Molecular physics in Bergen and Iceland (updated 290411; 14:30 o´clock):
1) Two color experiment (i.e. UV(ns) + IR(fs) REMPI studies)
2) Theoretical interpretations(?) (being constructed)
In the following is a (pictorial) presentation of the up to date status / plan for
1) -a “Two color experiment” to be performed in Bergen and
2) – a theoretical interpretations which would be highly useful support for the
experiments(?)(being constructed)
1) Two color experiment (i.e. UV(ns) + IR(fs) REMPI studies)
The plan is to perform a three- (or two-) photon resonance excitation (UV(ns)) of a molecule
(HX; X= Cl or Br) to a Rydberg state followed by a two-photon ionization to form HX+ + e(IR(fs)) and to detect HX+ with an ion detector (channeltron). This will be performed for
resonance excitations to
a) -a “long lived” quantum state1).
b) -a “shorter lived” quantum state 1).
Fig. 1 shows schematic figure for the experimental setup.
Figs. 2 (a) and (b) show an example for the energetics for the two resonance excitations (a)
and (b) mentioned above.
Figs. 3 (a) and (b) shows expected HCl+ signals for cases (a) and (b) from dye laser pulse
excitation
Fig. 4 shows expected ion-signal vs. several fs laser pulse sequences.
The second harmonic of the Nd:Yag laser (532 nm) will be used (for three-photon excitation).
The Nd:Yag-dye laser system will operate in 14 Hz pulse repetition (8 ns wide laser pules).
The HX gas will be inserted into the excitation region via pulsed nozzle from a gas cylinder.
The nozzle opening frequency and the dye laser repetion rate need to be synchronized. The
femtosecond laser will operate in 80 MHz pulse repetition (150 fs wide pulses)
unsynchronized(?)2). The second colour (IR(fs)) excitation should only form molecular ions
(HX+) and no (or negligible) fragment ions (“atom ions”) since formation of H+ and X+ will
require a lot more energy (see fig. 2). The lifetimes of the two different resonance excitated
states (a) and (b) are expected to differ, the lifetime of (a) being dominantly(?) determined by
fluoresecence whereas the lifetime of (b) will be determine by dissociation via interaction
with an ion-pair state as well as fluorescence (see Fig. 3). Ion signal measurements for (a) and
(b) for n dye laser pulses will reflect the different decay curves for the two excited states (a)
and (b).
References/notes:
1) choose of states is based on results from REMPI-TOF analysis perfomed in Iceland
(see: http://notendur.hi.is/agust/rannsoknir/Bergen/XLS-060411ak.xls)
2) NB: Will it be possible to trigger the fs laser by the dye laser (synchronize the dye
and the fs laser) so that reproducable sequences of fs pulses will be obtained (see
fig. 4)?
To
diffusion
pump
channeltron
UV(ns)
Pulsed nozzle;
General valve
Molecular
“beam”
IR(fs)
valve
HX
gas
bottle
To
pump
Fig. 1: Schematic figure for the experimental setup (agust,heima,....2011/equipments-280411ak.ppt)
145438.14 cm-1
...H+ + Cl + e- ......
...H+ Cl+ + e- ......
140
140750.4 cm-1
(b)
(a)
120
.....HCl+ + e- ......
Energy/
cm-1
100
102819 cm-1
IR
(fs)
IR
(fs)
Rydb.
J´=5
80
82079.82
cm-1
x10
3
82338.14
cm-1
Rydb.
J´=2
Dissociation
via an Ion-pair
state
60
fluoresc.
 ~ 10 ns(?)
40
fluoresc.
 ~ 10 ns(?)
UV
(ns)
UV
(ns)
20
J´´=5
0
312.74 cm-1
J´´=2
62.62 cm-1
Fig. 2. Example for resonance excitations (a) and (b): The example corresponds to threephoton resonance excitation to the 32, v´=0 state of HCl. (<= agust,heima,...2011/PPT-28041aak.ppt)
HCl+
signal
UV
(ns) (a)
UV
(ns)
 exp(--1*t)
 exp(-(-1+d-1)*t)
J´´=5
J´´=2
312.74 cm-1
62.62 cm-1



(b)
Fig. 3 Expected HCl+ signals for cases (a) and (b) from dye laser pulse excitation.
 exp(--1*t)
J´´=5
312.74 cm-1


J´´=2
62.62 cm-1

IR(fs)
pulses
Fig. 4 Expected ion-signal from dye laser pules excitation vs. several fs laser pulse sequences
(80 MHz repetition rate / with 12. 5 ns time intervals between pulses)