Transcript Electronic and Photoelectron Spectroscopy of Toluene_1.pptx

Electronic and Photoelectron
Spectroscopy of Toluene
Adrian M. Gardner, Alistair M. Green, Victor M. Tamé-Reyes,
Victoria H. K Wilton and Timothy G. Wright
67th International Symposium on Molecular Spectroscopy
Ohio State University
19th June 2012
Introduction: Vibrational Modes
• Often, vibrations are considered in the harmonic approximation.
• Within this approximation normal vibrational modes are
considered to be independent.
• However, true vibrational eigenstates are a linear combination of the
harmonic levels.
Introduction: Aims
• Many vibrational levels in the S1 electronic state of toluene-h8 have been
assigned by Hickman et al.1
• This was achieved by recording dispersed fluorescence spectra via many
of the observed S1 vibrational levels.
• In the present investigation we aim to gain information on the toluene
cation by employing 1+1′ Zero Kinetic Energy (ZEKE) photoelectron
spectroscopy.
• We also study the toluene-d3 isotopologue in order to investigate the
effects of the small isotopic shifts of vibrational frequencies on the
appearance of electronic and photoelectron spectra of like molecules.
1. C. G. Hickman, J. R. Gascooke and W. D. Lawrance, J. Chem. Phys., 104, 4887 (1995).
REMPI Spectra
Toluene-h8
Toluene-d3
• Qualitatively, the two spectra are very similar.
• An intense feature, assigned to the M291 vibration, dominates this
wavenumber range.
• The relatively weak S1 origin band is an effect of low UV intensity.
ZEKE Spectra via a Fermi Resonance
Toluene-h8
Toluene-d3
•
Hickman et al.1 previously assigned the bands labelled B and C as a Fermi
Resonance between the M111 and M191M201 vibrations.
•
Davies et al.2 later proved the presence of a third coupled vibration in this Fermi
Resonance, assigned M142 in the present nomenclature.
x2
+
1. C. G. Hickman, J. R. Gascooke and W. D. Lawrance, J. Chem. Phys., 104, 4887 (1995).
2. J. A. Davies, A. M Green and K. L. Reid, PCCP, 12, 9872 (2010).
ZEKE Spectra via a Fermi Resonance
Toluene-h8
Toluene-d3
ZEKE Spectra via a Fermi Resonance
Toluene-h8
Toluene-d3
ZEKE Spectra via a Fermi Resonance
Toluene-h8
Toluene-d3
ZEKE Spectra via a Fermi Resonance
Toluene-h8
Toluene-d3
ZEKE Spectra via a Fermi Resonance
Toluene-h8
Toluene-d3
Intramolcular Vibrational Energy
Redistribution
• Hickman et al.1 assigned the two bands, denoted
I and J, as a Fermi Resonance between the
M181M191 and M101 vibrations.
Intramolcular Vibrational Energy
Redistribution
• Hickman et al.1 assigned the two vibrations,
denoted I and J, as a Fermi Resonance between
the M181M191 and M101 vibrations.
• The ZEKE spectra recorded via these two levels
show a broad, noisy “hump”, a signature of IVR.
• Similar observations are made in the DF
recorded via these intermediate levels.
1. C. G. Hickman, J. R. Gascooke and W. D. Lawrance, J. Chem. Phys., 104, 4887 (1995).
Intramolecular Vibrational Energy
Redistribution
• Hickman et al.1 assigned the two vibrations,
denoted I and J, as a Fermi Resonance between
the M181M191 and M101 vibrations.
• The ZEKE spectra recorded via these two levels
show a broad, noisy “hump”, a signature of IVR.
• Similar observations are made in the DF
recorded via these intermediate levels.
Varsányi3 mode 1
1. C. G. Hickman, J. R. Gascooke and W. D. Lawrance, J. Chem. Phys., 104, 4887 (1995).
3. G. Varsányi , Assignments of the Vibrational Spectra of Seven Hundred Benzene Derivatives, (Wiley, New
aaaaYork, 1974) Vol. 2.
Intramolecular Vibrational Energy
Redistribution
• Similarly, the dispersed fluorescence spectra,1
and ZEKE spectra recorded via L show a broad,
noisy “hump”.
• This intermediate level was assigned to the M61
vibration by observation of this band in the DF
spectrum– also observed in the ZEKE spectrum.
• As in the M101 vibration, this mode contains significant C-CH3 stretching character – a
possible mechanism for the acceleration of IVR?
1. C. G. Hickman, J. R. Gascooke and W. D. Lawrance, J. Chem. Phys., 104, 4887 (1995).
Conclusions
• REMPI and ZEKE spectra recorded for toluene-h8 and toluene-d3 have
been presented.
• The spectra for each isotopologue are qualitatively very similar; however
the small shifts in vibrational frequency upon deuteration result in
changes in the appearance of the spectra.
• Evidence for IVR has been observed in spectra recorded via low frequency
S1 intermediate levels.
• In these instances, the vibrational modes involve contain significant
stretching C-CH3 motion.
Acknowledgements
Professor Timothy Wright
Dr Alistair Green
Victor Tamé-Reyes
Victoria Wilton
Professor Katharine Reid
Dr Julia Davies
Experimental Apparatus