– The pump-probe method when RgHal 2 (B, v B ) complex vibrational predissociation (VP) products, e.g., produced due to absorption of a pump laser photon by
a complex are excited to the gerade (g) ion-pair (IP) states, Hal 2 ðE0
þ
g Þ, for
example, and luminescence of this IP state are monitored during measurement
of excitation spectra. Action spectra can also be measured: wavelength of probe
radiation is fixed and that of pump radiation scan;
– Luminescence depletion techniques. The two dye laser beams are
counter-propagated through the jet expansion chamber and spatially overlapped.
The depletion laser is fired before the probe laser, and depopulate the lower vdW
state from which the transition studied occurs. Therefore, this transition is
depleted (see [33] for details);
– Velocity-map imaging method. A supersonic molecular beam is produced by
pulsed supersonic jet expansion generated by a pulse valve into a source
chamber evacuated with high pumping speed. A central part of the gas jet passes
through a skimmer into an electrostatic lens chamber where it crosses with a
focused pulse laser beam. The energy of the laser pulse has to be enough to
excite ground state molecule to Rydberg state and then ionize it in the (2 + 1)
schemes. Ions produced at the laser beam spot are extracted by a three-electrode
electrostatic lens to time-of-flight (TOF) tube. After passing it, ions hit an
imaging detector consisting of a microchannel plate and phosphor screen. A 2D
image of the phosphor screen is recorded by a charge-coupled device. The ring
structures in the VMI images reflect the distribution of the ions as a function of
kinetic energy. The sum of the kinetic energies of the fragment ions formed in
the dissociation or predissociation processes is termed as Kinetic Energy
Release (KER). Analysis of the KER spectra allows assigning the channels of
Rydberg state predissociation (see Sect. 2.8 in [18]).
A large amount of experimental and theoretical data have been obtained, and
spectroscopic characteristics of the RgX 2 (X, B) and RgXY(X, B, A) states and the
complex electronically-excited states dynamics are studied. Three conformers of
RgX 2 complexes have been observed and studied. These are T-shaped (C 2v symmetry group), linear (C 1v symmetry group) RgX 2 (X, B) complexes which vibrational wave functions are localized at H = 90°, 0 and 180°, respectively, as well as
‘free-rotor’ or bending complexes which vibrational wave functions are delocalized
over H = 0–360° (Fig. 6.1).
The vast majority of works are devoted to the research of the RgX 2 and RgXY
ground states. As to excited valence states, there are experimental and theoretical
data on the I-containing, RgI 2 (B), and, to a lesser extent, RgXY(B, A) states (see
Sects. 6.3.2 and 6.3.3). As to RgI 2 (IP) and RgXY(IP) complexes, to the best of the
author’s knowledge, six works devoted to the HeICl(E0
+
, b1) [28], NeICl(E, b)
[34–36] and HeI 2 (E) [37, 38] had been published up to 2016, when the first paper
on the RgI 2 (E) complexes was published by the author’s team [39].
As it has been mentioned in Sect. 6.1, in this chapter, we consider only those
weakly bound complexes that are weakly bound in electronically excited states, as
well. An analysis of the papers, mentioned in [22, 40] shows that the RgMe,
6.3 Van der Waals Complexes
203
a complex are excited to the gerade (g) ion-pair (IP) states, Hal 2 ðE0
þ
g Þ, for
example, and luminescence of this IP state are monitored during measurement
of excitation spectra. Action spectra can also be measured: wavelength of probe
radiation is fixed and that of pump radiation scan;
– Luminescence depletion techniques. The two dye laser beams are
counter-propagated through the jet expansion chamber and spatially overlapped.
The depletion laser is fired before the probe laser, and depopulate the lower vdW
state from which the transition studied occurs. Therefore, this transition is
depleted (see [33] for details);
– Velocity-map imaging method. A supersonic molecular beam is produced by
pulsed supersonic jet expansion generated by a pulse valve into a source
chamber evacuated with high pumping speed. A central part of the gas jet passes
through a skimmer into an electrostatic lens chamber where it crosses with a
focused pulse laser beam. The energy of the laser pulse has to be enough to
excite ground state molecule to Rydberg state and then ionize it in the (2 + 1)
schemes. Ions produced at the laser beam spot are extracted by a three-electrode
electrostatic lens to time-of-flight (TOF) tube. After passing it, ions hit an
imaging detector consisting of a microchannel plate and phosphor screen. A 2D
image of the phosphor screen is recorded by a charge-coupled device. The ring
structures in the VMI images reflect the distribution of the ions as a function of
kinetic energy. The sum of the kinetic energies of the fragment ions formed in
the dissociation or predissociation processes is termed as Kinetic Energy
Release (KER). Analysis of the KER spectra allows assigning the channels of
Rydberg state predissociation (see Sect. 2.8 in [18]).
A large amount of experimental and theoretical data have been obtained, and
spectroscopic characteristics of the RgX 2 (X, B) and RgXY(X, B, A) states and the
complex electronically-excited states dynamics are studied. Three conformers of
RgX 2 complexes have been observed and studied. These are T-shaped (C 2v symmetry group), linear (C 1v symmetry group) RgX 2 (X, B) complexes which vibrational wave functions are localized at H = 90°, 0 and 180°, respectively, as well as
‘free-rotor’ or bending complexes which vibrational wave functions are delocalized
over H = 0–360° (Fig. 6.1).
The vast majority of works are devoted to the research of the RgX 2 and RgXY
ground states. As to excited valence states, there are experimental and theoretical
data on the I-containing, RgI 2 (B), and, to a lesser extent, RgXY(B, A) states (see
Sects. 6.3.2 and 6.3.3). As to RgI 2 (IP) and RgXY(IP) complexes, to the best of the
author’s knowledge, six works devoted to the HeICl(E0
+
, b1) [28], NeICl(E, b)
[34–36] and HeI 2 (E) [37, 38] had been published up to 2016, when the first paper
on the RgI 2 (E) complexes was published by the author’s team [39].
As it has been mentioned in Sect. 6.1, in this chapter, we consider only those
weakly bound complexes that are weakly bound in electronically excited states, as
well. An analysis of the papers, mentioned in [22, 40] shows that the RgMe,
6.3 Van der Waals Complexes
203