adrian m. gardner, alistair m. green, victor m. tamé-reyes, victoria h. k wilton and timothy g....

Adrian M. Gardner, Alistair M. Green, Victor M. Tamé-Reyes, Victoria H. K Wilton and Timothy G. Wright

Electronic and Photoelectron Spectroscopy of Toluene

67th International Symposium on Molecular SpectroscopyOhio 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.

Toluene-h8 Toluene-d3

ZEKE Spectra via a Fermi Resonance

• Hickman et al.1 previously assigned the bands labelled B and C as a Fermi Resonance between the M11

1 and M191M20

1 vibrations.

• Davies et al.2 later proved the presence of a third coupled vibration in this Fermi Resonance, assigned M14

2 in the present nomenclature.

x2 +


2. J. A. Davies, A. M Green and K. L. Reid, PCCP, 12, 9872 (2010).

Toluene-h8 Toluene-d3

ZEKE Spectra via a Fermi Resonance

Intramolcular Vibrational Energy Redistribution

• Hickman et al.1 assigned the two bands, denoted I and J, as a Fermi Resonance between the M18

1M191 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 M18

1M191 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.


Intramolecular Vibrational Energy Redistribution

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.

Varsányi3 mode 1

• Hickman et al.1 assigned the two vibrations, denoted I and J, as a Fermi Resonance between the M18

1M191 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.

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 M6

1 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?


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.

Professor Timothy WrightDr Alistair GreenVictor Tamé-ReyesVictoria Wilton

Professor Katharine ReidDr Julia Davies

Acknowledgements

Experimental Apparatus

adrian m. gardner, alistair m. green, victor m. tamé-reyes, victoria h. k wilton and timothy g....

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