Polyyne molecules were produced as a result of the femtosecond laser irradiation of
liquid acetone (CH3)2CO and alkane molecules hexane C6H14 and octane C8H18 using
800 nm, 100 fs duration pulses. These polyynes have been detected as a Raman band
in irradiated liquid from 1800 to 2200 cm−1. Polyyne molecules generally detected as
a Raman band in SERS experiment are C8H2, C10H2, C12H2 and C14H2. Two well
established experimental techniques, time of flight mass spectrometry and surface
enhanced Raman spectrometry were used to identify positively polyyne formation as
a result of femtosecond laser irradiation of acetone and alkane liquids. Small polyynes
C2H2, C4H2, and C6H2 were positively detected in the time of flight mass spectrometer
TFMS, while longer polyynes from C6H2, C8H2, C10H2, C12H2 and C14H2 were detected
by surface enhanced Raman spectroscopy SERS.
Intensity capping occurs in a liquid due to filamentation, and the resulting intensity
in a liquid is s 1013 W/cm2 during irradiation. This results in main process of
ionization in the larger part of the laser focus as multiphoton ionization MPI. Focal
volume increase in a liquid provides a larger volume where ions C+, C+2 and C2+are
produced to initiate chemical reactions outside the laser focus.
The current work established positively, that the longer polyyne formation does
not occur by dehydrogenation of alkane molecules by only breaking the C-H bonds as
was previously anticipated. It is proposed in this work that lengthening of polyyne
chains occurs due to addition reaction of species of C+, C+2 and C2+ to double bonded
species themselves produced as a result of the breaking down of the parent molecules
in the laser focus. The carbon addition reactions occur outside the laser focus due to
the close proximity of molecules in the liquid phase.
| Identifer | oai:union.ndltd.org:WATERLOO/oai:uwspace.uwaterloo.ca:10012/5585 |
| Date | January 2010 |
| Creators | Zaidi, Asif Ali |
| Source Sets | University of Waterloo Electronic Theses Repository |
| Language | English |
| Detected Language | English |
| Type | Thesis or Dissertation |
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