Academic Staff

Research Expertise

My research involves the use of both experimental and theoretical techniques for the elucidation of molecular structure and energetics of both stable and transient chemical systems. Present studies are concentrated on the adduct-anions of fullerenes, as revealed by electrospray mass spectrometry, and the cation states of binary complexes studied by ZEKE spectroscopy. Recent collaborations include studies of the UPS of reactive molecules, and a study of diatomic Rydberg states by REMPI-PES.

A. Structure and Bonding in Fullerene Compounds

The recent and continuing excitement in the world of Chemistry generated by the synthesis of C₆₀ and its related fullerenes has seen the development of an extensive synthetic and analytical programme on these and their compounds in many laboratories. The confident expectation is that a range of unique new materials will result from this research. However, the number of isolated and characterised molecular compounds of C₆₀ is still rather small, and at present is mainly of small adducts of simple functional groups. The present programme of fullerene studies has both experimental and theoretical aspects, including measurements by mass spectrometry, and calculations of molecular structures and energies.

(i) Electrospray Mass Spectrometry of Anionic Fullerene Species

The C₆₀ molecule is highly electrophilic and readily forms reduced species from C₆₀^- to C₆₀^6-. This suggests that the reactions of C₆₀ and other fullerenes should be suitably monitored and characterised using electrospray mass spectrometry operating in the negative-ion mode. We have recently observed some adduct-anions of C₆₀ by this technique, including species such as C₆₀(CN)^- and C₆₀(CN)₆^2-, as well as unusual complexes including the dimer [C₆₀(CN)₂^-]₂. Analogous cyano-adduct-anions are formed by C₇₀. Among the known higher fullerenes from C₇₆ to C₉₈, all can be identified in a mixture by reaction with CN^-, specifically through their C_n(CN)₂^2- species. Uniquely among fullerene anions, the dianions C₈₄^2- and C₉₀^2- have been shown as stable in the gas-phase.

(ii) Molecular Orbital Calculations of Fullerene Compounds

The MOPAC semiempirical program, which is designed for application to large molecules, is proving to be convenient for theoretical studies of the fullerenes and their adducts. Contrasting ab initio studies have commenced for some of the smaller adduct species such as the anions, C₆₀(CN)₂^2- and C₇₀(CN)₂^2-, as observed by electrospray mass spectrometry. Initial semiempirical calculations indicate that the optimum structures for these dianions are rather different, with C₆₀(CN)₂^2- preferring a structure with CN^- groups located on opposite sides of the C₆₀ sphere, but in C₇₀(CN)₂^2- the favored structure has the two CN^- adducts in near-proximity occupying adduct sites influenced by the unique 'equatorial' region of the oblate spheroid. The structure of the radical dimer species [C₆₀(CN)₂^-]₂ is also being investigated. The preferred isomers of the dianions C₈₄^2- and C₉₀^2- are also suggested by MOPAC AM1 calculations.

[1] "Cyano Adduct Anions of Higher Fullerenes: Electrospray Mass Spectrometric Studies",
G. Khairallah and J. B. Peel, Int. J. Mass. Spec., 194 (2000) 115-20.

B. Structure and Bonding in Binary Molecular Complexes

The neutral molecular complexes studied by Resonance-Enhanced Multiphoton Ionisation (REMPI) spectroscopy, and their cation analogues studied by Zero Electron Kinetic Energy (ZEKE) spectroscopy, offer interesting contrasts and challenges for structural studies by advanced methods including Density Functional Theory (DFT). The BLYP and B3LYP approximations have been compared with the established MP2 approach for the ZEKE-characterized binary complexes phenol.N₂ and phenol.CO [1]. Both methods give acceptable values of properties such as the intermolecular van der Waals vibration frequencies of the ground-state cation, in good agreement with the data obtained by ZEKE-PFI spectroscopy. ZEKE-PFI spectroscopy is most successful in cases where the neutral and cation species are each bound in their ground-states and exhibit similar geometries. Current research is aimed at finding candidate complexes for ZEKE studies based on this principle, with complexes of benzonitrile, C₆H₅CN, of present interest.

[1] "A Comparison of Hydrogen-bonded and van der Waals Isomers of Phenol..nitrogen and Phenol..carbon monoxide: an ab initio Study",
D.M. Chapman, K. Muller-Dethlefs and J.B. Peel, J. Chem. Phys., 111 (1999) 1955-63.

C. Collaborative Studies

1. Semiempirical and ab initio calculations on disaccharide species directed to understanding mass spectrometric observation (with J.C. Traeger, La Trobe University, Melbourne).
   [1] "Relative Gas-phase Acidities of Glucopyranose from Molecular Orbital Calculations",
   B. Mulroney, J.B. Peel and J.C. Traeger, J. Mass Spectrom., 34 (1999) 544-53.
   [2] "Theoretical Study of Deprotonated Glucopyranosyl Disaccharide Fragmentation",
   B. Mulroney , J.B. Peel and J.C. Traeger, J. Mass Spectrom., 34 (1999) 856-71.

2. Density functional calculations related to ZEKE observations (with K Muller-Dethlefs, University of York).
   [1] "Calculations on the Jahn-Teller Configurations of the Benzene Cation"
   K.Muller-Dethlefs and J.B. Peel, J. Chem. Phys., 111 (1999) 10550-4.

3. REMPI photoelectron spectroscopy of diatomic molecules (with C A de Lange, University of Amsterdam).
   [1] "Resonance-enhanced Multiphoton Ionisation Photoelectron Spectroscopy of the ClO Radical: the C²Sigma^- State",
   D.H.A.ter Steege, M. Smits, C.A. de Lange, N.P.C. Westwood, J.B. Peel and L. Visscher,
   Faraday Discuss., 115 (2000) 259-69.