that the reason for the similarity was that vibrational excitation of the
HeCl 2 (B, v B ) vdW modes had little effect on the product state distribution. He 2 Cl 2
provides an example of an extremely floppy, liquidlike cluster. The ab initio calculations of the He 2 Cl 2 (X, B) state structures have been carried out also (see [137]
and references).
6.4 Rare Gas-Halogen Molecule Clusters
255
v B -1 and v B -2) intermediates have been observed. These intermediates have significantly different kinetics, with the NeBr 2 (B, v B -1) decay rate nearly twice that of
the NeBr 2 (B, v B -2). Both Br 2 (B, v B -2) and Br 2 (B, v B -3) VP products are formed in
almost equal amounts, but the Br 2 (B, v B -2) product formation rate is faster than that
of Br 2 (B, v B -3). The broad vibrational product state distributions and multiple
dissociation pathways indicate that IVR becomes increasingly important for v B > 19.
6.4.2.2 The Rg 2 Cl 2 Clusters
The Ar 2 Cl 2 Clusters. Ar 2 Cl 2 (X) cluster is a distorted tetrahedron with an Ar 2 -Cl 2
distance of 3.9(5) Å and an Ar–Ar bond distance of 4.1(6) Å. The binding energy of
the Ar 2 Cl 2 (X) cluster is 447.5 ± 3.5 cm
−1 , and that of Ar 2 Cl 2 (B, 9) state
is *426 cm
−1 . Three Cl 2 (B, v B ) vibrational quanta are necessary for the Ar 2 Cl 2 (B,
9) VP [134].
The Ne 2 Cl 2 Clusters. The structure of the Ne 2 Cl 2 (X) state, as well as the structure
and dynamics of Ne 2 Cl 2 (B) state, have been studied using the laser pump-probe
spectroscopy in [135]. It has been shown that Ne 2 Cl 2 has a distorted tetrahedral
structure in both states with a Ne–Ne bond length of 3.23(5) Å and Ne 2 center of
mass to Cl 2 center of mass distance of 3.12(3) Å. The Ne 2 Cl 2 (B, v B = 7–13) binding
energy is *147 cm
−1 . For the v B < 10 levels, transfer of one Cl 2 (B, v B ) vibrational
quantum to the vdW modes is sufficient to dissociate both neon atoms from the
complex, but the Ne 2 Cl 2 (B, v B − Dv B ) VP occurs via Dv B = 1, as well as the
Dv B = 2 channel. For the Dv B = 2 channel, the NeCl 2 (B) VP product has been
observed. This feature indicates that such a sequential mechanism competes with
the direct Ne 2 Cl 2 (B, v B ) VP. The Ne 2 Cl 2 (B, v B ) lifetime is 123.7, 44.4 and 9.5
(units, ps) for the v B = 8, 11 and 13, respectively.
The He 2 Cl 2 Clusters. The action and excitation spectra of the Cl 2 (E ! B)
luminescence have been measured in [136] to study the VP product state distribution. It has been shown that the Dv B = 2 VP channel is the principal one, and it is
almost certainly a sequential process:
He 2 Cl 2 B; v B
ð
Þ!
#
He þ He 2 Cl 2 B;v B À1
ð
Þ
He þ Cl 2 B;v B À2
ð
Þ
ð6:4:7Þ
The Cl 2 (B, v B ) rotational distribution is remarkably similar to that of HeCl 2 (B,
v B ) observed for the Dv B = 2 channel (see Sect. 6.3.2.2). The authors of [137]
believed that the reason for the similarity was that vibrational excitation of the
HeCl 2 (B, v B ) vdW modes had little effect on the product state distribution. He 2 Cl 2
provides an example of an extremely floppy, liquidlike cluster. The ab initio calculations of the He 2 Cl 2 (X, B) state structures have been carried out also (see [137]
and references).
6.4 Rare Gas-Halogen Molecule Clusters
255