Molecular physics in Bergen and Iceland:
HCl/HBr Lifetimes and lifetime measurements for Rydberg states
The following statement, taken from
“ http://www.springerlink.com/content/xrr70m3461371160/ ”
-tells a lot about
1) reasons for interests in molecular Rydberg states and
2) problems with Rydberg states
“The reactivity of Rydberg states is of interest due to their large radius (1) but the
practical use of them is limited by their rapid decays by predissociation(2).”
i.e. it is generally believed that the lifetimes of Rydberg states are short (on the picosecond
time scale) due to indirect dissociation (e.g. predissociation) such as case (b) in Fig. 1 below
(also shown in older e-mail:280411/
http://www3.hi.is/~agust/rannsoknir/Bergen/Molecular%20physics-Bergen.doc ). Our idea,
as mentioned earlier, however, is that indirect dissociation via ion-pair states is quantum level
dependent, i.e. cases (a) or (b) in fig. 1 and by choosing case (a) we can avoid such
dissociation channels, BUT there could be additional predissociation channels, such as i)
direct predissociation due to a transfer from the Rydberg state to a repulsive state, which
would depend on the transition probability or ii) indirect predissociation via gateway
Rydberg states which could couple to “our Rydberg state” by spin-orbit coupling (see for
example http://www3.hi.is/~agust/rannsoknir/papers/jcp131-044324-09.pdf ), in which case
(a) in fig 1 becomes (a2) shown in fig. 2 and the lifetime of “our Rydberg state” could be
significantly shorter than the lifetime due to fluorescence only (ca. 10 ns) . This we do not
know and there are very limited lifetime measurements for HCl(HBr) Rydberg states
available in the literature. Fluorescence measurements is the standard way to perform lifetime
determinations. I have found no such data for HCl and HBr(?). The only lifetime estimates,
which I have found, are based on spectra bandwidths which simply give crude lower limit
values. It might, however, be possible to avoid excitations to Rydberg states which i) undergo direct predissociation and /or ii) -indirect predissociation in our experiments, but the
bottom line is that there is a large uncertainty concerning what the lifetimes are. These
could be as low as, say 10 ps or as high as 10 ns and most probably these will vary a lot
depending on states and quantum levels which we choose to excite. If, on the other hand we
succeed to do lifetime measurement by a new technique, as planed by Jana et al., it could be a
major step forward and big contribution to important questions asked concerning molecular
Rydberg states and, of course, finding long lived Rydberg states would be of great interest.
Updated: 040511; agust,heima,...Molecular physics-030511ak.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
Fig. 1
312.74 cm-1
J´´=2
62.62 cm-1
145438.14 cm-1
...H+ + Cl + e- ......
...H+ Cl+ + e- ......
140
140750.4 cm-1
(a2)
120
.....HCl+ + e- ......
100
102819 cm-1
Energy/
cm-1
IR
(fs)
3
80
Gateway
state
Rydb.
J´=5
(ii)
82338.14
cm-1
x10
(i)
 = ? ps
H + Cl
60
fluoresc.
 ~ 10 ns(?)
40
UV
(ns)
20
J´´=5
0
Fig. 2
312.74 cm-1