Photolysis is a chemical process where molecules are broken down by light absorption. Flash photolysis is commonly used to study short-lived intermediates in photochemical reactions, employing a photolysis flash to initiate reactions followed by a monitoring flash to measure absorption spectra. To study processes in the nanosecond time range, lasers can be used to generate photolysis pulses less than 20 nanoseconds, allowing observation of excited singlet state lifetimes and other fast reactions. Laser flash photolysis systems employ a laser pulse to synchronize a photolysis spark and provide pulses to initiate reactions and monitor absorption on nanosecond timescales, enabling identification of transient intermediates and insight into fast reaction mechanisms.

2.  Photolysis, chemical process by which molecules
are broken down into smaller units through the
absorption of light.

3.  The best-known example of a photolytic process
is the experimental technique known as flash
photolysis, employed in the study of short-lived
chemical intermediates formed in many
photochemical reactions .

4.  There is much to be gained by extending the flash
photolysis technique into the nanosecond region.
Excited singlet states of organic molecules and
singlet exactions in molecular crystals have
lifetimes in the nanosecond range.The chemistry
of the solvated electron following pulse radiolysis
has been widely studied in the past few years,
recently on the nanosecond time scale.

5.  FLASH PHOTOLYSIS
 LASER FLASH PHOTOLYSIS

6.  Flash photolysis is a commonly used fast reaction
technique for photochemical reactions. For
reactions with a moderate rate, flash lamps
provide sufficient time response.
 To maintain nanosecond range flash photolysis
technique is used.

7.  The flash photolysis system can perform transient
absorption measurements within the short
nanosecond range. The absorption spectrum of
the formation and decay process of intermediaries
in photoreactions such as photo dissociation,
photoisomerization reaction, etc can be observed.
Due to the newly developed software added with
the adoption of the optics, transient absorption
spectrum measurements in the nanosecond range
have been made easier.

8. THE conventional flash photolysis technique is limited,
by the flash duration, to times which are usually greater
than 1 µs . There is a need to reach times shorter than
this, particularly to observe and study the absorption of
excited singlet states which typically have lifetimes in the
nanosecond range. The appearance of the Q switched
laser has provided a means to this end, and photo
electronic detection methods have already been used in
several laboratories to observe transients in the
nanosecond region.

9. LASERT FLASH PHOTOLYSISLASERT FLASH PHOTOLYSIS
SPECTROMETERSPECTROMETER

10.  The principal components of a flash photolysis
apparatus, apart from a spectrograph or
monochromator, are an initiating photolysis flash
source, a monitoring flash source, a -unit which
introduces a delay between these two flashes
and, for subsequent kinetic work at selected
wavelengths, a monitoring source with
photoelectric detection system. The substantial
changes which have been made in each of these
components

11. In order that useful information may be derived
from a flash photolysis experimnent, it is usually
necessary that the photolytic and monitoring
pulses be of shorter duration than the processes to
be studied. For nanosecond events, the giant-
pulsed laser provides a means of generation of a
burst of ultraviolet radiation sufficiently energetic
for the purposes of flash photolysis, of duration
less than or equal to 20ns.

12. The principle of flash photolysis. A gas mixture flows into the reaction vessel,
and reactions are initiated by a burst of intense radiation from a flash lamp.
A second flash lamp acts as a source for measurement of the absorption spectrum
of the resultant gas mixture.

13.  A great advantage of the laser photolysis
technique is that the laser pulse and the
breakdown spark the automatically synchronized
to within a few nanoseconds because they
originate from the same primary laser pulse. No
electronic circuitry is needed other than that
required for operating the laser.

14.  Its applications to the observation of the
absorption spectra of excited singlet states, short-
lived excited triplet states and chemical events in
the nanosecond time region are described.
 The method is a valuable tool for the identification
of transient chemical intermediates and hence for
the study of mechanisms of fast chemical
reactions

15.  During photolysis reaction reactions can be
proceed in very short time like in nanoseconds.