69 th International Symposium on Molecular Spectroscopy Consistent Assignment of the Vibrations of Monohalosubstituted Benzenes Joe P. Harris, Anna Andrejeva, William D. Tuttle, Timothy G. Wright School of Chemistry, University of Nottingham, UK Igor Pugliesi, Christian Schriever Fakultät für Physik, Ludwig-Maximilians-Universität, München

Notation schemes for substituted benzenes  Introduction - Existing schemes  M notation - Mass trends - G-W Notation  Experiments - Previous studies - Fluorobenzene - Fluorobenzene-d 5  Conclusions - Future work Wilson notation Mulliken notation Varsányi notation Normal modes of molecule labelled with respect to normal modes of benzene Benzene has D 6h symmetry; lowers to C 2v upon substitution Normal modes arranged in symmetry blocks, then by decreasing energy Does not account for energetic re-ordering Loses information on motion of vibrations Subdivides substituents into two classes; ‘heavy’ and ‘light’ Unclear division between the two classes

Gardner-Wright Notation Takes fluorobenzene as a template molecule Applies Mulliken labelling scheme (ie. decreasing energy ordering within symmetry blocks) Treats the target molecule’s substituent as a point mass J Chem Phys (2011)  Introduction - Existing schemes  M notation - Mass trends - G-W Notation  Experiments - Previous studies - Fluorobenzene - Fluorobenzene-d 5  Conclusions - Future work

Mass Trends  Introduction - Existing schemes  M notation - Mass trends - G-W Notation  Experiments - Previous studies - Fluorobenzene - Fluorobenzene-d 5  Conclusions - Future work J Chem Phys (2011) Some mode switching seen for lower masses Mass trends settle down quite quickly Lowest mass atomic substituent would be fluorine x =

Gardner-Wright Notation Takes fluorobenzene as a template molecule Applies Mulliken labelling scheme (ie. decreasing energy ordering within symmetry blocks) Treats the target molecule’s substituent as a point mass J Chem Phys (2011)  Introduction - Existing schemes  M notation - Mass trends - G-W Notation  Experiments - Previous studies - Fluorobenzene - Fluorobenzene-d 5  Conclusions - Future work Uses Duschinsky mixing approach to show correlation between normal modes in different molecules Produces a Duschinsky matrix

Gardner-Wright Notation  Introduction - Existing schemes  M notation - Mass trends - G-W Notation  Experiments - Previous studies - Fluorobenzene - Fluorobenzene-d 5  Conclusions - Future work M 18 and M 19 mix heavily upon excitation ‘True’ Duschinsky Mixing Generalised Duschinsky Mixing

Previous Studies Lipp and Seliskar (1981) J. Mol. Spec., 87, 242 (1981) Vapour-phase absorption FC 6 H 5 and FC 6 D 5 Butler, Moss, Yin, Schmidt, and Kable (2007) J. Chem. Phys., 127, (2007) Laser induced fluorescence and dispersed fluorescence More than 40 DF spectra P ugliesi, Tonge, and Cockett (2008) J. Chem. Phys., 129, (2008) RICC(2) frequency calculations ZEKE spectroscopy  Introduction - Existing schemes  M notation - Mass trends - G-W Notation  Experiments - Previous studies - Fluorobenzene - Fluorobenzene-d 5  Conclusions - Future work

Fluorobenzene-h 5  Introduction - Existing schemes  M notation - Mass trends - G-W Notation  Experiments - Previous studies - Fluorobenzene - Fluorobenzene-d 5  Conclusions - Future work (1 + 1) REMPI

Fluorobenzene-d 5 and -h 5  Introduction - Existing schemes  M notation - Mass trends - G-W Notation  Experiments - Previous studies - Fluorobenzene - Fluorobenzene-d 5  Conclusions - Future work Fluorobenzene-h 5 Fluorobenzene-d 5

 Introduction - Existing schemes  M notation - Mass trends - G-W Notation  Experiments - Previous studies - Fluorobenzene - Fluorobenzene-d 5  Conclusions - Future work Observed position / cm -1 Potential Assignments M 8 M 14 3 M 18 M 16 M 18 M 13 M M 14 M 18 M 30 M M 15 M M 14 M 20 M 29 M 27 M 13 M 17 M 14 M 18 2 M M 7 M 17 M 19 M 14 2 M 29 Observed position / cm -1 Potential Assignments M 16 M 20 M 14 3 M 20 M 17 M M 14 M 20 M M 10 M 14 M 16 M 14 4 Observed position / cm -1 Potential Assignments M 13 M 16 M 18 M 20 M 29 M 13 M 20 M 30 M 13 M M 14 2 M 19 M 20 M 17 M 20 3 M 19 M 20 M 30 M 13 M 14 M 30 M 14 M 18 M 29 M 9 M 12 M 17 M 14 M M 14 M 19 M 30 M 13 M 18 M 20 2

Conclusions  Introduction - Existing schemes  M notation - Mass trends - G-W Notation  Experiments - Previous studies - Fluorobenzene - Fluorobenzene-d 5  Conclusions - Future work

Future Work Record 2D-LIF spectra of fluorobenzene Possibility of time-resolved study Show usefulness of scheme when applied to other monosubstituted benzenes - coming up next!  Introduction - Existing schemes  M notation - Mass trends - G-W Notation  Experiments - Previous studies - Fluorobenzene - Fluorobenzene-d 5  Conclusions - Future Work

Acknowledgements Prof. Timothy G. Wright Anna Andrejeva William Tuttle Igor Pugliesi Christian Schriever