Page 99 - High Power Laser Handbook

68 G a s , C h e m i c a l , a n d F r e e - E l e c t r o n L a s e r s Chemical Lasers 69

3.4.3 Deactivation Processes
Deactivation rates in a COIL device’s laser cavity are considerably
slower than HF and DF VT rates. However, because it is difficult to
pressure scale singlet oxygen generators efficiently, it is advantageous
to operate with relatively low-cavity Mach numbers. Furthermore,
the total temperature of delivered SOG flows is low compared with
HF and DF values; thus, even the reduced deactivation rates are an
important concern, primarily because of the need to avoid thermal
choking and to minimize temperature increases.
The most important deactivation processes in the laser cavity
include the following:

*
I + H O → I + H O (3.25)
2
2
*
1
1
I + O ( ∆) → I + O ( ∆) (3.26)
2 2
In addition, considerable losses may be associated with the iodine
dissociation process kinetics and possibly with deactivation by I .
2
3.4.4 Iodine Dissociation
1
O ( ∆) serves the dual function of dissociating the I molecules and
2
2
exciting the I atoms. It is very fortuitous that when molecular iodine
1
is mixed with O ( ∆), it is chemically dissociated, especially because a
2
1
single O ( ∆) lacks the required energy (Fig. 3.22). This behavior was
2
first reported by Ogryzlo and coworkers. Although the dissociation
15
process is not well understood, the original suggestion was that dis-
sociation proceeded via O ( Σ), which was produced by the energy-
1
2
pooling reactions shown in Eq. (3.27), plus the E-E transfer processes
in which some energy loss in excess of the minimum of two O ( ∆)
1
2
molecules is required to dissociate I . However, it is currently believed
2
that iodine dissociation is more complicated than a simple interaction
1
with O ( Σ) and probably involves additional intermediate states that
2
are most probably vibrational in nature.
1
1
1
O ( ∆) + O ( ∆) → O ( Σ) + O ( Σ) (3.27)
3
2 2 2 2
3.4.5 Singlet Oxygen Generator
1
The mechanism for generation of O ( ∆) consists of chlorine absorp-
2
tion in BHP and can be summarized by the net effective reactions that
follow:
+
–
MOH + H O → HO + M + H O, where M = Li, Na, or K (3.28)
2 2 2 2
+
1
–
–
Cl + HO → Ο ( ∆) + 2 Cl + H (rate constant k ) (3.29)
1
2
2
2
–
+
HO + H ↔ Η Ο (3.30)
2 2 2