This thesis presents the results of two experiments that measure
the
evolution of laser excited molecules. The experiment performed
with 0.1-ps
laser pulses elucidates the dynamics of desorption of O2
and formation of
CO2 on a platinum surface. The experiment
performed with nanosecond time
resolution reveals the inter- and intra- molecular vibrational
dynamics of
infrared laser pumped molecules.
Desorption of O2 and formation of CO2 were induced with
subpicosecond laser pulses on a Pt(111) surface dosed with
coadsorbed O2
and CO. Fluence dependent yields obtained over a range of laser
wavelengths
from 267 to 800 nm, and pulse durations from 80 fs to 3.6 ps are
presented.
We observe a dependence of the nonlinear desorption yield on
wavelength.
Two-pulse correlation measurements show two different time-
scales relevant
to the desorption. The results show that nonthermal electrons play
a role in
the surface chemistry, and that an equilibrated pre-heating of the
surface
modes leads to enhanced desorption.
In the second set of experiments reported in this thesis, time-
resolved
coherent anti-Stokes Raman spectroscopy was used to obtain the
rovibrational energy distributions in polyatomic molecules
following infrared
multiphoton excitation. In addition to presenting new results on
SF6, we
review previously obtained data on SO2 and OCS.
The data yield new details
about infrared multiphoton excitation and intramolecular
vibrational energy
relaxation. In particular they show the significance of collisions in
redistributing vibrational energy following excitation. The results
also clearly
show stronger inter-mode coupling and higher excitation in
systems with
increasing numbers of atoms per molecule.
In addition, a detailed description is provided of the
Ti:Sapphire based
ultrashort pulsed amplified laser system. Both, the principles and
the design
of the laser system are discussed to serve as a manual for the
femtosecond
laser system constructed for the study of molecules adsorbed on a
metal
surface.
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