intermolecular interactions are polarization (induction and dispersion interactions,
see Sects. 6.3.3, 6.3.4 as well as Sects. 5.3.2 and 6.4 in [18]).
The population and decay of vdW complexes in the gas phase play a fundamental role in the kinetics and dynamics of electronically-excited molecular states.
They are responsible for radiative emission and energy transfer in the atmosphere,
energy pooling and conversion in laser media, relaxation phenomena in chemiluminescence processes, plasma formation, and in many other situations, where
electronically-excited states are involved. The description of these processes is
significant for understanding the mechanisms of non-adiabatic transitions in
weakly-bound complexes and clusters. An understanding of population and decay
of vdW complexes is also essential for an interpretation and a modeling of various
photoinitiated processes in liquids and solids, where the role of intermolecular
interaction is greatly magnified through the formation of solvation shell(s) and
multiple collisions between a molecule and a solvent. One should note that decay of
vdW complexes has much in common with vibrational relaxation and electronic
predissociation induced by collisions with atoms and molecules, which have been
discussed in Chap. 3.
An energy of a vdW bond is small, less than several hundred cm
−1 (see below).
Therefore, to observe and study vdW complexes, it is required cooling atoms or
molecules to sufficiently low temperatures by utilizing the supersonic molecular
beam technique (see Sect. 6.2 in [18]).
The first pioneering work devoted to studies vdW complexes in
electronically-excited states using the supersonic molecular beam was published in
1976 by D. H. Levy and his team [19]. Heretofore, rotational constants of the RgHX
(X, v x = 0) and ROCS(X, v x = 0) by means of molecular beam electric resonance
spectroscopy were determined by W. Klemperer’s team (see [20, 21] and references as
well as [22]). This field of chemical physics and molecular spectroscopy is trendy at
present. One of the most thoroughly studied groups of vdW complexes are complexes
consisting of homonuclear halogens (hereafter, X 2 ) or interhalogens (XY) and rare gas
atoms, RgX 2 ðX0
þ
g ; B0
þ
u ; E0
þ
g Þ, RgXY(X0
+
, B0
+
, A1, E0
+ , b1, D'2 ). Decades of
experimental and theoretical papers devoted to vdW complexes have been published
(see [23–31] and references). Bound excited X 2 , XY valence states are perturbed by
repulsive states (see Sect. 4.2.3 and Fig. 4.4), and predissociation of the complexes to
Rg and halogen atoms occurs. Therefore, the only methods of studies spectroscopic
characteristics and dynamics of these complexes at the supersonic molecular bands
are the following (see Sect. 6.2 in [18]):
– Intracavity laser spectroscopy. Supersonic jet is placed within the optical resonator cavity of an amplitude modulated cw dye laser. The laser output was
dispersed with a spectrometer. Absorption features appear as
wavelength-dependent losses in the spectral profile of the laser output (see [32]
and references for details);
– Measurements of luminescence spectra of halogens (interhalogens) which are
the products of vibrational predissociation of the complexes; a loss of several
vibrational quanta can occur in these processes;
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6 Weakly-Bound Complexes and Clusters
see Sects. 6.3.3, 6.3.4 as well as Sects. 5.3.2 and 6.4 in [18]).
The population and decay of vdW complexes in the gas phase play a fundamental role in the kinetics and dynamics of electronically-excited molecular states.
They are responsible for radiative emission and energy transfer in the atmosphere,
energy pooling and conversion in laser media, relaxation phenomena in chemiluminescence processes, plasma formation, and in many other situations, where
electronically-excited states are involved. The description of these processes is
significant for understanding the mechanisms of non-adiabatic transitions in
weakly-bound complexes and clusters. An understanding of population and decay
of vdW complexes is also essential for an interpretation and a modeling of various
photoinitiated processes in liquids and solids, where the role of intermolecular
interaction is greatly magnified through the formation of solvation shell(s) and
multiple collisions between a molecule and a solvent. One should note that decay of
vdW complexes has much in common with vibrational relaxation and electronic
predissociation induced by collisions with atoms and molecules, which have been
discussed in Chap. 3.
An energy of a vdW bond is small, less than several hundred cm
−1 (see below).
Therefore, to observe and study vdW complexes, it is required cooling atoms or
molecules to sufficiently low temperatures by utilizing the supersonic molecular
beam technique (see Sect. 6.2 in [18]).
The first pioneering work devoted to studies vdW complexes in
electronically-excited states using the supersonic molecular beam was published in
1976 by D. H. Levy and his team [19]. Heretofore, rotational constants of the RgHX
(X, v x = 0) and ROCS(X, v x = 0) by means of molecular beam electric resonance
spectroscopy were determined by W. Klemperer’s team (see [20, 21] and references as
well as [22]). This field of chemical physics and molecular spectroscopy is trendy at
present. One of the most thoroughly studied groups of vdW complexes are complexes
consisting of homonuclear halogens (hereafter, X 2 ) or interhalogens (XY) and rare gas
atoms, RgX 2 ðX0
þ
g ; B0
þ
u ; E0
þ
g Þ, RgXY(X0
+
, B0
+
, A1, E0
+ , b1, D'2 ). Decades of
experimental and theoretical papers devoted to vdW complexes have been published
(see [23–31] and references). Bound excited X 2 , XY valence states are perturbed by
repulsive states (see Sect. 4.2.3 and Fig. 4.4), and predissociation of the complexes to
Rg and halogen atoms occurs. Therefore, the only methods of studies spectroscopic
characteristics and dynamics of these complexes at the supersonic molecular bands
are the following (see Sect. 6.2 in [18]):
– Intracavity laser spectroscopy. Supersonic jet is placed within the optical resonator cavity of an amplitude modulated cw dye laser. The laser output was
dispersed with a spectrometer. Absorption features appear as
wavelength-dependent losses in the spectral profile of the laser output (see [32]
and references for details);
– Measurements of luminescence spectra of halogens (interhalogens) which are
the products of vibrational predissociation of the complexes; a loss of several
vibrational quanta can occur in these processes;
202
6 Weakly-Bound Complexes and Clusters