Theoretical Studies of Negative Ions and their Corresponding Neutrals

               

Principal Investigator

John Bowie

Department of Chemistry

University of Adelaide

Co-Investigators

Stephen Blanksby

Suresh Dua

Sam Peppe

Department of Chemistry,

University of Adelaide

Leo Radom

Research School of Chemistry

Projects

g77-PC

Ab initio Molecular Orbital calculations carried out
on the PC provide us with complementary
information to that provided by our Negative Ion Mass Spectrometric experiments. Sophisticated algorithms allow us to obtain the accurate structures, energies and thermochemical properties of gas phase anions. Calculations allow us to understand and predict rearrangements of the anions and neutrals we observe experimentally. Exciting new experimental techniques allow us to explore the structures and chemistry of transient gas phase neutrals and we will expand our theoretical focus to encompass these new systems.
   
             

     
             

 

 

What are the results to date and the future of the work?

The Formation, Structures and Reactivity of Interstellar Molecules

Our main emphasis during the past year has been to prepare neutrals of interstellar significance in the mass spectrometer by charge stripping of anions of known connectivity and to characterise these molecules by their positive and negative ion mass spectra. In addition, structures and energies of all neutrals and anions have been determined using Gaussian 94 and Molpro 97.4. The following neutrals have been reported, viz three neutral isomers of C5H2, two isomers of neutral C5H, linear C7H2, and linear C5O and C7O. The syntheses of the precursors to linear C7H2 and to linear C5O (both interstellar molecules) are shown in eqns 1 and 2.

HO- + DCC-CC-CC-CH2OMe Æ -CC-CC-CC-CH2-OMe + HOD

Æ [C=C=C=C=C=C=CH2]-. + HOD + MeO. (1)

               
- Appendix B

 
               

       

F- + Me3Si-CC-CC-CO-tert C4H9 Æ -CC-CC-CO-tert C4H9 + Me3SiF Æ [C=C=C=C=C=O]-. + Me3SiF + tert C4H9. (2)

 

The continuation of this work into 1999 will include the preparation of isomers of C7H, C7H2, C5O and C7O. As an example, linear C5O is formed by charge stripping of the product formed in eqn 2. It is hoped that the reaction between Me3SiC2COC2SiMe 3 and SF6 (SF6 generates F- in the gas phase) will enable the formation of the symmetrical radical anion [C2COC2]-. which upon removal of an electron, will produce the required neutral C2COC2. Ab initio calculations will be used to determine the structures of all these isomers and to investigate whether particular isomers are interconvertible under interstellar conditions.

What computational techniques are used?

The program packages which have been used for the work described here are Gaussian 94 and Molpro, both of which are implemented on the PC.

Publications

S.J.Blanksby, S.Dua, J.H.Bowie, D.Schröder and H.Schwarz, Gas Phase Syntheses of Three Isomeric C5H2 Radical Anions and Conversion to their Elusive Neutrals, J.Phys.Chem. , 102, 9949-9956, 1998

S.Dua, S.J.Blanksby and J.H.Bowie, The Synthese of C6CH2-. and the Corresponding Carbenoid Cumulene C6CH2 in the Gas Phase Chem. Commun., 1767-1768 , 1998.

       

 

Appendix B -